Champak's Blog

The Eight Queens Problem : Explanation

2026-09-12T09:17:00.910+05:30

Eight Queens Problem Using Backtracking

The Eight Queens problem is a classic combinatorial problem. The objective is to place eight queens on an 8 × 8 chessboard so that no two queens can attack each other.

Therefore, no two queens may share:

The same row
The same column
The same diagonal

How backtracking solves the problem

Backtracking builds a solution one row at a time. A queen is placed in a safe column, and the algorithm then advances to the next row. If no safe position is available, it returns to the previous row and tries another position.

If two queens occupy positions (row1, column1) and (row2, column2), they attack each other when:

column1 === column2

Math.abs(row1 - row2) === Math.abs(column1 - column2)

Select “Generate Solutions” to begin.

JavaScript backtracking algorithm

function solveQueens(row) {
  if (row === 8) {
    solutions.push([...positions]);
    return;
  }

  for (let column = 0; column < 8; column++) {
    if (isSafe(row, column)) {
      positions[row] = column;
      solveQueens(row + 1);
    }
  }
}

The Eight Queens problem has 92 solutions. The interactive demonstration above lets you inspect them individually or play them automatically.

Learn With Champak: This is an excellent example for understanding recursion, constraint checking and backtracking.

Some sorting methods in C

2012-06-16T22:58:00.000+05:30

BubbleSort

#include<stdio.h>
int main()
{
int i,j,t,a[]={3,9,7,1,4},n=5;
for(i=0;i<=(n-2);i++)
for(j=0;j<5-i-1;j++)
{ if(a[j]>a[j+1])
{t=a[j];
a[j]=a[j+1];
a[j+1]=t;
}
}
for(i=0;i<5;i++)
printf("%d,",a[i]);
return(0);
}

CountingSort

#include<stdio.h>
int main()
{
int i,t,a[]={8,7,4,1,0,5,9,2},b[]={0,0,0,0,0,0,0,0,0,0},j,k=0;
for(i=0;i<8;i++)
printf("%d,",a[i]);
printf("\n\n");
for(i=0;i<8;i++)
{ t=a[i];
b[t]=b[t]+1;
}
for(i=0;i<10;i++)
printf("%d,",b[i]);
printf("\n\n");
for(i=0;i<10;i++)
{ if(b[i]==0)
continue;
t=b[i];
for(j=0;j<t;j++)
{a[k]=i;
k++;
}
}
for(i=0;i<8;i++)
printf("%d,",a[i]);
printf("\n\n");
/*Time complexity 3n*/
return(0);
}

HeapSort

#include<stdio.h>
int main()
{
int i,a[]={0,68,-7,45,6,57},n=6,t,k,l;
int b[n+1];
int left,right,pos,j,parent;

for(i=0;i<6;i++)
{
b[i+1]=a[i];
j=i+1;
while(1)
{
parent=j/2;
if(parent<1)
break;
if(b[parent]>=b[j])
break;
t=b[parent];
b[parent]=b[j];
b[j]=t;
j=parent;
}
}
for(i=1;i<7;i++)
printf("%d,",b[i]);
printf("\n\n");

for(i=1;i<=n;i++)
{
a[n-i]=b[1];
l=n-i+1;
b[1]=b[l];
l--;
j=1;
while(1)
{
left=2*j;
right=2*j+1;
if(left>l)
break;
if(right>l)
{
if(b[j]>b[left])
break;
t=b[j];
b[j]=b[left];
b[left]=t;
break;
}
if(b[left]>b[right])
pos=left;
else
pos=right;
if(b[j]>b[pos])
break;
t=b[pos];
b[pos]=b[j];
b[j]=t;
j=pos;
}
}

for(i=0;i<6;i++)
printf("%d,",a[i]);
printf("\n\n");

/*Time complexity nlog(base 2)n*/
/*For Quick and Merge too.*/
return(0);
}

InsertionSort

#include<stdio.h>
int main()
{

int i,j,t,a[]={5,9,3,0,1},n=5;
for(i=0;i<=n-2;i++)
{
if(a[i]<=a[i+1])
continue;

j=i+1;
t=a[j];
while(j>=1 && a[j-1]>t)
{ a[j]=a[j-1];
j--;
}
a[j]=t;
}
for(i=0;i<n;i++)
printf("%d,",a[i]);
return(0);
}

MergeSort

#include<stdio.h>

void mergesort(int a[],int left,int right);
void main()
{
int i;
int a[]={9,6,8,2,5,90,-8,4,1,10};
mergesort(a,0,9);
for(i=0;i<10;i++)
printf("%d,",a[i]);
printf("\n\n");
}
void mergesort(int a[],int left,int right)
{
int c[10];
int p,mid,i,j,k;
if(left>=right)
return;
mid=(left+right)/2;
mergesort(a,left,mid);
mergesort(a,mid+1,right);
i=left;
j=mid+1;
k=0;
while(i<=mid && j<=right)
{
if(a[i]<=a[j])
{
c[k]=a[i];
i++;
}
else
{
c[k]=a[j];
j++;
}
k++;
}
if(i<=mid)
for(p=i;p<=mid;p++)
{
c[k]=a[p];
k++;
}
else
for(p=j;p<=right;p++)
{
c[k]=a[p];
k++;
}

for(i=left;i<=right;i++)
a[i]=c[i-left];

printf("\nleft=%d right=%d\n",left,right);

for(i=0;i<10;i++)
printf("%d,",a[i]);
printf("\n\n");
}

QuickSort

#include<stdio.h>
void quicksort(int a[],int left,int right);
int main()
{
int i,fp,pivot,t,a[]={9,1,17,3,10,-8,5},n=7;
quicksort(a,0,n-1);
for(i=0;i<n;i++)
printf("%d,",a[i]);
return(0);
}
void quicksort(int a[],int left,int right)
{
int i,fp,pivot,t;
if(left>=right)
return;
fp=left;
pivot=a[left];

for(i=left + 1;i<=right;i++)
{
if(a[i]>=pivot)
continue;

fp++;
t=a[i];
a[i]=a[fp];
a[fp]=t;

}
t=a[fp];
a[fp]=pivot;
a[left]=t;
quicksort(a,left,fp-1);
quicksort(a,fp+1,right);
}

SelecionSort

#include<stdio.h>
int main()
{
int i,j,smallpos,a[]={3,9,7,1,4},t;
for(i=0;i<1;i++)
{
smallpos=i;
for(j=i+1;j<=4;j++)
if(a[j]<a[smallpos])

smallpos=j;
t=a[smallpos];
a[smallpos]=a[i];
a[i]=t;
a[0]=a[i];

}
printf("%d",a[0]);
return(0);
}

Detecting mouse positions through JavaScript

2012-06-16T22:22:00.000+05:30

Methods of Console IO in Java

2012-06-09T10:58:00.001+05:30

In this Post we shall study the methods of Console IO in Java. We shall examine 4 different methods for doing so.However, first of all we require some background information:-

The Standard Input, Standard Output & Standard Error

As , we all know every process is given three open streams by the operating system. Namely , Standard Input,Standard Output and Standard Error.

Standard Input:- The standard input is known as stdin in C, cin in C++ and System.in in Java. By default it is the keyboard but it can be reassigned. System.in is an object of type java.io.InputStream and provides a method read(), which reads the next int from the input source. It returns -1 on End Of File (EOF). From the keyboard we can simulate EOF by pressing CTRL + Z .This will show ^Z on the screen.

Standard Output:- The standard output is known as stdout in C,cout in C++ and System.out in Java. By default it is the monitor but it can be redirected. It is represented in Java by an object of type java.io.PrintStream.

Standard Error:- The standard error is known as stderr in C,cerr in C++ and System.err in Java. By default it is the monitor but it can be redirected. It is represented in Java by an object of type java.io.PrintStream.

Reading Input Directly from the Standard Input using System.in

DirectIO.java

public class DirectIO
{

public static void main(String[] args)
{
//Enter the testing code here
}
public static int readInt()
{
return Integer.parseInt(readLine());
}

public static String readString()
{
try
{
String s="";
while(true)
{
int n=System.in.read();
if(n==-1 || n==13 || n==' ')
return s.trim();
char ch=(char)n;
s=s+ch;
}
}
catch(Exception ex)
{
return "";
}
}

public static String readLine()
{
try
{
String s="";
while(true)
{
int n=System.in.read();
if(n==-1 || n==13)
return s.trim();
char ch=(char)n;
s=s+ch;
}
}
catch(Exception ex)
{
return "";
}
}
}

Explanation: In the the readLine and readString methods we simply read the next input from System.in. This is an int and is stored in n. If n is 13 we have <Enter> being pressed , while n==-1 means an EOF. In both cases we return the current Line. Till these conditions are met , we simply append the next character to the input.
For readString, we also check for the space character ' '.

For readInt, we simply convert the already read Line or String to the required type.

For reading and printing a line use:-

String str=readLine();

System.out.println(str);
For reading and printing an int use:-

int str=readInt();

System.out.println(str);

For reading and printing a Stringuse:-

String str=readString();

System.out.println(str);

For reading and printing a list of Strings :-

String str=readString();
while(str!="")
{
System.out.println(str);
str=readString();
}

Using the java.util.Scanner class
The Scanner class in java.util is a very versatile instrument for text input. It can read all types of data , and from a variety of data sources.The Scanner essentially has two groups of methods:-

1) The hasNextType group. This group returns true if some input of the given type is available and returns false otherwise.
Some functions are hasNext for Objects, hasNextLine for Lines,hasNextInt for integers, and so on.

2) The hasType group. This group returns the next type element from the input source.Some examples are:-
next reads Object, nextLine reads Line, nextInt reads Integers and so on.

Here is some sample code:-

import java.util.Scanner;
public class ScannerIO
{
public static void main( String[] args)
{
Scanner s=new Scanner(System.in);
int a =s.nextInt();
System.out.println(a);
}
}

To be continued...

Drawing Pyramids

2012-06-02T17:07:00.041+05:30

#include<stdio.h>

#include<conio.h>

void main()

{

int n=5,i,j,k;

clrscr();

for(i=1;i<=n;i++)

{

for(j=1;j<=n-1;j++)

printf(" ");

for(k=1;k<=i;k++)

printf("*");

printf("\n");

}

getch();

}

#include<stdio.h>
#include<conio.h>
void main()
{
int n=5,i,j,k;
clrscr();
for(i=1;i<=n;i++)
{
for(j=1;j<=0;j++)
printf(" ");
for(k=1;k<=i;k++)
printf("*");
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
void main()
{
int n=5,i,j,k;
clrscr();
for(i=1;i<=n;i++)
{
for(j=1;j<=n-i;j++)
printf(" ");
for(k=1;k<=2*i-1;k++)
printf("*");
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int n=5,i,j,k;
int x,y;
clrscr();
for(i=1;i<=n;i++)
{
for(j=1;j<=n-i;j++)
printf(" ");
for(k=1;k<=2*i-1;k++)
{
x=i-abs(i-k);
printf("%d",x);
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int n=5,i,j,k;
int x,y;
clrscr();
for(i=n;i>=1;i--)
{
for(j=1;j<=n-i;j++)
printf(" ");
for(k=1;k<=2*i-1;k++)
{
x=i-abs(i-k);
printf("%c",'A' + x -1);
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int n=5,i,j,k;
clrscr();
for(i=1;i<=n;i++)
{
for(j=1;j<=n-i;j++)
printf(" ");
for(k=1;k<=i;k++)
{
printf("* ");
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
int pascalvalue(int y,int x);
void main()
{
int n=5,i,j,k;
clrscr();
for(i=1;i<=n;i++)
{
for(j=1;j<=n-i;j++)
printf(" ");
for(k=1;k<=i;k++)
{
printf("%d ",pascalvalue(i,k));
}
printf("\n");
}
getch();
}

int pascalvalue(int y,int x)
{
if(x==1)
return(1);
if(x==y)
return(1);
return(pascalvalue(y-1,x-1) + pascalvalue(y-1,x));
}

#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
int n=5,i,j,k;
int mid=(n+1)/2,x,y;
clrscr();
for(i=1;i<=n;i++)
{
x=abs(mid-i);
y=mid-x;
for(j=1;j<=y;j++)
printf(" ");
for(k=1;k<=2*x+1;k++)
printf("*");
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
int n=5,i,j,k;
int mid=(n+1)/2,x,y,z;
clrscr();
for(i=1;i<=n;i++)
{
x=abs(mid-i);
y=mid-x;
for(j=1;j<=y;j++)
printf(" ");
for(k=1;k<=2*x+1;k++)
{
z=x-abs(x+1-k)+1;
printf("%d",z);
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
int n=5,i,j,k;
int mid=(n+1)/2,x,y,l,r;
clrscr();
for(i=1;i<=n;i++)
{
x=abs(mid-i)+1;
y=mid-x;
for(j=1;j<=n;j++)
{
l=j;
r=n+1-j;
if(j<=x || r<=x)
printf("*");
else
printf(" ");
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
int n=11,i,j,k;
int mid=(n+1)/2,x,y,l,r,z;
clrscr();
for(i=1;i<=n;i++)
{
x=abs(mid-i)+1;
y=mid-x;
for(j=1;j<=n;j++)
{
l=j;
r=n+1-j;
z=abs(mid-j);
if(j<=x || r<=x)
printf("%d",z);
else
printf(" ");
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
int n=11,i,j,k;
int mid=(n+1)/2,x,y,l,r,z;
clrscr();
for(i=1;i<=n;i++)
{
x=abs(mid-i)+1;
y=mid-x;
for(j=1;j<=n;j++)
{
l=j;
r=n+1-j;
z=mid-abs(mid-j)-1;
if(j<=x || r<=x)
printf("%c",'A' + z);
else
printf(" ");
}
printf("\n");
}
getch();
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
#define n 4
void main()
{

int l=0,r=n-1,t=0,b=n-1,i,x=1,j;
int a[n][n];
clrscr();
while(x<=n*n)
{
for(i=l;i<=r;i++)
a[t][i]=x++;
t++;
for(i=t;i<=b;i++)
a[i][r]=x++;
r--;
for(i=r;i>=l;i--)
a[b][i]=x++;
b--;
for(i=b;i>=t;i--)
a[i][l]=x++;
l++;
}
for(i=0;i<=n-1;i++)
{
for(j=0;j<=n-1;j++)
printf("%4d",a[i][j]);
printf("\n");
}
getch();
}

Pointers in C

2012-05-28T15:43:00.000+05:30

A pointer is the address of a variable.For understanding pointers let us consider the following declarations:-

There are only two operators in C regarding pointers.
& is the addressing operator, and when applied to a variable gives it's address.

* is the value or indirection operator. When applied to an address it gives the value at the address.

1)
int x=10;
int *p=&x;
int **q=&p;

x is a variable of type int. It's value is 10. Let us assume it's address is 1000.

int *p; *p is an int, p is the address of an int.The value of p is &x i,e address of x which is 1000.

int **q; **q is an int, *q is a pointer to int, q is a pointer to pointer to int.

x is thus equivalent to *p and both are 10.
&x is equivalent to p and is 1000

What is &*p?
replace *p by x, we get &x which is p .
Therefore we can say that &* cancel out.

The same is true for *&x.

Consider this program :-
*******************************ptr.c**************************
#include<stdio.h>
#include<conio.h>
void main()
{
int x=10;
int *p=&x;
clrscr();
printf("%u,%d\n",&x,x);
printf("%u,%d\n",p,*p);
getch();
}

The output:-

64948,10
64948,10

The equivalence of Arrays & Pointers.

The following program should be self explanatory:-

#include<stdio.h>
#include<conio.h>
void main()
{
int a[]={1,2,3,4,5},n=5,i;
int *p=a;
clrscr();
for(i=0;i<=n-1;i++)
printf("%d,",*(p+i));
printf("\n");
for(p=a;p<=&a[n-1];p++)
printf("%d,",*p);
printf("\n");
for(p=a;p<=&a[n-1];)
printf("%d,",*p++);
printf("\n");
//This reads the array using array syntax
for(i=0;i<=n-1;i++)
scanf("%d",&a[i]);
for(p=a;p<=&a[n-1];)
printf("%d,",*p++);
printf("\n");
//Since &a[i] translates to p+i, therefore we have
for(p=a;p<=&a[n-1];)
scanf("%d",p++);
printf("\n");

for(p=a;p<=&a[n-1];)
printf("%d,",*p++);
printf("\n");
getch();
}
The output:-

Parameter passing using pointers

#include<stdio.h>
#include<conio.h>
void valueswap (int a,int b);
void ptrswap(int* a,int* b);
void main()
{
int x=5,y=10;
clrscr();
printf("Value before value swap a = %d, b = %d\n",x,y);
valueswap(x,y);
printf("Value after value swap a = %d, b = %d\n",x,y);
printf("Value before ptr swap a = %d, b = %d\n",x,y);
ptrswap(&x,&y);
printf("Value after ptr swap a = %d, b = %d\n",x,y);
getch();
}
void valueswap (int a,int b)
{
int t=a;
a=b;
b=t;
}
void ptrswap(int* a,int* b)
{
int t=*a;
*a=*b;
*b=t;
}

The output:-

To understand this assume the following.

Variable    |    Value    |    Address
x                    5               1000
y                    10             1002

for valueswap

void valueswap (int a,int b)
{
int t=a;
a=b;
b=t;
}

after parameter copy
a=5
b=10

int t=a; t = 5
a=b; a=10;
b=t; b=5

The values of x and y are not changed. Therefore the output in main remains unaffected .

For ptrswap

void ptrswap(int* a,int* b)
{
int t=*a;
*a=*b;
*b=t;
}

It is called as ptrswap(&x,&y);=ptrswap(1000,1002);
Therefore after parameter passing a=1000, and b=1002

int t=*a which translates as t=*1000 which means value at address 1000 which is the value of x ans is 5.
so t=5;

*a=*b, which translates as *1000 = * 1002. Replace value at address 1000 with value at address 1002.
This means that x becomes 10.

*b=t; which translates as *1002=5. Therefore value at address 1002, i,e y becomes 5.

Therefore , x and y are swapped.

Implementing 1's Complement & 2's Complement in C

2012-05-19T18:12:00.000+05:30

1's complement and 2's complement arithmetic is used in Computer Science for implementing the basic operations of addition and subtraction. In this program , I have endeavored to provide a simple menu based example in C of these basic operations.

To implement these operations I have developed the following functions:-

void printMenu()
{
clrscr();
gotoxy(5,5);
printf("Read\tPrint\t1'sComplement\t2'sComplement\tAdd\tSub\teXit\n");
printf("A = ");
printNumber(a);
printf(" B = ");
printNumber(b);
printf(" C = ");
printNumber(c);
printf("\n");
}This is the Menu. It works by pressing R,P,1,2,A,S,X

The menu is not case sensitive.

void copyArray(int dest[],int src[])
{
int i;
for(i=0;i<=8;i++)
dest[i]=src[i];
}

copies the src array into dest.

int getCarry(int a,int b,int c)
{
int sum=a+b+c;
switch(sum)
{
case 0:return(0);
case 1:return(0);
case 2:return (1);
default:return(1);
}
}adds 3 bits and returns the carry.

int getSum(int a,int b,int c)
{
int sum=a+b+c;
switch(sum)
{
case 0:return(0);
case 1:return(1);
case 2:return (0);
default:return(1);
}
}

Adds three bits and returns the sum

void TwosComplement(int x[])
{
int temp[]={1,0,0,0,0,0,0,0,0};
int out[9];
copyArray(out,x);
OnesComplement(out);
addNumber(out,temp,x);
}

finds the 2's complement of a number and stores it in the same array.

void OnesComplement(int x[])
{
int i;
for(i=8;i>=0;i--)
x[i]=1-x[i];
}

finds the 1's complement of a number.

void printNumber(int x[])
{
int i;
for(i=8;i>=0;i--)
printf("%d",x[i]);
}

prints the number

void readNumber(int x[])
{
int i;
char str[10];
scanf("%s",str);
for(i=8;i>=0;i--)
x[i]=(str[8-i]-'0'); //0,1,2,3,4 '0'-'0'=0,'1'-'0'=1
}

reads a number as a string of 9 characters and stores it in a int array.

void subNumber(int x[],int y[],int sub[])
{
int temp[9];
copyArray(temp,y);
TwosComplement(temp);
addNumber(x,temp,sub);
}

subtracts 2 numbers and stores it in the 3rd parameter

Important

Each array is 9 elements, 8 for the byte and the ninth for the sine bit.

Therefore values must be entered as such

Here are some snapshots:-

The Complete Program

Binary.c

#include<stdio.h>
#include<conio.h>
#include<math.h>
int a[9]={0,0,0,0,0,0,0,0,0},b[9]={0,0,0,0,0,0,0,0,0},c[9]={0,0,0,0,0,0,0,0,0};
void readNumber(int x[]);
void printNumber(int x[]);
void OnesComplement(int x[]);
void addNumber(int x[],int y[],int sum[]);
void TwosComplement(int x[]);
int getSum(int a,int b,int c);
int getCarry(int a,int b,int c);
void copyArray(int dest[],int src[]);
void subNumber(int x[],int y[],int sub[]);
void printMenu();
void main()
{

int option,ch;
clrscr();
while(1)
{
printMenu();
option=getch();
switch(option)
{
case'X':
case'x':
return;
case 'r':
case 'R':
printf("\nEnter a or b: ");
ch=getche();
printf(" = ");
if(ch=='a' || ch=='A')
readNumber(a);
else
readNumber(b);
break;
case '1':
printf("\nEnter a or b: ");
ch=getche();
printf(" = )");
if(ch=='a' || ch=='A')
OnesComplement(a);
else
OnesComplement(b);
break;

case '2':
printf("\nEnter a or b: ");
ch=getche();
printf(" = ");
if(ch=='a' || ch=='A')
TwosComplement(a);
else
TwosComplement(b);
break;
case 'a':
case 'A':
addNumber(a,b,c);
break;
case 's':
case 'S':
subNumber(a,b,c);
break;
}
}
}
void printMenu()
{
clrscr();
gotoxy(5,5);
printf("Read\tPrint\t1'sComplement\t2'sComplement\tAdd\tSub\teXit\n");
printf("A = ");
printNumber(a);
printf(" B = ");
printNumber(b);
printf(" C = ");
printNumber(c);
printf("\n");
}
void copyArray(int dest[],int src[])
{
int i;
for(i=0;i<=8;i++)
dest[i]=src[i];
}
void addNumber(int x[],int y[],int sum[])
{
int i,s,carry=0;
for(i=0;i<=8;i++)
{
   s=getSum(x[i] ,y[i],carry);
   carry=getCarry(x[i],y[i],carry);
   sum[i]=s;
}
}
int getCarry(int a,int b,int c)
{
int sum=a+b+c;
switch(sum)
{
case 0:return(0);
case 1:return(0);
case 2:return (1);
default:return(1);
}
}
int getSum(int a,int b,int c)
{
int sum=a+b+c;
switch(sum)
{
case 0:return(0);
case 1:return(1);
case 2:return (0);
default:return(1);
}
}
void TwosComplement(int x[])
{
int temp[]={1,0,0,0,0,0,0,0,0};
int out[9];
copyArray(out,x);
OnesComplement(out);
addNumber(out,temp,x);
}
void OnesComplement(int x[])
{
int i;
for(i=8;i>=0;i--)
x[i]=1-x[i];
}
void printNumber(int x[])
{
int i;
for(i=8;i>=0;i--)
printf("%d",x[i]);
}

void readNumber(int x[])
{
int i;
char str[10];
scanf("%s",str);
for(i=8;i>=0;i--)
x[i]=(str[8-i]-'0'); //0,1,2,3,4 '0'-'0'=0,'1'-'0'=1
}
void subNumber(int x[],int y[],int sub[])
{
int temp[9];
copyArray(temp,y);
TwosComplement(temp);
addNumber(x,temp,sub);
}

Next, we shall use it to implement the Booth's algorithm

Joins in MS SQL Server,Oracle & MY SQL

2012-05-10T23:01:00.001+05:30

Joins are a way of connecting data from more than one table.We can also have joins on the same table by creating aliases. There are four basic joins
1) Outer join
2) Left outer join
3) Right outer join
4) inner join.

In this post, we shall learn the syntax of joins on MS SQL Server, Oracle & MY SQL.

First, the tables:-

1) create table medicalcharlatans(CharlatanName varchar(100) primary key,CharlatanRank int,CharlatanDescrption varchar(200))

Then insert some data.

insert into medicalcharlatans values('Jesus Christ',1,'Used to treat diseases by driving out demons')
insert into medicalcharlatans values('Mother Teresa',2,'Cured cancer via Light Emitting Photo')
insert into medicalcharlatans values('Benny Hinn',3,'Cured diseases via Touch Therapy')

Here is a view of the table:-
Benny Hinn    3    Cured diseases via Touch Therapy
Jesus Christ    1    Used to treat diseases by driving out demons
Mother Teresa    2    Cured cancer via Light Emitting Photo

2) create table PedofileProtectors(ProtectorName varchar(100) primary key,ProtectorDescrption varchar(200))

insert into PedofileProtectors values('John Paul 2','Protected Pedofiles and promoted Pedofile protectors like Mother Teresa and Ratzinger')

insert into PedofileProtectors values('Ratzinger','Protected Pedofiles and promoted Pedofile protectors like Mother Teresa and John Paul 2')

insert into PedofileProtectors values('Mother Teresa','Protected Pedofiles and promoted Pedofile protectors like John Paul 2 and Ratzinger, wrote letters of support for recognized Pedofiles')

The table as it stands now :-

John Paul 2    Protected Pedofiles and promoted Pedofile protectors like Mother Teresa and Ratzinger

Mother Teresa    Protected Pedofiles and promoted Pedofile protectors like John Paul 2 and Ratzinger, wrote letters of support for recognized Pedofiles

Ratzinger    Protected Pedofiles and promoted Pedofile protectors like Mother Teresa and John Paul 2

The various Joins :-

Cross Join

The cross join is a cartesian product. Here is the output in MS SQL Server. Incidentally , it's the same in all three databases.

select * from medicalcharlatans cross join PedofileProtectors
This is supported by all three databases

SELECT CharlatanName,ProtectorName FROM medicalcharlatans full outer JOIN PedofileProtectors ON CharlatanName = ProtectorName
Not supported in my SQL. We shall learn in a subsequent post to simulate it using Union.

SELECT CharlatanName,ProtectorName FROM medicalcharlatans right outer JOIN PedofileProtectors ON CharlatanName = ProtectorName
It's supported in Oracle.
In My SQL :- SELECT CharlatanName,ProtectorName FROM medicalcharlatans right JOIN PedofileProtectors ON CharlatanName = ProtectorName

SELECT CharlatanName,ProtectorName FROM medicalcharlatans left outer JOIN PedofileProtectors ON CharlatanName = ProtectorName

It's supported in Oracle.
In My SQL :- SELECT CharlatanName,ProtectorName FROM medicalcharlatans left JOIN PedofileProtectors ON CharlatanName = ProtectorName

SELECT CharlatanName,ProtectorName FROM medicalcharlatans inner JOIN PedofileProtectors ON CharlatanName = ProtectorName
SELECT CharlatanName,ProtectorName FROM medicalcharlatans JOIN PedofileProtectors ON CharlatanName = ProtectorName
It's supported in all three databases.

In a subsequent post, we shall discuss unions, intersections, minus, and the top and rownum

Session Listeners in Apache Tomcat

2012-04-12T14:29:00.000+05:30

To implement a SessionListener in java we implement the javax.servlet.http.HttpSessionListener interface.

Here is our implementation of the HttpSessionListener

CountSessionListener

package servletpackage;
import java.sql.*;
import javax.naming.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class CountSessionListener implements HttpSessionListener
{
public void sessionCreated(HttpSessionEvent event)
{
HttpSession session=event.getSession();
try
{

String id=session.getId();
java.util.Date d=new java.util.Date();
System.out.println("Session Created with ID=" + id + " at time " + d);
}
catch(Exception ex)
{
System.out.println(ex);
}
}
public void sessionDestroyed(HttpSessionEvent event)
{
HttpSession session=event.getSession();
try
{
String id=session.getId();
java.util.Date d=new java.util.Date();
System.out.println("Session Destroyed with ID=" + id + " at time " + d);
}
catch(Exception ex)
{
System.out.println(ex);
}
}
}

To redirect the Standard Output in Apache Tomcat we use the logging tab in the Tomcat Monitor.

To install this session listener the following entries are required in the web.xml file.

web.xml

<web-app>
<listener>
<listener-class>servletpackage.CountSessionListener</listener-class>
</listener>
<session-config>
<session-timeout>2</session-timeout>
</session-config>
</web-app>

The underlined portion is the session listener configuration. We have also set a session timeout of 2 minutes.

To test the listener create two jsp pages. hello.jsp, and bye.jsp. hello.jsp creates a session while bye.jsp destroys it.

Here are the two files:-

hello.jsp

<%
request.getSession(true);
%>

bye.jsp

<%
session.invalidate();
%>

Open the two files and refresh them alternately in the browser.

Here is the output in the out.txt file where the System.out is redirected.

2012-04-12 14:01:32 Commons Daemon procrun stdout initialized
Session Created with ID=EA0AEFF5335E7F8E9B59F99FBDA5157D at time Thu Apr 12 14:01:44 IST 2012
Session Destroyed with ID=EA0AEFF5335E7F8E9B59F99FBDA5157D at time Thu Apr 12 14:02:05 IST 2012
Session Created with ID=2BE4BD1A6EFAA45785F63EB5991B46D1 at time Thu Apr 12 14:24:04 IST 2012
Session Destroyed with ID=2BE4BD1A6EFAA45785F63EB5991B46D1 at time Thu Apr 12 14:24:04 IST 2012
Session Created with ID=2BFF301ED2C87299CB0E75F51323340D at time Thu Apr 12 14:24:06 IST 2012

Exchanging the value of Variables

2012-04-12T12:15:00.001+05:30

In this post we shall look at the various ways of interchanging the values of variables. We shall not be looking into methods involving loops, but only simple expression based methods.

Essentially, any binary operation which has an inverse can be used as a basis for the exchange. Thus, we shall use the assignment operator, addition, subtraction, multiplication and division. The last two will require the divisor to be non zero.

Here is the program which does this exchange.

Exchange.c

#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
float a=15,b=10,t;
clrscr();
printf("Original values a=%f,b=%f",a,b);
printf("\nSwap using a temporary variable\n");
t=a;a=b;b=t;
printf("Swapped values a=%f,b=%f",a,b);
printf("\nSwap using a substraction\n");
a=a-b;b=a+b;a=b-a;
printf("Swapped values a=%f,b=%f",a,b);
printf("\nSwap using a addition\n");
a=a+b;b=a-b;a=a-b;
printf("Swapped values a=%f,b=%f",a,b);
printf("\nSwap using a multiplication\n");
a=a*b;b=a/b;a=a/b;
printf("Swapped values a=%f,b=%f",a,b);
printf("\nSwap using a division\n");
a=a/b;b=a*b;a=b/a;
printf("Swapped values a=%f,b=%f",a,b);
getch();
}
This is the output of the program

Original values a=15.000000,b=10.000000
Swap using a temporary variable
Swapped values a=10.000000,b=15.000000
Swap using a substraction
Swapped values a=15.000000,b=10.000000
Swap using a addition
Swapped values a=10.000000,b=15.000000
Swap using a multiplication
Swapped values a=15.000000,b=10.000000
Swap using a division
Swapped values a=10.000000,b=15.000000

Rotation of values

Rotation of values a<--b, b<-- c, c<-- a

This is accomplished through the following program code.

#include<stdio.h>
#include<conio.h>
void main()
{
int a=1,b=2,c=3,t;
clrscr();
printf("Original values a=%d,b=%d,c=%d\n",a,b,c);
t=a;
a=b;
b=c;
c=t;
printf("Rotated values a=%d,b=%d,c=%d\n",a,b,c);
getch();
}

Here is the output of this program

Original values a=1,b=2,c=3
Rotated values a=2,b=3,c=1

Exchanging two elements via a temporary variable is a special case of the general rotation problem. As an interesting aside we can see that for n elements to be rotated, n rotations would give back the original set.

Database & DDL Triggers in Oracle

2012-02-19T20:35:00.000+05:30

In this post, we shall create a series of triggers to illustrate the use of Database triggers in Oracle.

Database Triggers:-

Database triggers are fired on Login & Logout. Let us create a trigger to maintain a list of logins & logouts. First a table to store the login information:-

create table LoginStats(username varchar(50),datetimeoflogin date)

Here is the trigger:-

create or replace trigger logintrigger
after logon on database
begin
insert into LoginStats values(ora_login_user,sysdate);
end;

A logon trigger can only be a after trigger.

A trigger for Logout

The table :

create table LogoutStats(username varchar(50),datetimeoflogout date)

create or replace trigger logofftrigger
before logoff on database
begin
insert into LogoutStats values(ora_login_user,sysdate);
end;

DDL Triggers are created for Create,Alter & Drop statements.

Here is a trigger that tracks created objects:-

create table CreatedObjects(CreatedByUser varchar(100),ObjectName varchar(100),ObjectType varchar(100),DateofCreation date)

CREATE or replace TRIGGER Databasecreateobjecttrigger AFTER CREATE
ON database
begin
insert into CreatedObjects values(ora_login_user,ora_dict_obj_name,ora_dict_obj_type,sysdate);
end;

For DML Triggers , please refer http://champakonline.blogspot.com/2010/10/some-triggers-in-oracle.html

Calling a Web Service through Android and passing Parameters

2012-02-17T22:33:00.000+05:30

In the last post http://champakonline.blogspot.com/2012/02/calling-web-service-through-android.html , we learned how to call a .Net Web Service from Android. In this post, we shall call a Web Service that requires parameters to be sent.
For this application, we shall use the Web Service whose WSDL is at http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx?WSDL

The WSDL is

<wsdl:definitions targetNamespace="http://tempuri.org/"><wsdl:types><s:schema elementFormDefault="qualified" targetNamespace="http://tempuri.org/"><s:element name="getBirthday"><s:complexType><s:sequence><s:element minOccurs="0" maxOccurs="1" name="name" type="s:string"/></s:sequence></s:complexType></s:element><s:element name="getBirthdayResponse"><s:complexType><s:sequence><s:element minOccurs="0" maxOccurs="1" name="getBirthdayResult" type="s:string"/></s:sequence></s:complexType></s:element><s:element name="GetAQuote"><s:complexType/></s:element><s:element name="GetAQuoteResponse"><s:complexType><s:sequence><s:element minOccurs="0" maxOccurs="1" name="GetAQuoteResult" type="s:string"/></s:sequence></s:complexType></s:element></s:schema></wsdl:types><wsdl:message name="getBirthdaySoapIn"><wsdl:part name="parameters" element="tns:getBirthday"/></wsdl:message><wsdl:message name="getBirthdaySoapOut"><wsdl:part name="parameters" element="tns:getBirthdayResponse"/></wsdl:message><wsdl:message name="GetAQuoteSoapIn"><wsdl:part name="parameters" element="tns:GetAQuote"/></wsdl:message><wsdl:message name="GetAQuoteSoapOut"><wsdl:part name="parameters" element="tns:GetAQuoteResponse"/></wsdl:message><wsdl:portType name="HypatiaQuotesServiceSoap"><wsdl:operation name="getBirthday"><wsdl:input message="tns:getBirthdaySoapIn"/><wsdl:output message="tns:getBirthdaySoapOut"/></wsdl:operation><wsdl:operation name="GetAQuote"><wsdl:input message="tns:GetAQuoteSoapIn"/><wsdl:output message="tns:GetAQuoteSoapOut"/></wsdl:operation></wsdl:portType><wsdl:binding name="HypatiaQuotesServiceSoap" type="tns:HypatiaQuotesServiceSoap"><soap:binding transport="http://schemas.xmlsoap.org/soap/http"/><wsdl:operation name="getBirthday"><soap:operation soapAction="http://tempuri.org/getBirthday" style="document"/><wsdl:input><soap:body use="literal"/></wsdl:input><wsdl:output><soap:body use="literal"/></wsdl:output></wsdl:operation><wsdl:operation name="GetAQuote"><soap:operation soapAction="http://tempuri.org/GetAQuote" style="document"/><wsdl:input><soap:body use="literal"/></wsdl:input><wsdl:output><soap:body use="literal"/></wsdl:output></wsdl:operation></wsdl:binding><wsdl:binding name="HypatiaQuotesServiceSoap12" type="tns:HypatiaQuotesServiceSoap"><soap12:binding transport="http://schemas.xmlsoap.org/soap/http"/><wsdl:operation name="getBirthday"><soap12:operation soapAction="http://tempuri.org/getBirthday" style="document"/><wsdl:input><soap12:body use="literal"/></wsdl:input><wsdl:output><soap12:body use="literal"/></wsdl:output></wsdl:operation><wsdl:operation name="GetAQuote"><soap12:operation soapAction="http://tempuri.org/GetAQuote" style="document"/><wsdl:input><soap12:body use="literal"/></wsdl:input><wsdl:output><soap12:body use="literal"/></wsdl:output></wsdl:operation></wsdl:binding><wsdl:service name="HypatiaQuotesService"><wsdl:port name="HypatiaQuotesServiceSoap" binding="tns:HypatiaQuotesServiceSoap"><soap:address location="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx"/></wsdl:port><wsdl:port name="HypatiaQuotesServiceSoap12" binding="tns:HypatiaQuotesServiceSoap12"><soap12:address location="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx"/></wsdl:port></wsdl:service></wsdl:definitions>

Since we shall be calling the getBirthday method. The relevant portions to remember are :-

1) <wsdl:definitions targetNamespace="http://tempuri.org/">

2) <soap:operation soapAction="http://tempuri.org/getBirthday" style="document"/>

3) <s:sequence><s:element minOccurs="0" maxOccurs="1" name="name" type="s:string"/></s:sequence>

The first one gives the namespace to be used, the second is the soap action, and the third is the parameter to be passed. The name of the parameter is "name" while the type is "s:string".

It is important to note that, should any of these three items be used wrongly, the parameter passing and calling would not work.

Here is the code for the activity:-

HypatiaFriendsActivity.java

package hypatia.friends;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import org.ksoap2.SoapEnvelope;
import org.ksoap2.serialization.PropertyInfo;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.HttpTransportSE;
public class HypatiaFriendsActivity extends Activity implements OnClickListener{
    /** Called when the activity is first created. */
    private Button b;
    private TextView tv;
    private EditText txtname;
    private TextView txtBirthday;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        b=(Button)findViewById(R.id.button1);
        tv=(TextView)findViewById(R.id.txtName);
        txtBirthday=(TextView)findViewById(R.id.txtBirthday);
        txtname=(EditText)findViewById(R.id.txtName);
        b.setOnClickListener(this);

    }
    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        try
        {
        String namespace = "http://tempuri.org/";
        String url ="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx?WSDL";
        String soapaction = "http://tempuri.org/getBirthday";
        String methodname = "getBirthday";
        SoapObject request = new SoapObject(namespace, methodname);
        request.addProperty("name","" + txtname.getText());
        SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
        envelope.dotNet=true;
        envelope.setOutputSoapObject(request);
        HttpTransportSE androidHttpTransport = new HttpTransportSE (url);


            androidHttpTransport.call(soapaction, envelope);
            org.ksoap2.serialization.SoapObject resultsRequestSOAP =(org.ksoap2.serialization.SoapObject) envelope.bodyIn;
            txtBirthday.setText("" + resultsRequestSOAP.getProperty(0));
        }
        catch(Exception ex)
        {
            tv.setText("" + ex);
        }
    }
}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

    <TextView
        android:id="@+id/txtBirthday"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/blank"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <EditText
        android:id="@+id/txtName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPersonName" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/buttontext" />

</LinearLayout>

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="hello">Hypatia Friend Finder</string>
    <string name="app_name">HypatiaFriends</string>
    <string name="buttontext">Get Birthday</string>
    <string name="blank"></string>

</resources>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="hypatia.friends"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />
<uses-permission
        android:name="android.permission.INTERNET" />
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".HypatiaFriendsActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

The Internet permission is important here, because this application accesses the internet.
<uses-permission
android:name="android.permission.INTERNET" />

Calling a Web Service through Android

2012-02-14T09:52:00.001+05:30

Calling a Web Service using Android

In this post we shall learn how to call a web service using Android.

For this purpose we shall use the Hypatia Quotes Web Service at
http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx

which returns random quotes of Hypatia.

The WSDL for this Web Service is :-

http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx?WSDL

<wsdl:definitions targetNamespace="http://tempuri.org/"><wsdl:types><s:schema elementFormDefault="qualified" targetNamespace="http://tempuri.org/"><s:element name="GetAQuote"><s:complexType/></s:element><s:element name="GetAQuoteResponse"><s:complexType><s:sequence><s:element minOccurs="0" maxOccurs="1" name="GetAQuoteResult" type="s:string"/></s:sequence></s:complexType></s:element></s:schema></wsdl:types><wsdl:message name="GetAQuoteSoapIn"><wsdl:part name="parameters" element="tns:GetAQuote"/></wsdl:message><wsdl:message name="GetAQuoteSoapOut"><wsdl:part name="parameters" element="tns:GetAQuoteResponse"/></wsdl:message><wsdl:portType name="HypatiaQuotesServiceSoap"><wsdl:operation name="GetAQuote"><wsdl:input message="tns:GetAQuoteSoapIn"/><wsdl:output message="tns:GetAQuoteSoapOut"/></wsdl:operation></wsdl:portType><wsdl:binding name="HypatiaQuotesServiceSoap" type="tns:HypatiaQuotesServiceSoap"><soap:binding transport="http://schemas.xmlsoap.org/soap/http"/><wsdl:operation name="GetAQuote"><soap:operation soapAction="http://tempuri.org/GetAQuote" style="document"/><wsdl:input><soap:body use="literal"/></wsdl:input><wsdl:output><soap:body use="literal"/></wsdl:output></wsdl:operation></wsdl:binding><wsdl:binding name="HypatiaQuotesServiceSoap12" type="tns:HypatiaQuotesServiceSoap"><soap12:binding transport="http://schemas.xmlsoap.org/soap/http"/><wsdl:operation name="GetAQuote"><soap12:operation soapAction="http://tempuri.org/GetAQuote" style="document"/><wsdl:input><soap12:body use="literal"/></wsdl:input><wsdl:output><soap12:body use="literal"/></wsdl:output></wsdl:operation></wsdl:binding><wsdl:service name="HypatiaQuotesService"><wsdl:port name="HypatiaQuotesServiceSoap" binding="tns:HypatiaQuotesServiceSoap"><soap:address location="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx"/></wsdl:port><wsdl:port name="HypatiaQuotesServiceSoap12" binding="tns:HypatiaQuotesServiceSoap12"><soap12:address location="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx"/></wsdl:port></wsdl:service></wsdl:definitions>

Out of this document two parts are very important, and I have underlined them:-
1) <soap:operation soapAction="http://tempuri.org/GetAQuote" style="document"/>and

2) <wsdl:operation name="GetAQuote">

The first one becomes the soap action, and the second becomes the method name.
Now, getting to the android part.First of all download the ksoap2-android-assembly-2.6.0-jar-with-dependencies.jar. This file is currently available at :-

http://ksoap2-android.googlecode.com/svn/m2-repo/com/google/code/ksoap2-android/ksoap2-
android-assembly/2.6.0/ksoap2-android-assembly-2.6.0-jar-with-dependencies.jar
Next, add this file to the current project.
1)

Here is the complete project in Eclipse:-

The Activity class in eclipse

HypatiaQuotesClientActivity

package quotes.hypatia;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

import org.ksoap2.SoapEnvelope;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.HttpTransportSE;
public class HypatiaQuotesClientActivity extends Activity implements OnClickListener{
    /** Called when the activity is first created. */
    private Button b;
    private TextView tv;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        b=(Button)findViewById(R.id.button1);
        tv=(TextView)findViewById(R.id.txtQuote);
        b.setOnClickListener(this);

    }
    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        try
        {
        String namespace = "http://hypatiasoftwaresolutions.com";
        String url ="http://hypatiasoftwaresolutions.com/HypatiaQuotesService.asmx?WSDL";
        String soapaction = "http://tempuri.org/GetAQuote";
        String methodname = "GetAQuote";
        SoapObject request = new SoapObject(namespace, methodname);
        SoapSerializationEnvelope envelope =
            new SoapSerializationEnvelope(SoapEnvelope.VER11);

        envelope.setOutputSoapObject(request);
        HttpTransportSE androidHttpTransport = new HttpTransportSE(url);


            androidHttpTransport.call(soapaction, envelope);
            org.ksoap2.serialization.SoapObject resultsRequestSOAP =(org.ksoap2.serialization.SoapObject) envelope.bodyIn;
            int n=resultsRequestSOAP.getPropertyCount();
            tv.setText("" + resultsRequestSOAP.getPropertyAsString(n-1));
        }
        catch(Exception ex)
        {
            tv.setText("" + ex);
        }
    }
}

main.xml

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="quotes.hypatia"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />
<uses-permission
        android:name="android.permission.INTERNET" />
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".HypatiaQuotesClientActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Since, we are calling web services, the internet permission is required:-

<uses-permission
android:name="android.permission.INTERNET" />

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="hello">Random Hypatia Quotes</string>
    <string name="app_name">HypatiaQuotesClient</string>
    <string name="nothing"></string>
    <string name="ButtonText">Hypatia Quotes</string>

</resources>

Here is the output of the program in the emulator:-

Sample output 1

Sample output 2

In the next post of this series, we shall call a web service that requires parameters.

The Web Service running on my Mobile.

Creating & Calling SQL Stored Procedures, SQL Stored Functions through C#

2012-02-08T22:04:00.000+05:30

In this Post we shall learn how to create stored procedures, and functions in MS SQL Server, and also call them from a C# application.

First of all let us create a table

create table scores(Sno int primary key,batsman varchar(50),runs int)

Next we shall create a stored procedure for inserting data into the table:-

create procedure InsertIntoScores(@batsmanname varchar(50) ,@runsscored int)
as
declare @sno int;
select @sno=max(sno) from scores;
if(@sno is NULL)
set @sno=1;
else
set @sno=@sno+1;
insert into scores values(@sno,@batsmanname,@runsscored);

To execute the procedure we shall write

exec InsertIntoScores 'Champak',99

Next we create a function

create function GetScores(@batsmanname varchar(50))
returns int
begin
declare @runs int;
declare @total int;
set @total=0;
DECLARE runs_cursor CURSOR FOR SELECT runs FROM scores WHERE batsman=@batsmanname;
OPEN runs_cursor
FETCH NEXT FROM runs_cursor INTO @runs

WHILE @@FETCH_STATUS = 0
BEGIN
SET @total=@runs+ @total;

FETCH NEXT FROM runs_cursor INTO @runs
END

CLOSE runs_cursor
DEALLOCATE runs_cursor
return @total;
end
The function uses a cursor to loop through the results and add up the scores.Using the sum aggregate query would be better, but I wanted to also provide an example of a cursor.

To test the procedure follow this procedure :-

Next give the value for the parameter

Here is the output:-

To access the procedure from a C# application we need to establish a connection, then create a command object to which we pass the required parameters. For the function we also require a return parameter. Here is how you access the stored procedure:-

System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=smartsystem;Integrated Security=True");
        con.Open();
        System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("InsertIntoScores", con);
        cmd.CommandType = System.Data.CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("batsmanname", "Champak");
        cmd.Parameters.AddWithValue("runsscored", 100);
        cmd.ExecuteNonQuery();

Here is how you access the stored function :-

System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=smartsystem;Integrated Security=True");
        con.Open();
        System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("GetScores", con);
        cmd.CommandType = System.Data.CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("batsmanname", "Champak");
        System.Data.SqlClient.SqlParameter retvalue =new System.Data.SqlClient.SqlParameter("MyRuns",System.Data.SqlDbType.Int );
        retvalue.Direction = System.Data.ParameterDirection.ReturnValue;
        cmd.Parameters.Add(retvalue);
        cmd.ExecuteNonQuery();

        TextBox1.Text = "" + retvalue.Value;

Web Services in PHP

2012-01-21T21:24:00.000+05:30

In this Post, we shall create a Web Service in PHP, and call it through a PHP Client.

The following steps are required before we begin :-

1) Download the file php_soap.dll and copy it into the PHP directory.

Next , make the following entry in the PHP.ini file

In this Web Service we shall create a single function called sayHello

Here is the code for this function :-
function sayHello($name)
{
return "Hello $name";
}

Next create a WSDL file for this function:-

sayhello.wsdl

<?xml version="1.0" ?>
<definitions name="welcome"
targetNamespace="http://localhost:777/HypatiaWebServices/sayHello"
xmlns:tns="http://localhost:777/HypatiaWebServices/sayHello"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<message name="sayHelloRequest">
    <part name="name" type="xsd:string" />
</message>
<message name="sayHelloResponse">
    <part name="return" type="xsd:string" />
</message>
<portType name="QuotePortType">
    <operation name="sayHello">
      <input message="tns:sayHelloRequest" />
      <output message="tns:sayHelloResponse" />
    </operation>
</portType>
<binding name="QuoteBinding" type="tns:QuotePortType">
    <soap:binding
    style="rpc" transport="http://schemas.xmlsoap.org/soap/http" />
    <operation name="sayHello">
      <soap:operation soapAction="" />
      <input>
        <soap:body use="encoded"
        encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" />
      </input>
      <output>
        <soap:body use="encoded"
        encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" />
      </output>
    </operation>
</binding>
<service name="welcome">
    <documentation>Says Hello to you</documentation>
    <port name="QuotePort" binding="tns:QuoteBinding">
      <soap:address
      location="http://localhost:777/HypatiaWebServices/HypatiaWebServiceServer.php" />
    </port>
</service>
</definitions>

Next create the Web Service Server

Here is the code for the server:-

HypatiaWebServiceServer.php

<?php
function sayHello($name)
{
return "Hello $name";
}
$server=new SoapServer("sayhello.wsdl");
$server->addFunction("sayHello");
$server->handle();
?>

Here is the WSDL file as viewed in a Browser:-

Next create a PHP Client. Here we provide the URL to the WSDL.Then simply call the function.The parameters are passed in an array. Here is the complete code:-

HypatiaWebServiceClient.php

<?php
$client=new SoapClient("http://localhost:777/HypatiaWebServices/HypatiaWebServiceServer.php?wsdl");
print $client->__call("sayHello",(array("Champak")));
?>

Here is the output in firefox:-

A Basic Android Database Example

2011-12-15T10:29:00.000+05:30

In this post we shall develop a basic Android Database Example.

Every Android phone contains an inbuilt SQLite database. Therefore, no separate setup or configuration is required.

In this post we shall create a SQLite table, insert some data into it, and also perform a select query.The table contains two fields bookname of type text, and price of type int.
This application contains three buttons Select,Insert and Create for selecting, inserting and creating the table respectively. It also contains two EditBoxes for supplying the Book Name and Price values. There is a TextView for providing status messages.Here is a picture of the User Interface:-

The main classes involved are:-
android.database.sqlite.SQLiteOpenHelper
This class needs to be subclassed to provide for creation of the database.
It has two methods
    @Override
    public void onCreate(SQLiteDatabase database) {
//Called when the database is created.
   }

    @Override
    public void onUpgrade(SQLiteDatabase database, int oldversion, int newversion) {
//Called when the database is upgraded.

    }

android.database.sqlite.SQLiteDatabase
Encapsulates a connection to a SQLite database and provides methods for sending queries to the Database and recovering the result.

android.database.Cursor
This class provides methods for accessing the results of a select query.It can be compared to the java.sql.ResultSet.
Here is the code for the DatabaseHelper

DatabaseHelper.java

package project.hypatia.database;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {
    public DatabaseHelper(Context context) {
        super(context, "hypatiadata", null, 1);
//hypatiadata is the name of the database
// 1 is the version no.
//The null parameter can be used to pass a CursorFactory. We are not using it, so it is null.
        // TODO Auto-generated constructor stub
    }

        @Override
    public void onCreate(SQLiteDatabase database) {
        // TODO Auto-generated method stub


    }

    @Override
    public void onUpgrade(SQLiteDatabase database, int oldversion, int newversion) {
        // TODO Auto-generated method stub

    }

}

This is the code for the ProjectActivity

It contains a subclass DataHandler which contains the click events for the three buttons.

The select button

//*********************************************************************************

if(b.equals(bttnselect))
                {
                    try
                    {
                        String bookname="" + txtBookName.getText();
                        bookname=bookname.replaceAll("'", "''").trim();


                        String[] columns={"Price"};
                        String selection="BookName='"+ bookname + "'";

                    cursor=    database.query("HypatiaBooks", columns, selection, null, null, null, null);

//The Parameters mean

//1) The Name of the Table

//2) A string array containing the fields to be queried.

//3) A string containing the selection criteria

//4) A string array of selection arguments

//5) groupby statement

//6) having

//7) orderby

//The ones not being used are null
                    if(cursor==null)
                    {
                        txtResult.setText("No Data Found");
                        return;
                    }
                    if(cursor.moveToFirst())
                    {
                    int price=cursor.getInt(0);
                    txtPrice.setText("" + price);
                        txtResult.setText("Data Selected");
                    }
                    else
                        txtResult.setText("No Data Found");
                        cursor.close();
                    }
                    catch (Exception ex) {
                        // TODO: handle exception
                        txtResult.setText(ex.getMessage());
                    }
                }

//*********************************************************************************

the cursor provides methods for accessing the data fields, unlike jdbc the indexing starts at 0.

Here is the complete code

HypatiaAndroidProjectActivity.java

package project.hypatia.database;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.database.*;
import android.database.sqlite.*;
public class HypatiaAndroidProjectActivity extends Activity {
    /** Called when the activity is first created. */
    Button bttncreate,bttninsert,bttnselect;
    EditText txtBookName,txtPrice;
    TextView txtResult;

    private Cursor cursor;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        bttncreate=(Button)findViewById(R.id.button1);
        bttninsert=(Button)findViewById(R.id.button2);
        bttnselect=(Button)findViewById(R.id.button3);
        txtBookName=(EditText)findViewById(R.id.txtBookName);
        txtPrice=(EditText)findViewById(R.id.txtPrice);
        txtResult=(TextView)findViewById(R.id.txtOutput);
        DataHandler dh=new DataHandler();
        DatabaseHelper dhh=new DatabaseHelper(this);
       database= dhh.getWritableDatabase();
       bttncreate.setOnClickListener(dh);
       bttninsert.setOnClickListener(dh);
       bttnselect.setOnClickListener(dh);
    }
    //****************************************************************
   SQLiteDatabase database;
    class DataHandler implements OnClickListener
    {

        @Override
        public void onClick(View view) {
            // TODO Auto-generated method stub


                Button b=(Button)view;
                if(b.equals(bttncreate))
                {
                    try
                    {
                        database.execSQL( "create table HypatiaBooks(bookname text primary key,price integer not null )");
                        txtResult.setText("Table Created");
                    }
                    catch (Exception ex) {
                        // TODO: handle exception
                        txtResult.setText(ex.getMessage());
                    }
                }
                if(b.equals(bttninsert))
                {
                    try
                    {
                        String bookname="" + txtBookName.getText();
                        bookname=bookname.replaceAll("'", "''").trim();
                        String price="" + txtPrice.getText();
                        price=price.replaceAll("'","''").trim();
                        database.execSQL("insert into HypatiaBooks values('" + bookname + "'," + price + ")");
                        txtResult.setText("Data Inserted");
                    }
                    catch (Exception ex) {
                        // TODO: handle exception
                        txtResult.setText(ex.getMessage());
                    }
                }

                if(b.equals(bttnselect))
                {
                    try
                    {
                        String bookname="" + txtBookName.getText();
                        bookname=bookname.replaceAll("'", "''").trim();


                        String[] columns={"Price"};
                        String selection="BookName='"+ bookname + "'";

                    cursor=    database.query("HypatiaBooks", columns, selection, null, null, null, null);
                    if(cursor==null)
                    {
                        txtResult.setText("No Data Found");
                        return;
                    }
                    if(cursor.moveToFirst())
                    {
                    int price=cursor.getInt(0);
                    txtPrice.setText("" + price);
                        txtResult.setText("Data Selected");
                    }
                    else
                        txtResult.setText("No Data Found");
                        cursor.close();
                    }
                    catch (Exception ex) {
                        // TODO: handle exception
                        txtResult.setText(ex.getMessage());
                    }
                }
            }



        }




    }

    //****************************************************************

Here is the main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/txtBookName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/txtPrice"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="number"
         />

    <TextView
        android:id="@+id/txtOutput"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/bttncreate" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/bttninsert" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/bttnselect" />



</LinearLayout>

Here is the design view:-

The application in Eclipse

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="hello">Hypatia Basic Android Database </string>
    <string name="app_name">Hypatia Basic Android Database </string>
    <string name="b1">Insert</string>
    <string name="b2">Select</string>
    <string name="bttnselect">select</string>
    <string name="bttninsert">Insert</string>
    <string name="bttncreate">create</string>

</resources>

The APK file can be downloaded at http://hypatiasoftwaresolutions.com/HypatiaAndroidProject.zip

Next, we shall focus on using the Camera in an Android Device.

A Basic Android Animation Example

2011-12-10T10:40:00.000+05:30

In this Post we shall develop a very simple Android Animation Example.
The classes involved are:-

For an explanation of the Graphics classes , please refer the previous post at:-
http://champakonline.blogspot.com/2011/12/basic-android-graphics-example.html
The classes you would find there are View,Canvas,Paint,Path,Bitmap, etc.
Drawing was done by putting the code in the onDraw method of the View class.
You might want a quick review of that post before continuing.

Basic classes for Animation

1) android.view.animation.Animation

This class represents an Android Animation. There are many sub classes of this animation namely:-

a) android.view.animation.ScaleAnimation

b) android.view.animationAlphaAnimation

c) android.view.animation.RotateAnimation

d) android.view.animation.TranslateAnimation;

In this example we implement an animation using AlphaAnimation and RotateAnimation.

Main functionality of the Animation class

The Animation class provides methods for setting the RepeatMode , RepeatCount, Interpolator, setDuration.

RepeatMode: This is the RepeatMode of the Animation. Possible values are Animation.REVERSE,Animation.RESTART.

RepeatCount: Possible values are Animation.INFINITE,Animation.ABSOLUTE.

setDuration(); The value gives the duration of one round of the Animation.

setInterpolator

This method is used to set an Interpolator. We have used an android.view.animation.AccelerateDecelerateInterpolator.
other interpolators are :-
android.view.animation.AccelerateInterpolator,
android.view.animation.AnticipateOvershootInterpolator,
android.view.animation.BounceInterpolator,
android.view.animation.DecelerateInterpolator,
android.view.animation.AnticipateInterpolator,
android.view.animation.CycleInterpolator,
android.view.animation.LinearInterpolator,
android.view.animation.OvershootInterpolator .

We have used the android.view.animation.AccelerateDecelerateInterpolator.
The interpolator decides the progress and restart of the Animation.

The Code:-

HypatiaAnimationView.java

package hypatia.animation.basic;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Path.Direction;
import android.view.View;
import android.view.animation.AlphaAnimation;
import android.view.animation.Animation;
import android.view.animation.Animation.AnimationListener;
import android.view.animation.AnimationSet;
import android.view.animation.RotateAnimation;

public class HypatiaAnimationView extends View implements AnimationListener {
String themessage="Reserve your right to think, for even to think wrongly is better than not to think at all.";
    public HypatiaAnimationView(Context context) {
        super(context);
        paint = new Paint();
        paint.setColor(HypatiaBasicAnimationActivity.colors[HypatiaBasicAnimationActivity.colorno]);
        HypatiaBasicAnimationActivity.colorno=(HypatiaBasicAnimationActivity.colorno + 1) % HypatiaBasicAnimationActivity.colors.length;

        // TODO Auto-generated constructor stub
    }
    Paint paint;//The paint object for the drawing
    @Override
public void onDraw(Canvas canvas)
    {
        super.onDraw(canvas);
            if (hypatiaanimationset == null) {//If the animation set is null, create it
                //***********************Create the Animation Set****************************
                {

                hypatiaanimationset=new AnimationSet(true);
                animation = new AlphaAnimation(1F, 0F);
                animation.setRepeatMode(Animation.REVERSE);
                animation.setRepeatCount(Animation.INFINITE);

                animation.setDuration(5000);
                animation.setAnimationListener(this);
                hypatiaanimationset.addAnimation(animation);
                animation = new RotateAnimation(0, 360,canvas.getWidth()/2,canvas.getHeight()/2);
                animation.setRepeatMode(Animation.REVERSE);
                animation.setRepeatCount(Animation.INFINITE);
                animation.setDuration(1000);
                hypatiaanimationset.addAnimation(animation);

                hypatiaanimationset.setInterpolator(new android.view.animation.AccelerateDecelerateInterpolator());
                startAnimation(hypatiaanimationset);
                }
                //***************************************************************************

        }

        Path circle = new Path();

        int cx = canvas.getWidth() / 2;
        int cy = canvas.getHeight() / 2;
        int r = Math.min(cx, cy);
        paint.setTextSize(48);
        if(HypatiaBasicAnimationActivity.colorno % 2==0)
       circle.addCircle(cx, cy, r-5, Direction.CW);
        else
        circle.addCircle(cx, cy, r-35, Direction.CCW);
        canvas.drawTextOnPath(themessage, circle, 0, 30, paint);
        Bitmap hypatiaportrait = BitmapFactory.decodeResource(getResources(),R.drawable.hypatia);
        canvas.drawBitmap(hypatiaportrait,cx-hypatiaportrait.getWidth()/2,cy-hypatiaportrait.getHeight()/2,null);

    }



    private Animation animation;
private AnimationSet hypatiaanimationset;

    @Override
    public void onAnimationEnd(Animation animation) {
        // TODO Auto-generated method stub

    }
    @Override
    public void onAnimationRepeat(Animation animation) {
        // TODO Auto-generated method stub

        paint.setColor(HypatiaBasicAnimationActivity.colors[HypatiaBasicAnimationActivity.colorno]);
        HypatiaBasicAnimationActivity.colorno=(HypatiaBasicAnimationActivity.colorno + 1) % HypatiaBasicAnimationActivity.colors.length;
        HypatiaBasicAnimationActivity.v.invalidate();
    }
    @Override
    public void onAnimationStart(Animation animation) {
        // TODO Auto-generated method stub

    }
}

HypatiaBasicAnimationActivity.java

package hypatia.animation.basic;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;

public class HypatiaBasicAnimationActivity extends Activity {
    /** Called when the activity is first created. */
static    HypatiaAnimationView v;
static int[] colors={Color.WHITE,Color.YELLOW,Color.MAGENTA,Color.GREEN,Color.RED};
static int colorno=0;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        //This is the first method to be executed

        super.onCreate(savedInstanceState);
         v=new HypatiaAnimationView(this);//Create the view and store it in a static variable for further use
        setContentView(v);//Make this view the current view. This means that whenever the view is invalidated it's onDraw method will be called
    }



}

In the next Post of the series we shall create an Animation using an XML File.

A Basic Android Graphics Example

2011-12-05T10:13:00.000+05:30

In this example we shall explore the basics of drawing in Android. In particular we shall learn the basics of the Paint class , the Canvas class and their methods.We shall also learn how to add pictures as resources, and how to access them.

The OnDraw Method.

This method is the exact equivalent of the paintComponent method in Java. This method is called automatically whenever the View needs to be redrawn. It has a parameter of type Canvas which can be used for drawing on the View. Like the Graphics class in Java the Canvas class provides drawing methods.

The Paint class provides facilities for managing the coloring, the strokes, fonts, and also measurements of Strings. The Bitmap class encapsulates a Bitmap, it also supports drawing.

We start by creating a new Project called Hypatia Drawing Basics

Then import a PNG file into resources

Next subclass the View class. HypatiaDrawingView

public class HypatiaDrawingView extends View {

    public HypatiaDrawingView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }

}

Now create the OnDraw Method inside the HypatiaDrawingView class

@Override
protected void onDraw(Canvas canvas) {
    // TODO Auto-generated method stub
    super.onDraw(canvas);
    Paint paint=new Paint();
    paint.setStyle(Style.FILL);
    canvas.drawPaint(paint);
    paint.setColor(Color.GREEN);
    int width=canvas.getWidth();
    int height=canvas.getHeight();
    int radius;
    if(width<height)
        radius=width/2;
    else
        radius=height/2;



    canvas.drawCircle(width/2, height/2, radius, paint);
    paint.setColor(Color.YELLOW);
    Path ph=new Path();

    ph.setLastPoint(0, height/2);
    ph.lineTo(width/2, height/2+radius);
    ph.lineTo(width, height/2);
    ph.lineTo(width/2, height/2-radius);
    canvas.drawPath(ph, paint);


    Bitmap bruno = BitmapFactory.decodeResource(getResources(),
             R.drawable.giordanobruno);

canvas.drawBitmap(bruno,width/2-bruno.getWidth()/2, height/2-bruno.getHeight()/2,null);
paint.setColor(Color.MAGENTA);
paint.setTextSize(40);
String headline="Hypatia Software Solutions";

float textwidth=paint.measureText(headline);

canvas.drawText(headline,width/2-textwidth/2,height/4,paint);


    }

The methods we have used should basically be self explanatory.

paint.setStyle(Style.FILL); Sets the drawing style. Fill means that closed surfaces are automatically filled.

paint.setColor(Color.GREEN); Sets the drawing color.

paint.setStyle(Style.FILL); Sets the drawing style. Fill means that closed surfaces are automatically filled.

The Path class represents a Polygon. The Last point is also the first point and are automatically joined. Other points are joined serially.

To set the last point we use

ph.setLastPoint(0, height/2);

For other points
ph.lineTo(width/2, height/2+radius); To draw the Polygon
canvas.drawPath(ph, paint);

Drawing the Bitmap

First we access the imported resource.

Then draw it

Bitmap bruno = BitmapFactory.decodeResource(getResources(),
R.drawable.giordanobruno);

canvas.drawBitmap(bruno,width/2-bruno.getWidth()/2, height/2-bruno.getHeight()/2,null);

The last parameter represents the paint object.We are not using it, so it is null.

Here is the complete application as it looks in Eclipse

The Complete Code

HypatiaDrawingBasicsActivity.java

package hypatia.drawing.basics;

import android.app.Activity;
import android.os.Bundle;

public class HypatiaDrawingBasicsActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        HypatiaDrawingView view=new HypatiaDrawingView(this);
        setContentView(view);
    }
}

HypatiaDrawingView.java

package hypatia.drawing.basics;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.Rect;
import android.view.View;

public class HypatiaDrawingView extends View {

    public HypatiaDrawingView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
@Override
protected void onDraw(Canvas canvas) {
    // TODO Auto-generated method stub
    super.onDraw(canvas);
    Paint paint=new Paint();
    paint.setStyle(Style.FILL);
    canvas.drawPaint(paint);
    paint.setColor(Color.GREEN);
    int width=canvas.getWidth();
    int height=canvas.getHeight();
    int radius;
    if(width<height)
        radius=width/2;
    else
        radius=height/2;



    canvas.drawCircle(width/2, height/2, radius, paint);
    paint.setColor(Color.YELLOW);
    Path ph=new Path();

    ph.setLastPoint(0, height/2);
    ph.lineTo(width/2, height/2+radius);
    ph.lineTo(width, height/2);
    ph.lineTo(width/2, height/2-radius);
    canvas.drawPath(ph, paint);


    Bitmap bruno = BitmapFactory.decodeResource(getResources(),
             R.drawable.giordanobruno);

canvas.drawBitmap(bruno,width/2-bruno.getWidth()/2, height/2-bruno.getHeight()/2,null);
paint.setColor(Color.MAGENTA);
paint.setTextSize(40);
String headline="Hypatia Software Solutions";

float textwidth=paint.measureText(headline);

canvas.drawText(headline,width/2-textwidth/2,height/4,paint);


    }
}

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

<string name="hello">Hypatia Drawing Basics Activity!</string>
<string name="app_name">Hypatia Drawing Basics</string>

</resources>

The app as it appears in the emulator.

Next we shall attempt moving graphics.

Image Filters

2011-11-28T22:33:00.000+05:30

This is a continuation of the previous post at Handling Images in C#
A Grayscale Filter
To develop a Grayscale filter simply add up the red green and blue pixels and divide by 3. This averages out the values.

public static Bitmap GrayScaleFilter(Bitmap inputbitmap)
        {

            Bitmap outputbitmap = new Bitmap(inputbitmap.Width, inputbitmap.Height);

            BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            BitmapData outputdata = outputbitmap.LockBits(new Rectangle(0, 0, outputbitmap.Width, outputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int inputstride = inputdata.Stride;
            int outputstride = outputdata.Stride;

            System.IntPtr inputScan = inputdata.Scan0;
            System.IntPtr outputScan = outputdata.Scan0;
            unsafe
            {

                byte* newp1 = (byte*)(void*)inputScan;
                byte* newp2 = (byte*)(void*)outputScan;

                int newOffset1 = inputstride - inputbitmap.Width * 3;
                int newOffset2 = outputstride - outputdata.Width * 3;

                byte redvalue, greenvalue, bluevalue;
                byte newred, newgreen, newblue;
                for (int y = 0; y < inputbitmap.Height; ++y)
                {
                    for (int x = 0; x < inputbitmap.Width; ++x)
                    {

                        bluevalue = newp1[0];
                        greenvalue = newp1[1];
                        redvalue = newp1[2];
                        byte grayscalevalue =(byte )( (redvalue + greenvalue + bluevalue) / 3.0);


                        newp2[0] = grayscalevalue ;
                        newp2[1] = grayscalevalue ;
                        newp2[2] = grayscalevalue ;
                        newp1 += 3;
                        newp2 += 3;
                    }

                    newp1 += newOffset1;
                    newp2 += newOffset2;
                }
            }

            inputbitmap.UnlockBits(inputdata );
            outputbitmap.UnlockBits(outputdata );
            return outputbitmap;

        }

A BlackAndWhite Filter

Simply take the averaged value from the previous filter. If the average is greater than 128 make it white 255 else make it black 255.

      public static Bitmap BlackAndWhiteFilter(Bitmap inputbitmap)
        {

            Bitmap outputbitmap = new Bitmap(inputbitmap.Width, inputbitmap.Height);

            BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            BitmapData outputdata = outputbitmap.LockBits(new Rectangle(0, 0, outputbitmap.Width, outputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int inputstride = inputdata.Stride;
            int outputstride = outputdata.Stride;

            System.IntPtr inputScan = inputdata.Scan0;
            System.IntPtr outputScan = outputdata.Scan0;
            unsafe
            {

                byte* newp1 = (byte*)(void*)inputScan;
                byte* newp2 = (byte*)(void*)outputScan;

                int newOffset1 = inputstride - inputbitmap.Width * 3;
                int newOffset2 = outputstride - outputdata.Width * 3;

                byte redvalue, greenvalue, bluevalue;

                for (int y = 0; y < inputbitmap.Height; ++y)
                {
                    for (int x = 0; x < inputbitmap.Width; ++x)
                    {

                        bluevalue = newp1[0];
                        greenvalue = newp1[1];
                        redvalue = newp1[2];
                        byte avgvalue =(byte )( (redvalue + greenvalue + bluevalue) / 3.0);
                        if (avgvalue > 128)
                            avgvalue = 255;
                        else
                            avgvalue = 0;

                        newp2[0] = avgvalue   ;
                        newp2[1] = avgvalue   ;
                        newp2[2] = avgvalue   ;
                        newp1 += 3;
                        newp2 += 3;
                    }

                    newp1 += newOffset1;
                    newp2 += newOffset2;
                }
            }

            inputbitmap.UnlockBits(inputdata );
            outputbitmap.UnlockBits(outputdata );
            return outputbitmap;

        }

Next we shall develop edge detection filters.

Handling Images in C#

2011-11-27T23:42:00.001+05:30

Image Handling in C#

An Image as we all know is a two dimensional array of pixels. Each pixel has three components Red, Green & Blue. However there is a bit of a surprise here. The first pixel is Blue,the second Green and the last Red. Pixels can be handled directly, however, processing gets very slow. Therefore we shall use pointers. to do this we must use unsafe code. The first requirement is to compile the application with the unsafe switch. Here is how it's done. Open the properties of the project and check the allow unsafe code check box.

First of all we should lock the bitmap using the LockBits method. This is done like this :-

BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

Next we calculate the stride.The stride is the width of a single row of pixels (a scan line), rounded up to a four-byte boundary. If the stride is positive, the bitmap is top-down. If the stride is negative, the bitmap is bottom-up.

int inputstride = inputdata.Stride;

Next we get the address of the first pixel in the bitmap.

System.IntPtr inputScan = inputdata.Scan0;

Next calculate the offset. This is done by

int newOffset1 = inputstride - inputbitmap.Width * 3;

Now we are ready to implement a simple filter. This will simply interchange the Red and Green pixel values and create a new bitmap.

HypatiaFilters.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing.Imaging ;
using System.Drawing ;
namespace PictureFiltering
{
    public static class HypatiaFilters
    {
        public static Bitmap ExchangeRedAndGreen(Bitmap inputbitmap)
        {

            Bitmap outputbitmap = new Bitmap(inputbitmap.Width, inputbitmap.Height);

            BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            BitmapData outputdata = outputbitmap.LockBits(new Rectangle(0, 0, outputbitmap.Width, outputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int inputstride = inputdata.Stride;
            int outputstride = outputdata.Stride;

            System.IntPtr inputScan = inputdata.Scan0;
            System.IntPtr outputScan = outputdata.Scan0;
            unsafe
            {

                byte* newp1 = (byte*)(void*)inputScan;
                byte* newp2 = (byte*)(void*)outputScan;

                int newOffset1 = inputstride - inputbitmap.Width * 3;
                int newOffset2 = outputstride - outputdata.Width * 3;

                byte redvalue, greenvalue, bluevalue;
                byte newred, newgreen, newblue;
                for (int y = 0; y < inputbitmap.Height; ++y)
                {
                    for (int x = 0; x < inputbitmap.Width; ++x)
                    {

                        bluevalue = newp1[0];
                        greenvalue = newp1[1];
                        redvalue = newp1[2];

                        newblue = bluevalue ;
                        newgreen = redvalue ;
                        newred = greenvalue ;

                        newp2[0] = newblue ;
                        newp2[1] = newgreen ;
                        newp2[2] = newred ;
                        newp1 += 3;
                        newp2 += 3;
                    }

                    newp1 += newOffset1;
                    newp2 += newOffset2;
                }
            }

            inputbitmap.UnlockBits(inputdata );
            outputbitmap.UnlockBits(outputdata );
            return outputbitmap;

        }
    }
}

Here is a result of a run of this software

I have put all this in a windows application

Form1.Designer.cs

namespace PictureFiltering
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.p1 = new System.Windows.Forms.PictureBox();
            this.button1 = new System.Windows.Forms.Button();
            this.ofd = new System.Windows.Forms.OpenFileDialog();
            this.p2 = new System.Windows.Forms.PictureBox();
            ((System.ComponentModel.ISupportInitialize)(this.p1)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.p2)).BeginInit();
            this.SuspendLayout();
            //
            // p1
            //
            this.p1.Location = new System.Drawing.Point(32, 12);
            this.p1.Name = "p1";
            this.p1.Size = new System.Drawing.Size(420, 380);
            this.p1.SizeMode = System.Windows.Forms.PictureBoxSizeMode.StretchImage;
            this.p1.TabIndex = 0;
            this.p1.TabStop = false;
            //
            // button1
            //
            this.button1.Location = new System.Drawing.Point(538, 410);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 1;
            this.button1.Text = "Get Image";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            //
            // ofd
            //
            this.ofd.FileOk += new System.ComponentModel.CancelEventHandler(this.ofd_FileOk);
            //
            // p2
            //
            this.p2.Location = new System.Drawing.Point(636, 12);
            this.p2.Name = "p2";
            this.p2.Size = new System.Drawing.Size(420, 380);
            this.p2.SizeMode = System.Windows.Forms.PictureBoxSizeMode.StretchImage;
            this.p2.TabIndex = 0;
            this.p2.TabStop = false;
            //
            // Form1
            //
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(1107, 474);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.p2);
            this.Controls.Add(this.p1);
            this.Name = "Form1";
            this.Text = "Hypatia Picture Filtering";
            ((System.ComponentModel.ISupportInitialize)(this.p1)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.p2)).EndInit();
            this.ResumeLayout(false);

        }

        #endregion

        private System.Windows.Forms.PictureBox p1;
        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.OpenFileDialog ofd;
        private System.Windows.Forms.PictureBox p2;
    }
}

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace PictureFiltering
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ofd.ShowDialog(this);
        }

        private void ofd_FileOk(object sender, CancelEventArgs e)
        {
            p1.Image = System.Drawing.Image.FromFile(ofd.FileName);
            p2.Image = HypatiaFilters.ExchangeRedAndGreen((Bitmap)p1.Image);

        }
    }
}

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

namespace PictureFiltering
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

A Basic Android Example

2011-11-26T22:49:00.001+05:30

A Basic Android Example

Android according to the definition provided at developer.android.com is

a software stack for mobile devices that includes an operating system, middleware and key applications. The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.

It provides the necessary tools for developing software for the Android OS. Important parts are :-

1) SQLLite for Data Storage.

2) Optimized Graphics

3) Media support for common audio/video formats & still image formats.

4) GSM

5) Bluetooth

6) Camera, GPS , etc,

For developing Android applications we need to download the Android SDK, and also setup Eclipse on our computer. Both are available as free downloads. It is also possible to develop using only the Android SDK from the commandline.

Many setup guides are available on the internet, and setting up the environment should be a cinch.

A Sample Application

To begin, let us develop a simple application that shall read two numbers from two textfields and display their sum in the third.

First of all start Eclipse, New Project and select Android Project.

Since we are developing for the Samsung Galaxy, select Samsung Tab.

Android programming is done using the Java Programming Language, and user interface design is done using XML.

To create the user interface .

After creating the project.

Open main.xml

This will bring up the User Interface designer. It has two views. The Graphical Layout & the XML view

Now we shall drag and drop three EditText boxes and a Button onto the mobile.
This is the user interface now.

This is the main.xml file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

    <EditText
        android:id="@+id/editText1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberSigned" >

        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/editText2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberSigned" />

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />

    <EditText
        android:id="@+id/editText3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberSigned" />

</LinearLayout>

We shall change the caption of the button to add.
This is done by adding a new String to
strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="hello">Dedicated to Hypatia of Alexandria</string>
    <string name="app_name">HypatiaBasicAndroid</string>
    <string name="buttoncaption">Add</string>

</resources>

HypatiaBasicAndroidActivity.java

package hypatia.basic;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class HypatiaBasicAndroidActivity extends Activity {
    /** Called when the activity is first created. */
    EditText t1,t2,t3;
    Button b;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        b=(Button)findViewById(R.id.button1);
        t1=(EditText)findViewById(R.id.editText1);
        t2=(EditText)findViewById(R.id.editText2);
        t3=(EditText)findViewById(R.id.editText3);

        b.setOnClickListener(new ButtonHandler());


    }
    class ButtonHandler implements OnClickListener
    {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            try
            {
                int a=Integer.parseInt("" + t1.getText());
                int b=Integer.parseInt("" + t2.getText());
                int sum=a+b;
                t3.setText("" + sum);

            }
            catch (Exception ex) {
                // TODO: handle exception
                t3.setText(ex.getMessage());
            }
            }
        }

    }

In future posts, we shall cover all of android.

Basics of the Genetic Algorithm in Matlab

2011-06-16T22:29:00.000+05:30

Genetic Algorithm Optimization in MATLAB

A genetic algorithm is a population-based optimization method inspired by natural selection. It repeatedly selects promising candidate solutions and creates new solutions using crossover and mutation.

Genetic algorithms can be useful when:

The objective function is nonlinear, discontinuous or difficult to differentiate.
The search space contains several local optima.
Traditional derivative-based methods are unsuitable.

A genetic algorithm is not automatically faster or better than every other optimization technique. The appropriate method depends on the problem. For the linear examples below, linprog would normally be more efficient, but they provide a simple introduction to MATLAB’s ga syntax.

Main components

Fitness function: measures the quality of a candidate solution.
Selection: chooses candidates for reproduction.
Crossover: combines information from selected candidates.
Mutation: introduces controlled random changes.

MATLAB syntax

[x, fval, exitflag] = ga( ...
    fitnessFunction, ...
    numberOfVariables, ...
    A, b, ...
    Aeq, beq, ...
    lowerBounds, upperBounds);

MATLAB expresses linear inequality constraints in this form:

A × x ≤ b

Use empty brackets, [], when an optional constraint is not required.

Problem 1: Minimization with linear constraints

Minimize:

z = −x₁ + 2x₂

Subject to:

−x₁ + 3x₂ ≤ 10
x₁ + x₂ ≤ 6
x₁ − x₂ ≤ 2
x₁ ≥ 0 and x₂ ≥ 0

Fitness function: fitness1.m

function y = fitness1(x)
    y = -x(1) + 2*x(2);
end

MATLAB commands

A = [-1  3;
      1  1;
      1 -1];

b = [10;
      6;
      2];

lb = [0 0];

[x, fval, exitflag] = ga( ...
    @fitness1, 2, A, b, [], [], lb, []);

The solution should be approximately:

x ≈ [2 0]
fval ≈ -2

Genetic algorithms use randomness, so the displayed values may differ slightly between runs.

Problem 2: Converting greater-than constraints

Minimize:

z = 20x₁ + 40x₂

Subject to:

36x₁ + 6x₂ ≥ 108
3x₁ + 12x₂ ≥ 36
20x₁ + 12x₂ ≥ 100
x₁ ≥ 0 and x₂ ≥ 0

MATLAB requires inequalities in the form A × x ≤ b. Therefore, multiply each greater-than constraint by −1:

−36x₁ − 6x₂ ≤ −108
−3x₁ − 12x₂ ≤ −36
−20x₁ − 12x₂ ≤ −100

Fitness function: fitness2.m

function y = fitness2(x)
    y = 20*x(1) + 40*x(2);
end

MATLAB commands

A = [-36  -6;
      -3 -12;
     -20 -12];

b = [-108;
      -36;
     -100];

lb = [0 0];

[x, fval, exitflag] = ga( ...
    @fitness2, 2, A, b, [], [], lb, []);

The solution should be approximately:

x ≈ [3.7647  2.0588]
fval ≈ 157.6471

Important observation

The original third row of matrix A used [-20 -10], although the stated constraint contained 12x₂. It has been corrected to [-20 -12].

Learn With Champak: Experiment with different population sizes, mutation settings and stopping criteria to observe how they affect the quality and speed of the result.

Solving Equations using Matlab

2011-06-14T21:07:00.000+05:30

Equations and Polynomials in MATLAB

Algebra has a long history shaped by Indian, Babylonian, Egyptian, Greek and Persian mathematicians. Brahmagupta made important contributions to arithmetic, algebra and the treatment of zero, while the word algebra comes from the title of Al-Khwarizmi’s work Al-Kitab al-Mukhtasar fi Hisab al-Jabr wal-Muqabala.

Basic rule of equations

An equation remains balanced when the same valid operation is performed on both sides. If LHS = RHS, then:

LHS + x = RHS + x
LHS − x = RHS − x
LHS × x = RHS × x
LHS ÷ x = RHS ÷ x, provided x ≠ 0

Representing a polynomial in MATLAB

MATLAB represents a polynomial using a vector of coefficients arranged in descending powers.

p = [1 0 6 20];

This represents x³ + 6x + 20.

Evaluating the polynomial

Use polyval to evaluate the polynomial for a given value of x.

For x = 1

>> polyval(p, 1)

ans =

    27

For x = 2.5

>> polyval(p, 2.5)

ans =

    50.6250

For the complex value x = 1 + i

>> polyval(p, 1 + i)

ans =

    24.0000 + 8.0000i

Finding the roots

Use the roots function to calculate the roots of the polynomial.

>> roots(p)

ans =

    1.0000 + 3.0000i
    1.0000 - 3.0000i
   -2.0000

The roots can also be stored in a vector:

>> r = roots(p);

Reconstructing the polynomial

Use poly to recover the polynomial coefficients from its roots.

>> v = poly(r)

v =

    1.0000    0.0000    6.0000   20.0000

Plotting the polynomial

Create a vector of x-values, evaluate the polynomial and plot the result.

x = 0:0.01:10;
y = polyval(p, x);
plot(x, y);
grid on;
xlabel('x');
ylabel('p(x)');
title('p(x) = x^3 + 6x + 20');

Multiplying polynomials

Use conv to multiply two polynomials. To multiply the original polynomial by x − 2:

>> product = conv(p, [1 -2])

product =

     1    -2     6     8   -40

The resulting polynomial is x⁴ − 2x³ + 6x² + 8x − 40.

Dividing polynomials

Use deconv to divide polynomials. Dividing the product by x − 2 returns the original polynomial:

>> deconv(product, [1 -2])

ans =

     1     0     6    20

Learn With Champak: Practise these commands by changing the coefficients, evaluating the polynomial at different values and comparing the resulting graphs.

3 D Plots in Matlab

2011-06-11T22:05:00.000+05:30

3 D Plots in Matlab

To create 3D plots , first of all we need to create 3 variables. x,y and z.

Create the x and y arrays:-

>> x=-3:0.25:3;
>> y=-3:0.25:3;

Create the meshgrid:-

>> [X Y]=meshgrid(x,y);

Define:-

Z=sqrt(X.^2 + Y.^2);

mesh(X,Y,Z);

>>surf(X,Y,Z);

>>surf(X,Y,-Z);

>>waterfall(X,Y,Z):-

>>contour(x,y,z):

>>>> surfc(X,Y,Z):-

Now we arrive to the view part:

View is used to give the viewing angle of the plot. the syntax of the command is :-

view(azimuth,elevation);

where the azimuth is an angle measured in degrees in the x-y plane and is measured relative to the negative y axis and positive as always in the anti clockwise direction.

The elevation is the angle measured from the x-y plane in the direction of the z - axis.

default values are azimuth=-37.5 and elevation =35.

Here are the results of applying different views to the last plot:-

>> view(-65,30);

>> view(-37.5,40);

Next we shall move to interpolation using Matlab.

Matrices in Matlab

2011-06-11T09:01:00.000+05:30

Matrices in Matlab

Matrix manipulation is probably the most important part of Matlab. It is what most people will use it for. In this post we shall learn how to create matrices, perform basic manipulations, and to solve simultaneous equations using Matlab.

Creating a Matrix:-

>> a=[1,4,-1;1,1,-6;3,-1,-1];
a

a =

     1     4    -1
     1     1    -6
     3    -1    -1

>>

Transposing the matrix :-

>> a'

ans =

     1     1     3
     4     1    -1
    -1    -6    -1

>>

Inverse of a Matrix:-

>> inv(a)

ans =

    0.0986   -0.0704    0.3239
    0.2394   -0.0282   -0.0704
    0.0563   -0.1831    0.0423

>>

>> a*inv(a)

ans =

    1.0000   -0.0000         0
   -0.0000    1.0000         0
    0.0000    0.0000    1.0000

>> The identity matrix as you would expect.

Now let's try and solve the given equation using Matlab:-

1) x + y + z =9

2)2x - 3y + 4z =13

3)3x + 4y + 5z=40

Create two matrices a & b:-

>> a=[1,1,1;2,-3,4;3,4,5]

a =

     1     1     1
     2    -3     4
     3     4     5

>> b=[9;13;40]

b =

     9
    13
    40

>>

This equation can be represented as

AX=B

=>inv(A) * A * X= inv(A) * B multiplying both sides by inv(A)

=> X=inv(A)* B

>> inv(a)*b

ans =

    1.0000
    3.0000
    5.0000

>>

which means

x=1

y=3

z=5

Now, let's try it the other way round.

The same equation can be represented as X'*A'=B' where ' represents the Transpose.

multiplying both sides by inv(A')

=>X'*A'*inv(A')=B'*inv(A')

=>X'=B'*inv(A')

>> b'*inv(a')

ans =

1.0000 3.0000 5.0000

which means

x=1

y=3

z=5