Learning Yourself Matlab

In MATLAB figure, how to change the X or Y axis ticks or labels?

2012-07-06T08:23:00.001-07:00

A default case is the following where I plot 100 random numbers

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
var=rand(1,100);
figure; plot(1:100,var,'--rs');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

In X axis, the labels are placed 10 places apart.....0....10....20....30..... like that....If I want to have labels 2 places apart 1...3...5....7 till 100 how may I do it?

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

set(gca,'XTick',1:10:100) % Here gca refers to the handler of the current figure's axis

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Now, try to do the same in Y-axis! Share your result :)

How to save/print MATLAB figure in a file?

2012-07-05T07:14:00.001-07:00

Imagine I want to print/save a matlab figure into disk. May be I want to save it in PNG format. How do I do that?
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

file_handler=figure;
plot(randn(10,1));
print(file_handler,'-dpng', 'my_file_name.png');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Check your current folder. A file named my_file_name.png should be there!

How to print variable value in title of a matlab figure?

2012-07-05T07:06:00.000-07:00

Imagine my MATLAB figure has a title where I want to print the value of a variable. How can I do that ?

for var=1:3
figure;
plot(randn(10,1)); title(['rand number=: ' num2str(var) ]);
end
%%%%%%%%%%%%%%%%%%Out Put%%%%%%%%%%%%%%%%%%%%%%%%%%

Multiple Legend in plot/subplot

2012-07-05T03:17:00.001-07:00

I needed multiple legend on a plot for multiple data where data sizes were different. If try classical legend you get the following

figure
p1=plot(I_test(:,:,1),I_true(:,:,1),'r.');
hold on
p2=plot(RGB_test(:,1),RGB_ref(:,1),'g.');
legend( 'true','calculated');
It does not give what I want !! Therefore.....continue reading..

Instead try the following to have different legend

figure
p1=plot(I_test(:,:,1),I_true(:,:,1),'r.');
hold on
p2=plot(RGB_test(:,1),RGB_ref(:,1),'g.');
legend([p1(1) p2(end)], 'true','calculated');

Legend in Subplot

2012-07-05T02:27:00.002-07:00

Acknowledgement : here
subplot(2,2,1);
ph1=plot(rand(10,2),'s-');
subplot(2,2,3:4);
ph2=plot(rand(10,3),'o-');
sh=subplot(2,2,2);
p=get(sh,'position');
lh=legend(sh,[ph1;ph2]);
set(lh,'position',p);
axis(sh,'off');

Matlab: legend in Errorbar

2012-03-12T13:45:00.001-07:00

I want to generate an error bar like this. Here, I am comparing three algorithms and I need three legends. Here is how I did it

y = [2.22153808961105 2.49790518623828 2.78257964160148]; % mean or average
e = [0.539408440954881 1.23204940330217 0.813491394996712]; % 1 standard deviation
figure
errorbar(y,e,'r.');
hold on;
h=plot(1,y(1),'ro',2,y(2),'go',3,y(3),'bo');
legend(h,'feature','feature3x3','cluster','Location','Best');

In Matlab : Sorting by indexes of another sorting

2012-02-24T06:30:00.001-08:00

Imagine, we have the following two array of numbers
A=[ 2 4 6 7 8 8];
B=[ 5 8 2 5 0 5];
Problem:
---------
we want to sort A and then arrange B according to the index of A.

Solution:
----------

>> [sortedA,indexA]=sort(A)

sortedA =

2 4 6 7 8 8

indexA =

1 2 3 4 5 6

>> B(indexA)

ans =

5 8 2 5 0 5

How to append in a excel file using Matlab?

2012-02-16T15:39:00.001-08:00

Imagine that I have the following excel file called "algoperformace.xls"

algoName	mode	95percentile	max	mean
Algorithm1	13.15153679	20.03323188	39.52043729	15.65858

Now, I would like to add a new line as the following into this excel file using matlab

Neighbor

2.721678458

5.536962451

26.63633753

3.858783

How to do that?
----------------------------------------------------------------------------------
Answer:
%% Loading the excel into matlab

[~, ~, alldata] = xlsread('algperformace.xls');
% We will add new entry line into 'alldata' variable and then will write the excel file
% The script will compute the value for algoname, mode, color_diff_95_percentile, max, mean
% adding those values into the cell of 'alldata'
alldata(size(alldata,1),:)={algoname, mode, color_diff_95_percentile, max, mean};
%writing the complete new 'alldata' into the same excel file
xlswrite('algperformace.xls', alldata);

Try your own example :)

How may I make the user to browse and select file in Matlab

2012-02-02T05:38:00.000-08:00

Very often, Matlab programs need to specify input files or images. Instead of giving the absolute path to that file we may make the user to browse and locate the file.

uigetfile is the function that can do that job. Here is an example.

disp('Select the Reference view');
[filename_ref,pathname_ref] = uigetfile('*.*','Select the Reference view');
if isequal(filename_ref,0)
disp('User selected Cancel')
else
disp(['Reference view: ', fullfile(pathname_ref, filename_ref)])
end

How to use binary variable/ TRUE FALSE in MATLAB?

2011-12-15T02:09:00.000-08:00

You know in C++ you may write the following

bool binary_variable=TRUE; // Or FALSE

But How to do that in MATLAB?

>>true([m, n])
This will create an m-by-n matrix of binary (logical) ones // TRUE
>>false ([m, n])
For m-by-n matrix of binary (logical) zeros // FALSE

In MATLAB: find two tailed P value of t-distribution (Student's t-distribution)

2011-12-14T07:42:00.000-08:00

Problem:
-----------
Given the t-ratio and the degrees of freedom(dof), find two tailed P value of t-distribution (Student's t-distribution)

Solution:
---------
Using the econome trics toolbox here is an example where t ratio = 2.2000 and degree of freedom= 5 ; The computed two tailed P Value is 0.0791

tdis_prb

function y = tdis_prb(x,n)
% PURPOSE: calculates t-probabilities for elements in x-vector
%---------------------------------------------------
% USAGE: y = tdis_prb(x,n)
% where: x = vector containing computed t-values
%        n = degrees of freedom parameter
%---------------------------------------------------
% RETURNS:
%        y = a vector of marginal probability levels
% --------------------------------------------------
% SEE ALSO: fdis_prb(), chis_prb
%---------------------------------------------------

% written by:
% James P. LeSage, Dept of Economics
% University of Toledo
% 2801 W. Bancroft St,
% Toledo, OH 43606
% jpl@jpl.econ.utoledo.edu


if nargin ~= 2; error('Wrong # of arguments to tdis_prb'); end;
if n <=0; error('dof is negative or zero in tdis_prb'); end;

x2 = n./(n+x.^2);
one = find(x2 >= 1);
if length(one) > 0
    x2(one,1) = 1-1e-12;
end;
zip = find(x2 <= 0);
if length(zip) > 0
    x2(zip,1) = 1e-12;
end;

tmp = 1.0 - 0.5*betainc(x2,0.5*n,0.5);
y = 2*(1-tmp);
x
n
end

x =

    2.2000


n =

     5


ans =

    0.0791

Exercise:
-----------
Using this function (tdis_prb) plot results for [-4:0.05:4] for 10 degrees of freedom.

In MATLAB: Sort an Array and then Undo that sort

2011-12-13T09:49:00.000-08:00

PROBLEM:

--------------

Imagine I have an array to be sorted and after I sort it I want to UNDO that sort so that the array came back to the initial condition.

How?

---------

A=[10 9 7 4 5 7 5 3 ];

>> [SORTED_A,IX]=sort(A)

SORTED_A =

3 4 5 5 7 7 9 10

IX =

8 4 5 7 3 6 2 1

>> UNSORTED=1:length(A)

UNSORTED =

1 2 3 4 5 6 7 8

>> NEW_INDEX(IX)=UNSORTED

NEW_INDEX =

8 7 5 2 3 6 4 1

>> NEW_A=SORTED_A(NEW_INDEX)

NEW_A =

10 9 7 4 5 7 5 3

>> isequal(A,NEW_A)

ans =