Night Walker

Fast string concatenation with Groovy

2018-06-04T20:25:00.001+10:00

String concatenation is one of most used functions when coding. With Groovy, there are quite a few approaches. This article will focus on different operators. The code to evaluate the performance is given below.

@Grab('com.googlecode.gbench:gbench:0.3.0-groovy-2.0')
import gbench.*

List turns = ((0..1000) as List)*.toString()
new BenchmarkBuilder().run( measureCpuTime:false ) {
   'Dynamic typing <<=' {
    def nums = ""
    turns.each{nums <<= it}
  }
  
  'Dynamic typing +=' {
    def nums = ""
    turns.each{nums += it}
  }
  
  'Static Typing <<=' {
    String nums = ""
    turns.each{nums <<= it}
  }
  
  'Static Typing +=' {
    String nums = ""
    turns.each{nums += it}
  }
}.prettyPrint()

The results are quite interesting. See below.

Options
=======
* Warm Up: Auto 
* CPU Time Measurement: Off

Dynamic typing <<=   52838
Dynamic typing +=   711659
Static Typing <<=   386825
Static Typing +=    647186

To achieve the best performance, we need to use def to declare a String variable, and use the compound operator <<= to perform the concatenation.

Groovy double blade: safe navigation operator

2018-05-22T21:11:00.001+10:00

In groovy, safe navigation operator is a very cool feature. It helps avoid NullPointerException. However, when using it, need to be careful and avoid something like

list?.size()++

There is no issue for the first part list?.size() at all, the safe navigation operator does it job and helps avoid NullPointerException. The issue is the ++ part. Suppose list is null, list?.size() will also be null. Then null++ will generate an error
“java.lang.NullPointerException: Cannot invoke method next() on null object”.

Portable water storage - best pet food bin

2017-09-30T15:46:00.003+10:00

I was in the market for a dog food container. For this container, one of the main requirements was that it should meet human food grade standards, such as BPA free if the material was plastic, lead free if painted.

Bought a tin with a lid that was specially made for pet food. However, on the second day, ants occupied the tin. So I had to return it. Not quite sure what to buy for dog biscuits, then an idea suddenly popped up, why did I need to focus on pet products? Why not try to find something that was not specially designed for pets, but fitted the purpose?

After a bit search on the hardware shop website, I found one product that was perfect portable water storage with wide mouth: airtight and safe. I ended buying a water storage drum for dog biscuits and it worked well.

Think the problem from another dimension and it may find a better solution.

Microsoft Word/Excel files have weird icons/generic icons

2017-05-23T21:02:00.000+10:00

Not quite sure when it started, but a friend's computer has some strange icons on the desktop. Basically, the icons are the generic icons Windows uses to display the file type it doesn't know how to open. However, when you click on it, they can be opened by Word or Excel.

Upon on further checking, the files with wired/generic icons are actually Word or Excel files. Other Microsoft Office applications don't seem to be affected.

Followed the methods at https://superuser.com/questions/505859/microsoft-word-files-have-weird-icons-suddenly, but nothing helped.

One possible cause of this issue is that the files in the C:\Windows\Installer\{91140000-0011-0000-0000-0000000FF1CE} corrupted. Note that 91140000-0011-0000-0000-0000000FF1CE may change based on your version of Office. You can go to C:\Windows\Installer and search 'wordicon.exe' to locate the exact folder. This folder also can be found in Registry at \HKEY_CLASSES_ROOT\Excel.AddInMacroEnabled\DefaultIcon.

Once you open the folder, find out the *icon.exe files with generic icons, copy the good ones from C:\Program Files (x86)\Microsoft Office\Office14 (again, this may change based on your version of Microsoft Office) and overwrite the ones in C:\Windows\Installer\{91140000-0011-0000-0000-0000000FF1CE}. Restart the computer and the problem should be solved.

Set up Adobe PDF viewer in TeXnicCenter

2017-03-04T22:51:00.003+11:00

After long time without using TeXnicCenter, suddenly found out the PDF viewer does not work any more. It seems that every time when Adobe updates their PDF reader, there are settings that need to be changed in TeXnicCenter.

The first step is to disable "Enable Protected Mode at startup" in the Adobe PDF viewer (Edit>Preferences>General or Edit -> Preferences -> Security(Enhanced), depends on the version). Then change the settings in TexnicCenter.

Basically in the Viewer settings there are four sections that need to be changed. The Executable Path should point to the location where the PDF viewer is . The table below summaries the other settings.

Version	View project's output and Forward search	Close document before running (La)TeX
X	Select DDE command and the command is [DocOpen("%bm.pdf")][FileOpen("%bm.pdf")] Server: arcroviewR10 Topic: Control The server above is for Adobe Reader. For Adobe Acrobat Pro, use arcroviewA10.	Select DDE command and the command is [DocClose("%bm.pdf")] Server: arcroviewR10 Topic: Control The server above is for Adobe Reader. For Adobe Acrobat Pro, use arcroviewA10. If the command does not work, use [AppExit] Instead.
XI	Choose Command line argument and type in "%bm.pdf"	Select DDE command and the command is [AppExit] Server: arcroviewR11 Topic: Control The server above is for Adobe Reader. For Adobe Acrobat Pro, use arcroviewA11.
DC	Use the setting for X or XI. The Server is arcroviewR15 for reader and arcroviewA 15 for Acrobat Pro.	Use the setting for X or XI. The Server is arcroviewR15 for reader and arcroviewA 15 for Acrobat Pro.

Your player is out of date malware

2015-10-02T23:26:00.001+10:00

Suppose your homepage is set as Google. When you open Firefox, it shows the Google as the start-up page, but in addition, there is a popup window of a scary warning:

WARNING! Your (Flash) Player may be out of date. Please update, blah blah…

It may not have the word “Flash”, but the icon next to the warning looks like that it is a Adobe Flash update.

Wait - if you look carefully - you are still at Google page, based on the address bar, but the page looks different from the normal Google page. Now it contains lots of extra links, and the links seem legitimate. However, why it shows the Flash player warning? Google search doesn’t use Flash.

You are right, this is caused by malware. To remove this malware, simply Google “Your player is out of date malware” and follow the advice given.

However, the issue comes back and back again even you have scanned your computer several times using well-known anti-malware software! Don’t panic, it is not your fault. You may forget to check your router, which may be comprised. For example, a strange DNS server is set, or bridge mode is used instead of PPPoE in the modem.

Find out all the necessary information to set your modem/router, do a factory reset, update the firmware if there is a new version available. Set the modem/router and see how it goes.

You may the link below useful:
http://malwaretips.com/blogs/warning-your-flash-player-may-be-out-of-date-virus/

Upgrade Dell XPS 15 L502X to Windows 10

2015-08-01T08:20:00.001+10:00

Yesterday I upgraded my Dell XPS 15 L502X from Windows 7 to Windows 10. The whole process was smooth except a few problems.
Before upgrade, I uninstalled some software I rarely or seldom used.

The Dell Stage should be uninstalled; it is not compatible with Windows 10.
OneDrive should be uninstalled too.
Firewall software should be uninstalled unless it is compatible with Windows 10.

After upgrade, there were a few issues:

No sound: download the latest driver from Dell and reinstall.
No HDMI audio:download the latest driver from NVIDIA and install.
OneDrive not working: probably you have OneDrive installed before upgrade and haven’t uninstalled it before upgrade. In Windows 10, search OneDrive, uninstall the OneDrive (Desktop app), and unlink the account via OneDrive tray icon.
Could not access Internet: the Windows firewall is set to block everything. Change to the default value “Allow” or disable it for now.

Folders without names reappear on desktop

2015-07-01T12:28:00.003+10:00

Recently two folders without names appeared on my desktop. I can delete them, but they will reappear after a while. Furthermore, when I try to delete them, a window pops up and asks

"Are you sure you want to delete these icons from your desktop?
To restore it later, go to Control Panel."

If I open Windows Explorer, go to Desktop, and click on the folder icon without a name, on the bottom left, Windows Explorer displays something like:
0875DCB6-C686-4243-9432-ADCCF0B9F2D7
and
138508bc-1e03-49ea-9c8f-ea9e1d05d65d

This issue may be caused by Office 2013 installation and uninstallation. The following shows the steps to delete these folders completely with the aid of the long names.

Click the Windows Start button, and type in regedit in the search box, then press Enter.
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Desktop\NameSpace and expand the NameSpace branch.
Delete the branches of the same names with the ones found in Windows Explorer.

Now the folders should not reappear by themselves.

Removed user draining battery in Android 5.0 Lollipop

2014-12-16T12:59:00.002+11:00

After you try the guest user mode in Android 5.0 Lollipop and delete it to return your own user profile, you may notice that in the battery usage, there is one item on the top, "Removed user", and the battery usage percentage is increasing.

To solve this problem, the following step may help.

First make sure the use details of the removed user actually do NOT change over time (click on the "Removed user" in the battery status page to see use details). Note that, the battery usage percentage may still be increasing. If the use details change, try to enter into guest mode again, and delete.
When your phone or tablet asks you to recharge, turn off your device, and recharge it.
When the battery is full, turn on your device and the removed user should be gone.

Default reminder not working in Thunderbird Lightning calendar

2014-11-19T12:23:00.002+11:00

You may encounter the problem that the default reminder does not work any more if you access the Google calendar through Provider for Google Calendar in Thunderbird Lightning. Whenever you create a event and use the Default Reminder, it does not work. If you edit that event, you will find the reminder option is set to No reminder. However, in Options --> Calendar --> Alarms, Reminders are set to on for events. Thus it should add a reminder by default. In about:config, you may find similar entries like
calendar.registry.*****-******-******-******-******.settings.defaultReminders
and the value is set to [].

Why the Alarms setting does not work on the Google calendar? This problem occurs because you have NOT set a reminder in Google calendar settings through web interface, and it is inherited to your local computer. To solve the problem, follow the steps below.

Log in to Google Calendar web interface (https://www.google.com/calendar);
Go to Settings -->Calendars and find out the calendars you would like to add a default reminder.
On the right side of the calendar name, click on Edit notifications.
In the Event notifications, add a pop-up notification.
Quit Thunderbird and restart it.

MATLAB: use 'save' in 'parfor' loop

2014-11-17T12:44:00.002+11:00

In the Parallel Computing Toolbox of MATLAB, parfor plays a significant role to speed up the MATLAB simulation. It is not uncommon that we need to save something at the end of each loop. While you want to use save, MATLB will kindly remind you that "SAVE cannot be called in a PARFOR loop". To fix this issue, the save command should be used in a function instead of being called directly in your parfor loop. For example,

parfor m =1:100
 (your code here...)
 save_parfor(mat_file, var1, var2)
end

The mat_file is where the variable data will be saved, and var1, var2 are simply the variables themselves (not their names). Inside the save_parfor function, the save command is called. The complete save_parfor function is given below.

 
function save_parfor(name_mat, varargin)
% save_parfor 
%
%   Inputs: name_mat: where the .mat will be saved, absolute path is
%                     recommended.
%           varargin: the variables will be saved, don't pass on the names of
%                     the variables, i.e, strings.
%
%   Outputs: 
%
%
% EXAMPLE
%
%
% NOTES
% Wenbin, 11-Nov-2014
% History:
% Ver. 11-Nov-2014  1st ed.

num_vars =nargin-1;
name_input =cell(1, num_vars);
for m = 1:num_vars
   name_input{m} =inputname(1+m);
   eval([name_input{m} '=varargin{m};']);
end

save(name_mat, name_input{:});

SmartAudio has stopped working

2014-10-20T19:47:00.001+11:00

SmartAudio is part of Conexant Audio driver. In some cases, when you start your computer, a window may pop up and it tells you that SmartAudio has stopped working. There are lots of people who had this problem. However, the cause and the solution may be different.

If you have tried most of the approaches you can find on the Internet and they all don't work, before you give up, check if the HDMI audio driver that comes with your video card driver has been uninstalled or corrupted. I just fixed an office computer with the SmartAudio issue. It had HDMI audio driver uninstalled and led to the error. Installation of HDMI audio driver from AMD fixed the problem.

K-Lite Codec Pack crashes games when playing in-game videos

2014-05-12T18:53:00.001+10:00

Several months ago, I updated the K-Lite Codec Pack and found out my game would crash when playing in-game videos. At that time, I simply uninstalled the new version, and got back the old version.

Two weeks ago, I decided to give the new version of K-Lite Codec Pack another try, and would like to see the problem has been solved. Unfortunately, nothing changed but crashing games. The FAQ on the official website of K-Lite Codec Pack provides some solutions (http://www.codecguide.com/faq_miscellaneous.htm#item1), but all failed to solve the issue.

What I suspected was that it is related to the configuration of the software. I checked the video format of the games, it is wmv videos. So I did the following.

Opened the Codec Tweak Tool that comes with K-Lite.
Clicked on the Preferred splitters (under the section of Codec and Filter Management)
In the pop up window, there are two columns ## 32-bit source filters ## and ## 64-bit source filters ##.
Found out the .wmv section (both 32-bit and 64-bit sections), changed the setting from Use merit (recommended) to LAV Splitter.

Problem was solved.

***************
Update: Apri 2015
In the recent version of K-lite, you may need to change the VC-1 section instead of wmv. You can use MediaInfo tool that comes with K-lite to find out the detailed information of the game videos.

BD/DVD rom won’t read movie discs, but data discs OK

2014-04-11T23:31:00.001+10:00

I don’t use my BD-rom often, maybe only several times a year. As far as I could remember, last time I had problem with it was almost half a year ago: it failed my three blank DVDs. But I was in a hurry, so didn’t investigate further, and forgot it completely afterwards.
Until today. Didn’t know where the idea came from, I wanted to watch a DVD. The disc was put in, but the BD-rom tried for a few seconds, and then the light went off. As a result, the windows didn’t think there was any disc there.
My first thought was hardware failure. But I highly doubted it. I don’t use it often, and it was working before. Therefore, I tried a data disc, and it worked! So basically I could rule out hardware failure.
Tried to uninstall and reinstall the BD rom, and Microsoft fix it. No luck. The issue still remained unsolved. It didn’t look like a software issue either. Then I came to this post DVD/RW will not read anything. That’s it. I followed the cleaning solution from Naveen:

... and I started cleaning the DVD lens with an ear bud.
When I pressed the lens it was moving in to/fro motion, i moved it left/right couple of time rotated the bud to clean the lens.... and that's it..Life was never the same again ..

The movie finally came alive…

Remove PDF password and restrictions using Ghostscript via drag and drop

2014-03-07T23:08:00.001+11:00

I deal with and process lots of PDFs. However, sometimes the security settings of the PDF documents cause trouble.

There are several online websites available to remove these restrictions. Most offline tools cost more than 20 dollars. Actually we can do this ourselves via drag and drop, if Ghostscript is installed, free of charge.

If you don't have Ghostscript installed, download it from http://www.ghostscript.com/. It is free.

Save the following code as a .cmd file.

@echo off
echo.
echo.
set PATH="C:\Program Files\gs\gs9.07\bin"
echo **************************************
echo.
echo   Start processing, may take a while, please wait.
echo.
echo **************************************
echo.
echo.
set filein=%~1
set fileout=%filein:~0,-4%
gswin64c -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sPDFPassword= -dPDFSETTINGS=/prepress -dPassThroughJPEGImages=true -sOutputFile="%fileout%_noPW.pdf" "%~1"

Change this line according to the installation directory of the Ghostscript on your machine.
```
set PATH="C:\Program Files\gs\gs9.07\bin"
```
Change 'gswin64c' to ‘gswin32c’ if you install the 32-bit version.
Once the configuration is done, you can drag a password protected PDF to the .cmd file icon, a file without restrictions will be generated in the same folder.
To change the icon of the file, create a shortcut to the .cmd file. The icon of the shortcut can be changed.
If the PDF requires a password to open, then this password must be known to remove restrictions. In this case, the password should be provided to gswin64c via
```
-sPDFPassword=YOUR PASSWORD
```
```
 
```
```
  
```

%%%
Update: Apri 2015
If you prefer to use software instead of this DIY approach, you may have a look at PDF Restriction Remover, which can be found at http://www.pdfconvertonline.com/pdf-restrictions-remover.html.

Hangouts in Android shows contact's number instead of name

2014-02-18T14:24:00.002+11:00

Update:

Before you read this article, make sure you have not saved the same number under two contacts. In this case, Google hangouts will not show the name for the number.

I have a friend in USA whose number is +1-***-***-****. Cannot remember when it started, Google hangouts (SMS function) did not show this friend's name anymore. Instead, it showed the number, without the +1 prefix. This friend and the number were in my contact list; all other messages from other contacts were not affected. If I used other SMS apps from Google play store, this issue did not exist. It looked like a bug of Google hangouts.

I followed the solution described at https://productforums.google.com/forum/#!msg/hangouts/h55Ur77xwxc/m0xAWw5BuJkJ, but no luck. After a few tests, I decided to give up on hangouts. Google may have good ideas, but their software is not well made.

However, I would like to dig further. I used SMS backup & restore app to backup all my messages. Then downloaded them to my computer and checked the messages from the friend. At that time, I thought I might be able to solve the problem.

Because of unknown reasons, two of the messages between my friend and me used the number ***-***-**** instead of +1-***-***-**** . Since I was in Australia, how it could happen still puzzled me. Furthermore, hangouts thought ***-***-**** and +1-***-***-**** were not equal, but still grouped the messages together.

I changed the number to the +1 format, uploaded the file back to my phone, erased all SMS on the phone, and then restored the messages using the SMS Backup & Restore app. Finally buggy hangouts showed my friend's name, not the number.

Relaxing music: Indescribable Night - Kate St.John 720p HD

2014-01-13T14:26:00.001+11:00

This is Indescribable Night from Kate St. John (Album: Indescribable Night). Her beautiful voice calms you down.

Click below to buy the album from Amazon
Indescribable Night
Kate St. John

Dell QuickSet error

2013-11-22T15:37:00.001+11:00

I haven’t used the Dell configuration key for a while. Today I accidentally touched it, and an error popped up:

Error found! Submit this issue to QuickSet owner!

Based on this post, this issue is caused by Intel® PROSet/Wireless Software for Bluetooth® technology with version above 3. So I uninstalled the Intel® PROSet/Wireless Software for Bluetooth® technology 3.0.1304, and installed version 2.6.1212 back (which can be downloaded here http://www.intel.com/support/wireless/wtech/proset-ws/sb/CS-034060.htm). It is all good now.

MATLAB: Can't load libmwmathlinalg.dll

2013-11-04T13:26:00.001+11:00

When I ran MATLAB scripts on my computer, the following error was given

Warning: File: finfo.m Line: 157 Column: 41

The expression on this line will generate an error when executed. The error will be: Can't load 'C:\Program Files\MATLAB\R2013a\bin\win64\libmwmathlinalg.dll': Error performing inpage operation.

> In open at 132
In uiopen at 196

This was strange, because libmwmathlinalg.dll was in the given directory. The lazy solution to this issue is to reinstall MATLAB.

LaTex: customise IEEEtran bibliography style with multibib package

2013-07-17T13:57:00.001+10:00

When using multibib package, I wanted to apply and customise the IEEEtran bibliography style. It should be similar with bibentry. However, it did not work. The function that repeated names of entries are replaced with dashes were disabled, but results showed that the dashes were still there. Searched the Internet but could not find a solution. OK, it’s time to debug.

Use LaTex multibib package

First, load the package using

\usepackage{multibib}

Then, in the preamble define new cite and bibliography commands through providing suffixes. For example

\newcites{jourl,conf}{{Journals},{Conferences}}

This command here gives two suffixes: jourl and conf. Therefore, we have the following new commands

\citejourl
\nocitejourl
\bibliographystylejourl
\bibliographyjourl

and

\citeconf
\nociteconf
\bibliographystyleconf
\bibliographyconf

When the commands with “jourl” are used, all the references will be put under the reference list, of which the name is “Journals” as defined in the \newcites command.

When the commands with “conf” are used, all the references will be put under then reference list, of which the name is “Conferences” as defined in the \newcites command.

When the document is compiled, there will be two auxiliary files: jourl.aux and conf.aux. These two files need to be compiled through BibTex.

Use IEEEtran bibliography style

Suppose the pub.bib file contains the entry

@ieeetranbstctl{BSTcontrol,
        CTLdash_repeated_names = {no},
        CTLuse_alt_spacing = {no}}

To apply this control entry to the “Journals” reference list, we should call

\bstctlcite[@auxoutjourl]{BSTcontrol_Thesis}
\bibliographystylejourl{ieeetran}
\bibliographyjourl{pub}

Note that there is an optional argument in the \bstctlcite command which includes the suffix “jourl”. To control the "Conferences" list, simply change the optional argument accordingly.

Count the frequency of elements in a vector or matrix- part 3

2013-06-21T09:36:00.001+10:00

Option 5: arrayfun

counts5 = arrayfun( @(x)sum(M==x), unique(M) );

“A = arrayfun(fun, S) applies the function specified by fun to each element of array S, and returns the results in array A.” This approach is quite straightforward. The following is an example.

M = [1; 2; 6; 2; 6]; 
counts5 = arrayfun( @(x)sum(M==x), unique(M) )

counts5 =

     1
     2
     2

Option 6: bsxfun

counts6 = sum( bsxfun(@eq, M, unique(M)') )';

The function “bsxfun” applies element-by-element binary operation to two arrays. Though this method is not hard, but it is easier to understand if we do it step by step.

M = [1; 2; 6; 2; 6];
unique(M)'

ans =

     1     2     6

bsxfun(@eq, M, unique(M)')

ans =

     1     0     0
     0     1     0
     0     0     1
     0     1     0
     0     0     1


counts6 = sum( bsxfun(@eq, M, unique(M)') )'

counts6 =

     1
     2
     2

Option 7: sparse

counts7 = full(sparse(M,1,1));

Again, for this approach, we need to check the MATLAB help file first. “S = sparse(i,j,s,m,n,nzmax) uses vectors i, j, and s to generate an m-by-n sparse matrix such that S(i(k),j(k)) = s(k), with space allocated for nzmax nonzeros. Vectors i, j, and s are all the same length. Any elements of s that are zero are ignored, along with the corresponding values of i and j. Any elements of s that have duplicate values of i and j are added together.” An example is given below.

sparse(M,1,1)

ans =

   (1,1)        1
   (2,1)        2
   (6,1)        2

counts7 = full(sparse(M,1,1))

counts7 =

     1
     2
     0
     0
     0
     2

Part 1: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or.html
Part 2: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or_20.html
Part 3: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or_21.html

References:
1 MATLAB help file.
2 http://stackoverflow.com/questions/2880933/how-can-i-count-the-number-of-elements-of-a-given-value-in-a-matrix

Count the frequency of elements in a vector or matrix- part 2

2013-06-20T10:07:00.001+10:00

Option 3: accumarray

counts3 = accumarray(M, ones(size(M)), [], @sum);
% or simply: accumarray(M, 1);

This approach is not easy to understand. Let’s see what the function accumarry does first. MATLAB help file states that “accumarray groups elements from a data set and applies a function to each group. A = accumarray(subs,val) creates an array A by accumulating elements of the vector val using the elements of subs as indices. The position of an element in subs determines which value of vals it selects for the accumulated vector; the value of an element in subs determines the position of the accumulated vector in the output”.
So what does it mean exactly? Let’s see an example.

subs = [1; 2; 4; 2; 4];
val = ones(1,5);
A = accumarray(subs, val)

A =

     1 % A(1) = val(1) = 101
     2 % A(2) = val(2)+val(4) = 1+1 = 2
     0 % A(3) = 0
     2 % A(4) = val(3)+val(5) = 1+1 = 2

Thus, when we set the input argument “val” as an array of all ones, the function accumarray actually counts the frequency of each element in the first input.

Option 4: sort/diff

[MM idx] = unique( sort(M) );
counts4 = diff([0;idx]);

This approach first finds out the unique element in the input vector, then use “diff” to find out the frequency of each elements. Again, an example is a good way to learn.

M = [1; 2; 4; 2; 4; 5; 2]; % input is a column vector
[MM idx] = unique( sort(M) )
MM =

     1
     2
     4
     5


idx =

     1
     4
     6
     7

counts4 = diff([0;idx])

counts4 =

     1
     3
     2
     1

In the first step of the approach, “unique” is applied on the sorted input. The returned indexes of the unique elements contains the information of the frequency. Then “diff” is used to extract the frequency information. Note that the input is a column vector. If it is a row vector, in the last step, it should be

counts4 = diff([0 idx])

Count the frequency of elements in a vector or matrix- part 1

2013-06-04T11:30:00.001+10:00

In MATLAB, it is a common task that find out how many time an element that appears in a vector or matrix. If the element is known, the intuitive idea that comes up in my mind is to use the following code

M = randi([1 5], [5 3]); % M is the matrix
sum(sum(M ==2)); % 2 is the element to be counted

However, sometimes we want to count all the elements in a matrix or a vector, what should we do? Amro has given several approaches to count the elements without detailed explanation. I think the best way to learn is to understand why we use the code. Thus in the following, explanations are given for the approaches by Amro.

Option 1: tabulate

t = tabulate(M); % frequency count for a vector
counts1 = t(t(:,2)~=0, 2); % find out the frequency of all the elements existing in the vector

TABLE = tabulate(x) creates a frequency table of data in vector x. Information in TABLE is arranged as follows:

1st column — The unique values of x

2nd column — The number of instances of each value

3rd column — The percentage of each value

However, this approach requires MATLAB Statistics Toolbox and the input must be a vector.

Option 2: hist/histc

counts2_1 = hist( M, numel(unique(M)) );
counts2_2 = histc( M, unique(M) );
% unique: find unique elements of vector
% numel: mumber of elements in array

n = hist(Y,x) where x is a vector, returns the distribution of Y among length(x) bins with centers specified by x.

n = histc(x,edges) counts the number of values in vector x that fall between the elements in the edges vector (which must contain monotonically nondecreasing values).

Note the difference between the use of hist and histc.

Part 1: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or.html
Part 2: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or_20.html
Part 3: http://nw360.blogspot.com.au/2013/06/count-number-of-elements-in-vector-or_21.html

References:
1 MATLAB help file.
2 http://stackoverflow.com/questions/2880933/how-can-i-count-the-number-of-elements-of-a-given-value-in-a-matrix

Modify font size when using FncyChap package

2013-04-08T13:44:00.001+10:00

The latex package FncyChap provides several nice pre-defined style for chapter headings. However, I found out the chapter title takes too much space sometimes; it may take more than two thirds of the page. Thus, it is necessary to reduce the font size for the chapter title.
The first step is to find out what is the default value in the pre-defined layout, which can be found in the FncyChap document. Take the ‘Lenny ’ style as an example. The default settings for the chapter title is

\ChTitleVar{\Huge\bfseries\rm}

To change the title size from ‘\Huge’ to other values, in the preamble, add the following

\makeatletter

\ChTitleVar{\huge\bfseries\rm}

\makeatother

Now the font size is smaller and suitable for long chapter titles.

Modify the space between MATLAB subplots

2013-01-30T14:25:00.001+11:00

Sometimes, the MATLAB function subplot reserves too much space and destroys the appearance of the plot. Therefore, it is necessary to adjust the space between the subplots and between the subplots and the boarder.
The subplot function itself provides the command:

subplot('Position',[left bottom width height])

It creates an axes at the position specified by a four-element vector. Note that they are in normalized coordinates in the range from 0.0 to 1.0. If only minor change of the space is required, this approach is appropriate. The following is an example showing how to increase the width of the subplot.

h = subplot(2,3,2);
p = get(h, 'position');
p(3) = p(3) + 0.02;
set(h, 'position', p);

However, the adjustment of one subplot may affect other plots. Thus it is a good idea to have a general subplot arrangement beforehand. In this situation, we can use axes to create the axes graphics object. The function axes accepts the four-element vector as its position.

axes('Position',[left bottom width height])

Pekka Kumpulainen has published a “tight subplot” function to MATLAB File Exchange. It gives you the control of subplot spacing. The file can be found at http://www.mathworks.com/matlabcentral/fileexchange/27991.