Matlab Tips

• Before invoking...
  • Matlab Helpdesk
  • Matlab directry
  • Nice command
  • Emacs lisp
  • Running background
  • Data Clip
• String tips
  • Combine two strings
  • Making file name
• Transfer function
  • Getting NUM and DEN from 'tf format
• File I/O
  • Input your file name
• FFT Tip
  • FFT Calculation
• Figure Tip
  • index of subplot: (a), (b), ...
  • Prime (')
• CMEX Tip
  • Debug

Before invoking ...

Matlab Helpdesk

I don't believe this info is not so popular in ECE/ORST but you can access Matlab helpdesk in ECE. Matlab Helpdesk is a place which has all help files in HTML and the manual in PDF

1. Go to ECE Computing page
2. Choose "Matlab documentation".
3. You will be asked user name and password. Those are the same as the login name and the password of ECE network. This may be stored in cockies and you may not be asked again. Yod don't know what cockies are? Never mind. :-)
4. Once after you could acess it, you will find help desk here.
5. Again it has manuals in PDF under each toolbox ref.

Usefull pages:

• Signal Processing Toolbox
• Signal Processing Toolbox Manual in PDF
• Control System Toolbox
• Control System Toolbox Manual in PDF

In this case, you don't need any membership, of course, if you're in ECE.

Your matlab directry

You can put your favorite function in your matlab directry under your home directry. Matalb search your ~/matlab when you invoke matlab automatically.

Be nice!

ECE recommends us to use "nice" command with matlab. I have the alias in my .cshrc.user file.
alias mat 'nice matlab'

For emacs lover

You can download an emacs lisp of the matlab-mode from Mathworks web site.

Running in background

You can run your M-file in your shell script with redirection method. Consider this when you need, especially mid-night working. :-)

% nice matlab < foo.m > result.txt

More info in Mathworks.

Data clip

Some hints are in Mathworks web site. But I would use awk/sed to create a pure data file.

String Tips

Combine two strings

       
       ss1='str1';
       ss2='str2';
       ss3=[ss1 ss2]

       smat=[{ss1}, {ss2}, {ss3}]
       
       

Making the file name which has string + number

       
       %
       clear
       %string test
       ss1='str1';
       ss2='str2';
       ss3=[ss1 ss2]
       
       smat=[{ss1}, {ss2}, {ss3}]
       
       for m=1:3
         ff1=sprintf('str_test%d',m);
         fid=fopen(ff1,'w');
         fprintf(fid,'This file is for %s\n',smat{m});
         fclose(fid);
       end
       

Transfer function

Getting NUM and DEN from 'tf' format

       [NUM, DEN]=tfdata(H);
       HB=NUM{1}; HA=DEN{1};
       

Alternatively and simply,

       [HB, HA]=tfdata(H, 'v');
       

(thanks to Péter)

File I/O

Input your file name

       celar all
       R = input('What is the data file name? : ', 's')
       dd = load (R);
       % you need '(' and ')'. That's a tip!
       in1 = dd(:,1);
       ...
       

FFT Tips

FFT calculation

We have to multiply some coefficient to adjust the result of MATLAB fft.

       Sample code to get the correct power:
       
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% initialization
       N = 1024;		% Total number of samples
       As = 1;			% Signal amplitude
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Sine signal
       st = As * sin(2*pi*100*[0:N-1]./N);
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% fft
       Sf = fft(st);
       Sf = Sf .* conj(Sf);
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Normalization
       % * 2 is for imaginary and real freq.
       % N^2 to get -3dB for the amplitude of one
       Sf = Sf * 2 / N^2;		
       plot(10*log10(Sf)); grid
       
       

Figure Tip

Index of subplot: (a), (b), ...

Under the xlabel, the index of subplot is sometimes needed, which means (a), (b), and so on. It was very easy. Try

xlabel({'frequency in Hz';'(a)'})

For more info, please refer this. Solution Number: 1405 How can I place a two-lined title, x-label, y-label, or z-label on my plot?

How to use " ' " in the figure title

Matlab complains if you use the " ' " character. I'm cheating. Try LaTeX \prime command instead of typing " ' ". For example,

title('This is Kajita{\prime}s plot')

CMEX Tip

Debug

I don't get the solution yet. But you may refer to Tech Note: 1608 and thisin Mathworks. Then, tell me how to do that, when you find out...

Here is what I am trying so far:

1. Compile C-Mex code using
   % cmex -g foo.c
2. Run matlab with the option:
   % matlab -Dgdb
3. Use run command in the debugger:
   (gbd) run
4. There are lots of messages on the screen and it stopped.
5. Enforce the debugger in the front:
   % fg
6. Press to continue.
7. Matlab opening window is shown, but stopped again.
8. Type run again:
   (gbd) run
9. Type y to start it from the beginning.
10. Type to continue.
11. Now I get Matlab prompt.
12. Enable MEX-file debugging:
    >> dbmex on

Last modified: Thu Oct 19 11:48:11 2000