246 Church Street, Suite 307
    New Haven, CT  06510
    Tel: 203-777-7442
    Fax: 203-776-4074

    ???
    ???
    ???

    Cochituate Place
    24 Prime Park Way
    Natick, MA 01760
    Tel: 508-653-1415
    Fax: 508-653-2997.
    Email: info@mathworks.com

    Harmonic Software, Inc
    12223 Dayton Avenue North
    Seattle, WA 98133
    Tel: 206-367-8742
    Fax: 206-367-1067
    Email: harmonic@world.std.com

    sunsite.unc.edu://pub/Linux/apps/pv-wave

    1700 Westlake Ave. N.
    Suite 500
    Seattle, WA 98109
    Tel: 206-283-8802
    Fax: 206-283-6310

    There is a very active user group (of mainly statisticians) 
    with a mailing list that can be found in the FAQ.

    FAQ: http://www.stat.math.ethz.ch/~roosen/S-faq_toc.html
         ftp.stat.math.ethz.ch  in  /pub/Doc  as  S-faq.*
    see also ftp://netlib.att.com/netlib/att/stat/info/proj.html

    3260 Jay St.
    Santa Clara, CA  95054-3309
    Tel: (408) 980-1500
    Fax: (408) 980-0400
    Email: xmath-info@isi.com
    WWW: http://www.isi.com     

==== Then we have the non-commercial ones in alphabetical order. ====

Check out the following page too, it is probably more complete on this point.

http://www-ocean.tamu.edu/~baum/graphics-analysis.html

==== Properties of some of the free programs. ====

The following is compiled from the net.

                    RLaB   Octave   SciLab   Tela
      DOS version    +      -        -        -
    documentation    +      +        -        ?
             fast    +      -        ?        +
Matlab compatible    -      +        -     converter

from sundaram@news.cig.mot.com (Divya A. Sundaram) ... I am running Octave and SciLab under Linux (and also have matlab on the Windows box and on the Macintosh). I find Octave to be quite suitable for MOST stuff I used to do under Matlab (and find that most commands and syntax are the same or VERY similar). SciLab is something else. It is absolutely amazing and I have decided to spend some time learning it more thoroughly. I feel (personal opinion only) that it is a FAR more complete system than Octave or Matlab 4.0.

==== A proposed standard ====

There is an IFAC/IEEE-CSS Working Group developing standards and guidelines for these tools. A proposed standard command language was developed, is described in the document "Command Language Standard for CACSD Software" and is available from

    Magnus Rimvall
    Control Systems Laboratory, GE-CRD
    Schenectady, NY 12301

[4] Are there any Matlab programs that do XYZ?

A nice function is LOOKFOR, with the help of which you can search for a Matlab function with a keyword on your own computer. If there isn't there might be in one of The Mathworks' toolboxes, if you don't have them all. The Mathworks' toolboxes are the following, on which you can find more information at The Mathworks site.

For graphics check out a web page that lists and provides descriptions and links to many freely available data analysis and graphic pages on the net:

       
http://www-ocean.tamu.edu/~baum/ocean_graphics.html

Some major interesting matlab tools are the following.

[5] What books and papers are there?

At The Mathworks site there are m-files that are used in the following books. The authors and full titles et c are also at The Mathworks site.

There are at least some Matlab introductions on the net;

[6] Is there any automatic Matlab to C converter?

Mathworks is now selling its translator. Another alternative is MATCOM, which is a is freeware translator of MATLAB to C++. It seems to work pretty well, but can be confused by feval and gives up on eval. C++ compiler (Borland C++/Visual C++/DJGPP) on a PC compatible is required, or a UNIX system. For Borland C++/Visual C++ Windows is needed.

Home Page (now) -
  http://techunix.technion.ac.il/~yak/matcom.html
Mirrors (in a few days) -
  http://rio.esm.vt.edu/mirror/matcom
  ftp://ftp.eeng.dcu.ie/pub/matlab/MATCOM
  ftp://ftp.funet.fi/pub/sci/math/matlab

[7] When will Matlab for Linux arrive?

Matlab 4.2c for Linux is released and selling!

   sunsite.unc.edu://pub/Linux/apps/math/matrix   
   sunsite.unc.edu://pub/Linux/apps/pv-wave

Well, use GRIDDATA. However, since this is unlikely to work read what Kirill Pankratov says:

[9] What about undocumented functions in Matlab?

from Cleve Moler ...

set(0,'HideUndocumented','no')

[10] What is this `system_dependent' function?

from John Little (w/editing) ...

  system_dependent(1)     deals with the MATLAB-ACSL interface. 
                          ACSL is a simulation language that 
                          MATLAB can talk to. See ACSL.M for 
                          more information.

  system_dependent(2,0)   turns off command-line editing.
  system_dependent(2,1)   turns it back on.

  system_dependent(3)     is unused.

  system_dependent(4,i,j) is used to program the command-line 
                          editing keys. See CEDIT.M for more 
                          information.

  system_dependent(5)     enables core dumps in the event of seg 
                          faults. Normally MATLAB tries to catch 
                          seg faults and "continue".

From Andreas Payer (payer@cipserv1.physik.uni-ulm.de): The problem is, that MATLAB resets the printer driver back to its 'DefaultFigureSize' after each printing. My solution is a file 'startup.m' in my MATLAB home-directory with the following contents:

set(0,'DefaultFigurePaperType','a4letter',...
      'DefaultFigurePaperOrientation','landscape',...
      'DefaultFigurePaperPosition',[0.5 0.5 11.1 7.7]);

From Chritian Schmid (cs@esr.ruhr-uni-bochum.de): ...I had the same problem and solved it by adding the following statement: set(0,'DefaultFigurePaperType','A4'); to my matlabrc.m file. I found also, that you can retrieve all default setting keywords by entering getpref (undocumented, and no help available) and adding the prefix 'Default' to the keyword in the set(0,...)-statement.

There is a bug in the vwin.sys file in Warp's \os2\mdos directory. The updated file from IBM can be ftp'd from ftp.mathworks.com in /pub/mathworks/bin/os2warp

This is a tricky issue. A discussion including improved code can be found in

    http://www.maths.lth.se/matstat/andersh/histogr

QUICK LITTLE MATLAB HACKS

The first and main trick is "vectorizing", i e avoiding for-loops. Do NOT write things like

    for i = 1:n               % 3 BAD examples  
        z(i) = x(i) * y(i); 
    end

    for i = 1:n                 
        for j = 1:m
            if A(i,j) > B(i,j) 
               C(i,j) = D(i,j);
            else
               C(i,j) = F(i,j);
            end
        end
    end

    for i = 1:n-2               
        Z(i) = 4*X(i+2) + 2*X(i+1) + X(i);
    end

   z = x .* y;                % The GOOD versions

   J = A > B;
   C = D .* J + F .* (~J);
   
   W = [4 2 1];
   Z = filter(W,1,X);
   Z = Z(3:n);

If you really must have for-loops then preallocate memory, it may be a large gain for large vectors, like in the following example.

    x = zeros(10000,1);  % Preallocation of memory!
    x(1) = rand;
    for i = 2:10000
       x(i) = ( 1 - 1.73*x(i-1))^2;
    end 

Another time-saver is using sparse matrices if that is possible. As a last resort one may rewrite the innermost loops into cmex-files.

[15] How can I initialize a this low rank matrix easily?

Here's "Tony's trick", attributed to Tony Booer of Schlumberger:

To initialize a matrix with values "a" in the first row and values "b" in the second row, do the following.

    [a(1,ones(1,m)) ; b(1,ones(1,m))]

with the variant

    [a; b] * ones(1,m)

In Matlab 3.x you have to do something like

    name = 'xyz.mat';
    eval(['save ', name]);
    eval(['load ', name]);

    myfunction qwerty
    myfunction('qwerty')

    sin pi

[17] How can I store the result of `!ls *.dat' in a variable?

    [stat, list] = unix('ls *.dat');

[18] How can I make a variable global from within a function?

You can in Matlab 4. The following hack is from Laura Needles and Mike Kantner . Define the script file `mkglobal.m', containing

    function [] = mkglobal(var)
    % MKGLOBAL      mkglobal(var) - make var a global variable
    if ~exist('mkglobal_var'), mkglobal_1; end;
    mkglobal_var = var; mkglobal_2

Define the script file `mkglobal_1.m' as

    global mkglobal_var

Define the script file `mkglobal_2.m' as

    eval(['global ', mkglobal_var]);

[19] What is a fast way to compute a moving average?

A fast way of computing a moving average of "m" consecutive numbers in the row vector "x" of length "n" is

    z = [0 cumsum(x)];
    y = ( z(m+1:n+1) - z(1:n-m+1) ) / m;

[20] How many times does "a" occur in "x"?

Mauro Jorge Atalla asked if there was a clever vectorized way of counting how many times the components of a matrix are repeated in the matrix and wanted the result to return a matrix with rows of the form

    [number, number_of_times_it_appears_in_the_matrix]

    sortM = sort(M(:));
    uniqueM = [diff(sortM);1] > 0;
    count = [sortM(uniqueM) diff(find([1;uniqueM]))];

    full(sum(sparse(1:length(M(:)),M(:),1)))

Use Tom L. Davis' trick.

    if 0,
       commented out code
    end

[22] What's the area of a polygon?

If "x" and "y" are the coordinate points of a polygon (supposing the last coordinate is the same as the first one), then the shortest and fastest solution seen on the net so far to the problem of computing the area is the following one.

    area = abs(sum(diff(x).*(y(1:nl-1)+y(2:nl)))/2);

[23] How can I set all NaN's to 0?

If a matrix "x" contains NaN's they can be set to 0 by for example Jeffery Faneuff's solution

    x(isnan(x)) = zeros(size(x(isnan(x))));

    x(isnan(x)) = 0;  %ERROR

    x = 1:5
    for i = 1:10, disp(x(ones(1,i))), end

The following works for matrices that are sorted columnwise;

    [xs, i] = sort(x);
    [dummy, j] = sort(i);

    [xs, i] = sort(x);
    j = 1:n;
    j(i) = j;

Use Loren Shure's trick for a n x n matrix "A",

    J = 1:n+1:n^2;
    D = A(J);            % Another form of "D = diag(A);".
    A(J) = zeros(1,n);   % This is not possible to do with "diag".

The question came up how to vectorize the following code.

   % convert from Gray code to binary code
   B = zeros(1,n);
   B(1) = G(1);
   for i=2:n
     B(i) = xor(B(i-1),G(i));
   end

   B = rem(cumsum(G),2);

Here is a tip from Frank Reine (reine@csd.de) for speeding up the distance calculations in for example clustering algorithms. Consider a NxK pattern matrix p with the patterns in its rows and a MxK centroid matrix w with cluster centers in the rows. Our goal is to calculate the NxM distance matrix d. Now, instead of using something like

for i = 1:M
   d(:,i) = sum((p-ones(N,1)*w(i,:))'.^2)'
end

s2 = sum(p'.^2)';
w2 = sum(w'.^2);
d = s2(:,ones(1,M)) - 2*p*w'+ w2(ones(N,1),:);