How do I replace a single value within a .m matlab file?

Question

I have a .m file that contains a struct with some matrices:

%mymatfile.m

function [mymatrix,anothermatrix] = mymatfile;

mymatrix = [
1   2   0.0010  0.0010  0.0000  2.0000  2.0000  2.0000  1   0   1
2   3   2.0014  0.0007  0.0000  0.5000  0.5000  0.5000  0   0   1
3   4   0.0301  0.0001  4.0000  0.5000  0.5000  0.5000  1.16    0   1
4   5   0.0791  0.0450  0.0000  0.5000  0.5000  0.5000  0   0   1
5   6   1.0482  0.0233  0.0000  0.5000  0.5000  0.5000  0   0   1
5   7   7.5130  0.0467  0.0000  0.5000  0.5000  0.5000  0*  0   1
7   8   9.0161  0.0008  0.0000  0.5000  0.5000  0.5000  0   0   1
7   9   0.9070  0.2310  0.0000  0.5000  0.5000  0.5000  0   0   1
];

anothermatrix = [
2   0   0   3   0   10  0               
9   0   0   3   0   10  0   
%];

How do I change just the starred value (mymatrix(3,9)) and save the file, whilst retaining its structure/formatting? I need to perform the update from another matlab script.

Answer 1

You could save the entries of mymatrix in a text file, say mymatrix_text .

Then you make your function read that text file, ie

%mymatfile.m

  [mymatrix,anothermatrix]   = function get_my_matrices()

  fid = fopen(mymatrix_text);

  mymatrix = fscanf(fid, '%g ');

  fclose(fid);

  % anothermatrix =  %% you can do the same above..

  end

Now if you need to modify your matrix, you should just modify the text file -which is way easier and doesn't involve changing your .m file.

(For instance you may create another function to read mymatrix_text and change the desired values).

---

This approach looks more robust to me.

Answer 2

Substitute a number in for the old one. The fields seem to be tab delimited.

Answer 3

Here's how I did it in the end (note that S is the value used to update the file):

fid = fopen('mymatfile.m')  % open settings file
fseek(fid,1196,-1)      % set read position
Line = fgets(fid)       % read in line
Refline = Line          % set reference for search and replace later
Line(47:51) = S         % update specific characters in the line with new setting
fclose(fid)             % close file
wholefile = fileread('test.m')                  % read in entire file
newfiledata = strrep(wholefile,Refline,Line)    % replace line
fid2 = fopen('mymatfile.m','w')                 % open file to write
fprintf(fid2,'%s',newfiledata)                  % save to file
fclose(fid2)

With help from here: [http://www.mathworks.com/matlabcentral/answers/7066].