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, i.e.

%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).

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This approach looks more robust to me.