dynamically save a matrix to a structure

I have a loop that evaluates a matrix X for each scenario. The size of this matrix X changes at each iteration, and the values too. I would like to make a structure X.1, X.2 etc to X.(n), and save the result X. When I do eval(['[Z.SET'num2str(J) ']= (Xtmp);']); X.1 gets overwritten by X.2, what I mean is that at first I have X.1 with the desired X matrix, but at the next loop, X.1 is no longer there and there is X.2 (with the corresponding X matrix). How can I “save” the X.1 so that it doesn’t get overwritten?

Answer 1

[Stephen23]

Do NOT use eval for trivial code like this.

That approach is slow, complex, inefficient, and not recommended. Rather than messing around with fieldnames like that, the simple and efficient MATLAB solution would be to just use indexing into a cell array or structure array, e.g.:

C = cell(1,N);
for k = 1:N
    ...
    C{k} = Xtmp;
end

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

Or if you really want to use a structure:

C = struct('X',cell(1,N));
for k = 1:N
    ...
    C(k).X = Xtmp;
end

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html