Here a simple example: You want to run 100x times of this function, y=2i, where i is integer values (0 until 100) and you want to save each y into a single matrix (named as y1), you can write as follow:
for i=1:100 % 100 times of loops
y=2*i % our function
y1(i,:)=y % each y will save on a single column in the matrix end
I found a good tip from the matlab community to find out the built-in function in Matlab. You can edit and change it. The tip as follows:
% You can use the [which] command to find the path name to the
% built-in function in question, i.e. -
% then point Matlab to that folder on your computer so that
% the fft.m file is in your "current folder" window. Then use
% the  command to edit the function, i.e. -
% The code for the fft function will appear in the editor window.
% Often it is useful to make small changes to the built-in code
% then comment out the changes as soon as you're done so that
% Matlab will continue to function as designed.