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How can I store a matrix of varying size in each iteration of a for loop?

Asked by Mathushan Sabanayagam on 2 Aug 2019
Latest activity Commented on by madhan ravi
on 2 Aug 2019
Hi,
I have a function that gives an output of a single column, T, and also a matrix Y. The number of columns of Y remains constant but the number of rows changes depending on the input parameter. The number of rows of T also changes depending on the input parameter.
for rho = 500:100:1000
[T Y]= myFunction(rho)
end
I am varying the parameter rho from 500 to 1000, however want to store each iteration in a separate matrix, as I wish to compare the outputs at different rho values. Currently, although all matrix outputs appear in the command window, I cannot store each iteration for further use, only the last iteration at rho=1000 is accessible. I was wondering how this would be possible? Thank you very much for any help as I am a beginner to Matlab.
An example of the output in the command window for one value of rho inputted:
Screenshot 2019-08-02 at 14.43.19.png

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1 Answer

Answer by Jos (10584)
on 2 Aug 2019
 Accepted Answer

Since T and Y are related for a specific value of rho, a struct array is useful here.
rho_range = 500:100:1000 ;
for k = 1:numel(rho_range)
rho = rho_range(k) ;
[data(k).T data(k).Y]= myFunction(rho) ;
end
You might want to pre-allocate the struct array to speed things up. One easy way to do this is to reverse the loop:
for k = numel(rho_range):-1:1

  3 Comments

My pleasure. Unfortunately, user madhan ravi deleted his answer, as cell arrays are a good option too.
[T{k}, Y{k}] = myFunction(rho) ;
Note: Preallocating variables is important.

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