How would I keep adding matrices to an array using a for loop?

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tash7827 2015-8-3

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回答： the cyclist 2015-8-3

I have managed to concatenate two matrices, but I would like to have ten total - what is wrong with my code?

A=zeros(60,96);
for exp = 1:10;
        n=1;
        while n<61
        pop=randperm(96,60);
        m = pop(n);
        A(n,m)=1;
start=A;
array=cat(3,start,A);
        n=n+1;
        end
end

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Sean de Wolski 2015-8-3

Perhaps this will help clarify for us: What is your end goal, i.e. what do you want the end array to look like (forget the steps for getting there right now)?

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Answer 1

the cyclist 2015-8-3

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It is not perfectly clear to me what you are trying to do, but I think the core of your problem is that in the line

array=cat(3,start,A);

You simply append start and A, over and over again. This does not "grow" the array. It just keeps making a (60,96,2) array.

It seems that what you actually want to do is to append to array, and then keep appending to array. So, maybe you want this line to be something like

array=cat(3,start,array);

Does that seem right?

Now, that being said, growing an array like this is a bad idea, from a memory usage point of view. Better practice (with potentially huge execution time benefit) would be to preallocate array

array = zeros(60,96,10)

and then fill in each "slice" as you go.

But it is OK start by fixing your own code, before you worry about optimizing.