Pre-locating an array

Question

Susan 2019-4-10

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评论： Susan 2019-4-10

采纳的回答： James Tursa

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Hi MATLAB guys,

I got stuck at some point and really appreciate your help.

Do you know how can I pre-locate the value of X in the following code? X is a matrix and for each i and j its dimentions will change. For example for given i and j, X has a dimention of Ri * Tj.

N = [1 2 3 4 5 6 7 8 9 10];
M = [11 22 33];
X === zeros  %%%%pre-locating here
for k = 1 : 10
    for m = 1 : N(k)
       for i = 1 : 3;
         for j = 1: M(i)
              X(:,:, j,i,m,k) = sth;
        end
      end
   end
end

Thanks in advance

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Rik 2019-4-10

Do you know the size of sth in advance?

Susan 2019-4-10

编辑：Susan 2019-4-10

Thanks for your reply. It depends on the i and j and for different i and j the size of this matrix is different. And, yes, I know the sizes in advance.

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Answer 1

James Tursa 2019-4-10

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https://ww2.mathworks.cn/matlabcentral/answers/455584-pre-locating-an-array#answer_370046

编辑：James Tursa 2019-4-10

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Numeric arrays must be rectangular. You cannot have different dimensions for different slices. To get that behavior you would need to use something like a cell array to store your different sized variables. E.g.,

X{j,i,m,k} = sth;

But, even though the contents of the cell array elements do not all have to be the same size, the cell array itself must be rectangular. You could still use it in your above scheme as long as it was OK to have a bunch of empty cells in the spots you were not using.

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Rik 2019-4-10

编辑：Rik 2019-4-10

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You can use the code James suggested, and you can do it like this:

N = [1 2 3 4 5 6 7 8 9 10];
M = [11 22 33];
X=cell(max(M(:)),numel(M),max(N(:)),numel(N));
for k = 1 : numel(N)
    for m = 1 : N(k)
       for i = 1 : numel(M)
         for j = 1: M(i)
             X{j,i,m,k} = sth;
         end
       end
    end
end