how to split a large matrix into smaller matrices and assign random values

Question

Andrew Poissant 2017-2-27

0
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https://ww2.mathworks.cn/matlabcentral/answers/327031-how-to-split-a-large-matrix-into-smaller-matrices-and-assign-random-values

评论： Andrew Poissant 2017-2-27

I have a 180x180 matrix of 0's and I was to assign different range of random integers to each 45x45 set in the matrix. I have show the example output that I want for a much smaller matrix (10x10) that breaks it up into 5x5 matrices of different random values below. Any easy way to do this that doesn't involve a million for loops? I just want to expand this code to an N = zeros(180,180) type deal with 45x45 subparts.

N = zeros(10,10);
for i = 1:5
    for j = 1:5
        N(i,j) = randi([1,10]);
    end
end
for i = 1:5
    for j = 6:10 
        N(i,j) = randi([15,100])
    end
end
for i = 6:10
    for j = 6:10 
        N(i,j) = randi([1,17])
    end
end
for i = 6:10
    for j = 1:5 
        N(i,j) = randi([100,250])
    end
end
N

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Answer 1

Walter Roberson 2017-2-27

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https://ww2.mathworks.cn/matlabcentral/answers/327031-how-to-split-a-large-matrix-into-smaller-matrices-and-assign-random-values#answer_256409

在 MATLAB Online 中打开

low_vals = [1 15 1 100;
            8 -4 17 3;
            1 2 9 15;
            0 -8 3 72];
high_vals = [10 100 17 250;
             14 11 84 9;
             33 11 99 222;
             4 -3 88 105];
N = cell2mat( arrayfun(@(L, H) randi([L, H], 45, 45), low_vals, high_vals, 'Uniform', 0) );

The above would create 4 x 4 of 45 x 45 subblocks.

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Walter Roberson 2017-2-27

Did you run the above code? It creates a 180 x 180 matrix in which each 45 x 45 (non-overlapped) sub-block is based on randi() between the corresponding low value and high value. For example, the third sub-block over on the second row of sub-blocks would be based on randi([17, 84], 45, 45) in the above demonstration code.

Andrew Poissant 2017-2-27