How can I turn a matrix into several submatrices and add up certain submarices?

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Paul Wolfram
Paul Wolfram 2017-9-3
编辑： Paul Wolfram 2017-9-3
Hi community,
I am wondering how to turn a large matrix (9800x9800) into 49x49 submatrices (each with 200x200 cells). Following that, I want to do the following operations:
  1. sum up all matrices on the diagonale
  2. sum up all matrices in the lower triangle
  3. sum up all matrices in the upper triangle
I have been succesful with the first item using the following code:
for i = 1 : meta.NCOUNTRIES;
i
Z_all{i} = Z((i - 1) * meta.NSECTORS + 1 : i * meta.NSECTORS, (i - 1) * meta.NSECTORS + 1 : i * meta.NSECTORS);
end
Z_RoW = zeros(meta.NSECTORS);
for i = 1 : meta.NCOUNTRIES;
i
Z_RoW = Z_RoW + Z_all{i};
end
where
  • meta.NCOUNTRIES = 49
  • meta.NSECTORS = 200
  • meta.Zdim = 9800
I think the above code is not ideal, i.e. it could be done w/o having to use a loop. Also, I have troubles with finding and summing up the elements in the lower/upper triangle.
Thank you!

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回答（1 个）

Image Analyst
Image Analyst 2017-9-3
  1 个评论
Paul Wolfram
Paul Wolfram 2017-9-3
编辑：Paul Wolfram 2017-9-3
Hi Image Analyst,
this is nice for splitting up the matrix. I am still unsure though how to add up certain matrices, e.g. only the matrices in the lower or upper triangle (as shown in yellow shades / green shades in the picture below).
Thank you!

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