Submatrix sum (but just on a section)

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Hugo Campos Romero 2021-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/850590-submatrix-sum-but-just-on-a-section

编辑： Matt J 2021-6-8

I have a square 4915x4915 matrix (189 countries, 26 sectors for each country and a row and column adjustment). Each country-sector group can be understood as a submatrix. I need to agregate some countries but maintaining the sectoral structure. For example, I need to sum up the elements between 4187:4914 rows and get a 26*4915 submatrix in that space and then repeat the procces for the colums, summing up from column 4187 to column 4914, getting a 4915*26 submatrix in that space, without chainging anythig else in the matrix.

Thanks in advance.

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KSSV 2021-6-8

Play with indices. Read about MATLAB array indexing.

Hugo Campos Romero 2021-6-8

Thank you. I am actually able to do it, but in a rather "rudimentary" way. I am convinced that there are faster methods than mine, which is to extract the section I am interested in modifying, make the changes, and then reinsert it.

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Answer 1

Matt J 2021-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/850590-submatrix-sum-but-just-on-a-section#answer_719580

编辑：Matt J 2021-6-8

You can use sepblockfun (Download)

A=rand(4914);
B1=sepblockfun(A,[189,1],'sum'); %the results
B2=sepblockfun(A,[1,189],'sum');
whos B*
  Name         Size                Bytes  Class     Attributes

  B1          26x4914            1022112  double              
  B2        4914x26              1022112  double              