How to add columns of accumulated sum in a matrix

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Philippe Corner 2018-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/378621-how-to-add-columns-of-accumulated-sum-in-a-matrix

评论： Star Strider 2018-1-24

If a have this matrix:

A=[1:1:100]
B=[101:1:200]
M=[A(:), B(:)]

I need to add 20 columns to M which contain the summation of A values like:

C = summation of the row |i| + the row |i-1|,
D = summation of the row |i| + the row |i-1|+|i-2|,
E = summation of of the row |i| + the row |i-1|+|i-2|+|i-3|,.. etc

and M=[A(:), B(:), C(:), D(:), E(:) ...etc]

For example: it would be something like:

A  B  C  D  E.. etc -> until 20
101  1  1  1
102  3  3  3
103  5  6  6
104  7  9  10
105  9  12  14
106  11  15  18
107  13  18  22
108  15  21  26
109  17  24  30
110  19  27  34
111  21  30  38
112  13  33  42
.  .  .  .  .
.  .  .  .  .
.  .  .  .  .
etc  etc  etc  etc  etc ... etc -> until 20

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Star Strider 2018-1-23

Note: this is not homework. It’s meteorology or climatology research.

Philippe Corner 2018-1-23

Yep, im trying to analyze some climate data. But for my bachelor thesis. I already did a cumsum, but there are too many columns, so im looking for a more automatic way to do it..

Thanks in advance Mr Star.

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Answer 1

Star Strider 2018-1-24

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https://ww2.mathworks.cn/matlabcentral/answers/378621-how-to-add-columns-of-accumulated-sum-in-a-matrix#answer_301456

在 MATLAB Online 中打开

This seems to work for ‘C’, ‘D’ ... ‘T’.

This construction seems the only way to form your matrix (that I call ‘Ar’ here).

A = (1:100)';
Ar(1,:) = ones(1, 20);
for k1 = 2:numel(A)
    if k1 <= 20
        v1 = cumsum(A(k1:-1:max(1,k1-19)));
        Ar(k1,:) = [v1(2:end)' v1(end)*ones(1, 21-k1)];
    else
        v1 = cumsum(A(k1:-1:1));
        Ar(k1,:) = v1(2:21)';
    end
end