# How to add columns of accumulated sum in a matrix

2 vues (au cours des 30 derniers jours)
Philippe Corner le 23 Jan 2018
Commenté : Star Strider le 24 Jan 2018
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
1 101 1 1 1
2 102 3 3 3
3 103 5 6 6
4 104 7 9 10
5 105 9 12 14
6 106 11 15 18
7 107 13 18 22
8 108 15 21 26
9 109 17 24 30
10 110 19 27 34
11 111 21 30 38
12 112 13 33 42
. . . . .
. . . . .
. . . . .
etc etc etc etc etc ... etc -> until 20
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Star Strider le 23 Jan 2018
Note: this is not homework. It’s meteorology or climatology research.
Philippe Corner le 23 Jan 2018
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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### Réponse acceptée

Star Strider le 24 Jan 2018
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
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Philippe Corner le 24 Jan 2018
crack.
Star Strider le 24 Jan 2018
Thank you!

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### Plus de réponses (1)

Image Analyst le 23 Jan 2018
Sounds like homework. See if you can figure out how to use the cumsum() function to do it. Let us know if you really can't figure it out.
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Philippe Corner le 23 Jan 2018
I already did with cumsum(), but im trying to figure it out with more columns and im trying to automatize the code for that.

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