summations and selections of the columns of a matrix

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ELISABETTA BILLOTTA
ELISABETTA BILLOTTA 2021-10-28
评论： ELISABETTA BILLOTTA 2021-10-28
I have a matrix of this type
10 15 37 16
6 4 3 5
15 66 85 96
17 89 15 82
58 66 78 100
I have to understand how to do two procedures:
1) calculate the sums of the subsequent column numbers, for example :
the first line remains the same 10 15 37 16
the second line must be 6+15+17+58 4+66+89+66 3+85+15+78 5+96+82+100
the third line must be 5+17+58 66+89+66 85+12+78 6+82+100
and so on ... can someone tell me how it can be done?
2) in the script then I have to consider the last one formed by as the first column
16
5
96
85
100
as the second column
37
3
85
15
78
and so on .. how do you select any column of the matrix you can use?
  2 个评论
Johnny Himbele
Johnny Himbele 2021-10-28
Hi Elisabetta,
A cumsum function can achieve what you're trying to do. For more information, please refer to this link.
For example,
A = magic(5);
B = [A(1,:); cumsum(A(2:end,:),'reverse')];
If you want to select any specific columns, please replace a colon to any column indices.
% First column
C = [A(1,1); cumsum(A(2:end,1),'reverse')];
% Second and third columns
D = [A(1,2:3); cumsum(A(2:end,2:3),'reverse')];
Johnny

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David Hill
David Hill 2021-10-28
newMatrix=[yourMatrix(1,:);flipud(cumsum(flipud(yourMatrix(2:end,:))))];
  1 个评论
ELISABETTA BILLOTTA
ELISABETTA BILLOTTA 2021-10-28
ok thanks ... I understand that is the answer to point 1 and it works .. thanks a lot .. and for point two?

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