summations and selections of the columns of a matrix

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?

[Johnny Himbele]

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

[ELISABETTA BILLOTTA]

perfect thank you very much!!!!

Answer 1

[David Hill]

newMatrix=[yourMatrix(1,:);flipud(cumsum(flipud(yourMatrix(2:end,:))))];

[ELISABETTA BILLOTTA]

ok thanks ... I understand that is the answer to point 1 and it works .. thanks a lot .. and for point two?