How can I change elements in a matrix all at once??

How can I change each element in a matrix so that each new element is for example itself + the element next to it?

Answer 1

[Jan]

This seems to be a job for cumsum. A small example would clear the details.

[EDITED] After your comment: NO, not cumsum. See Kelly's answer.

[Ken Mills]

For example if I have mtx = [1 2 3; 4 5 6; 7 8 9] then the new element would be [3 5 3; 9 11 6; 15 17 9] Something like that.

Answer 2

[Kelly Kearney]

new = mtx + [mtx(:,2:end) zeros(size(mtx,1),1)]