Nested Loop, Can someone help me to understand this code?

Inspect the (basic) functionality of the cumsum function, then implement your own (mycumsum). Only implement the functionality of the first 3 documentation lines, not all the special cases!

function Y = mycumsum(X) 
%MYCUMSUM cumulative sum of elements. 
Y = X;
[r,c] = size(Y); 
for ii = 2:r 
for jj = 1:c 
Y(ii,jj) = Y(ii,jj) + Y(ii-1,jj); 
end 
end 
end

Can someone help me to understand this code?

[Stephen23]

http://web.archive.org/web/20210203144546/https://www.mathworks.com/matlabcentral/answers/734977-nested-loop-can-someone-help-me-to-understand-this-code

Answer 1

[David Hill]

function Y = mycumsum(X) 
Y = X;
[r,c] = size(Y); %determine size of maxtrix
for ii = 2:r %1st row will stay constant, start at 2nd row
    for jj = 1:c %go through all columns
        Y(ii,jj) = Y(ii,jj) + Y(ii-1,jj); %first step Y(2,1)=Y(2,1)+Y(1,1) then Y(3,1)=Y(3,1)+Y(2,1),...  this is the cumulative add of column
    end 
end 
end

[Kaouthar Bouyaouzan]

Thank you very much.