function [v,w]=hw2_1_13(A)

% input: A is a 4x5 matrix (actually the size doesn't matter) 
% output: v and w are row vectors containing the colmun sums of A 

% get the size of A and initialize v
[m,n]=size(A);
v=zeros(1,n);

% usually use i for rows, j for columns (r and c are good loop variables to)
for j=1:n
    for i=1:m
        v(j)=v(j)+A(i,j);
    end
end
v

% now use the sum function, call the 1x5 row vector w this time
w=sum(A)