create a function to...

Create a function *.m file that accepts a 2-dimensional array as a function input and has two function outputs. This function will use a nested loop to create one column vector that contains the sum of all the positive values in each row and another column vector that contains sum of all the negative numbers of each row. These two column vectors should be returned (sent back) to the function call.

[Mike]

my attempt:

function [ positive, negative ] = Untitled2( x )
%UNTITLED2 Summary of this function goes here
%   Detailed explanation goes here

positive=0;
negative=0;
for k=1:length(x)
    for j=1:length(x)
        if x(k,j)>0
            positive=positive+x(k,j)
        end
        if x(k,j)<0
            negative=negative+x(k,j)
        end
    end
end
positive=positive
negative-negative

end

Answer 1

[Cedric]

It's not bad actually. The lines

 positive=positive
 negative-negative

are useless, and you want to create vectors of sums, not scalars. So one mistake is that you don't index variables positive and negative with the row index. To make it more efficient, you could even prealloc these variables: change

 positive=0;
 negative=0;

for

 positive = zeros(size(x, 1));
 negative = zeros(size(x, 1));

Another mistake is that k and j should go from 1 to the number of rows and columns of x. You can obtain them using function SIZE.

Answer 2

[Matt J]

Make "positive" and "negative" into vectors and index them appropriately, e.g.,

 positive(k)=positive(k)+x(k,j)