When you call a function that has outputs, you need to store the outputs into variables if you want to use them. A syntax such as
function [A, B] = testfunction
does not result in A and B being stored in the caller: it tells MATLAB to use A and B to "stand in" for whatever output variables that the user is assigning the values to.
We recommend that you do not use "sum" as the name of a variable: you will almost certainly eventually try to use sum() as a function in the same routine that you used sum as a variable.
