MATLAB does not need a return statement to return a value. To return a value you simply need to list it as an output argument of the function:
function [output1,output2,...] = fun_name(input1,input2,...)
You have specified an output argument rad, but then have totally ignored this inside your code an never allocated any value to it. You should try something like this:
function rad = Radial(n,m);
rad = ... whatever rad is;
end
Of course this is explained quite clearly in the introductory tutorials:
Read the documentation. It tells you how MATLAB works.
If you want to store all of the values of rad in a loop then you can use indexing.
