> what is the error with my code
The error is,
N = 4;
x = [ 3 4 5 6 ];
for k = 0 : N-1
for n=0:N-1
sum = sum + x.*(exp(-1*1i*2*pi*k.*n/N));
% ^^^ ERROR
end
end
stem(sum)
What is causing the error (the question you intended to ask)?
sum() is a very commonly used Matlab function.
You're using it as a variable name but Matlab doesn't know it's a variable name because you haven't declared it as a variable by assiging a value to it.
Solution
Don't use sum as a variable name.
