N-point circular convolution

% C = CIRCONV(A,B,N) performs the N-point circular convolution
% of vectors A and B. C is returned as a row vector. A and B
% must be vectors, but may be of different lengths. N must be
% a positive, non-zero integer. The results of CIRCONV will
% match that of CONV if N>=( length(A) + length(B) - 1). This
% is also the alias-free criterion for the circular convolution.