dctmtx [y]=dctmtx(n) n: Real scalar integer greater than or equal to 1 This is an Octave function dctmtx(n) returns a Discrete cosine transform matrix of order n-by-n. It is useful for jpeg image compression. D*A is the DCT of the columns of A and D'*A is the inverse DCT of the columns of A (when A is n-by-n).