dct(X[, type=2])
Replaces the columns of a dense real matrix with their discrete cosine transforms. The second argument, an integer between 1 and 4, denotes the type of transform (DCT-I, DCT-II, DCT-III, DCT-IV). The DCT-I transform requires that the row dimension of X is at least 2. These transforms are defined as follows (for a matrix with n rows).
idct(X[, type=2])
Replaces the columns of a dense real matrix with the inverses of the discrete cosine transforms defined above.