Comments on "DCT algorithms for composite sequence lengths"

In the above paper, Bi and Yu 1 proposed radix algorithms for the type II and III discrete cosine transforms (DCT) of composite sequence lengths. Some corrections in this interesting paper are required, and certain factors of 2 should be introduced or removed. They are derived from (3) to (8) in the paper by utilizing trigonometric identities. a) In equations (9) and (10) of the paper, the in the denominator of the last term should be replaced by . This factor of 2 can be cancelled with the 2 in the numerator of (9).