Introduction - If you have any usage issues, please Google them yourself
Discrete cosine transform is equivalent to a length of about twice its discrete Fourier transform, the discrete Fourier transform is on a solid even functions (because of a real even function of Fourier transform, is still a real even functions). The Discrete Fourier Transform is a real dual function of (as a real dual function of the Fourier Transform is still a real dual function). This procedure is to achieve the transformation