离散余弦变换 (2i+1)mt (,1)=cos 2T 2(2i+1)kx ik COS k=12..N N k=0 实数运算简单些。离散余弦变换    ( , ) cos ( ) , cos ( ) , , ... , i t i t T a N i k N k N N k ik = + = + = − = = 2 1 2 2 2 1 1 2 1 1 0 实数运算简单些