title: MATLAB dct2/idct2 vs. dctmtx
body: <p>There are two alternative methods to compute DCT and its inverse in MATLAB. One is <code>dct2</code>/<code>idct2</code> and the other is the transformation matrix computed by <code>dctmtx</code>. Why is there an alternative way based on matrix multiplications making use of <code>dctmtx</code>?</p>