function c = dstmtx(n)
%DSTMTX Discrete sine transform matrix.
% D = DSTMTX(N) returns the N-by-N DST transform matrix. D*A is the DST
% of the columns of A and D'*A is the inverse DST of the columns of A
% (when A is N-by-N).
% If A is square, the two-dimensional DST of A can be computed as D*A*D'.
% This computation is sometimes faster than using DSTN, especially if you
% are computing large number of small DST's, because D needs to be
% determined only once.
% Class Support
% N is an integer scalar of class double. D is returned as a matrix of
% class double.
% A = im2double(imread('rice.png'));
% D = dstmtx(size(A,1));
% dst = D*A*D';
% figure, imshow(dst)
% See also DSTN, IDSTN, DCTMTX
% -- Damien Garcia -- 2009/11
% -- Adapted from DCTMTX --
% website: <a
% I/O Spec
% N - input must be double
% D - output DCT transform matrix is double
[cc,rr] = meshgrid(0:n-1);
c = sqrt(2 / n) * sin(pi * (2*cc + 1) .* (rr + 1) / (2 * n));
c(n,:) = c(n,:) / sqrt(2);