Replaces the columns of a dense real matrix with their discrete
sine transforms. The second argument, an integer between 1 and 4,
denotes the type of transform (DST-I, DST-II, DST-III, DST-IV).
These transforms are defined as follows
(for a matrix with n rows).
idst(
X[, type=1])
Replaces the columns of a dense real matrix with the inverses
of the discrete sine transforms defined above.