x is a matrix with arbitrary number of rows but whose columns
are equal to the number of bins that the stochastic matrix prob parameterizes
a distribution over. Each row of x gives a distribution of counts over bins
and is resampled according to prob. It is conceptually similar to
"stochastically" distributing the matrix as x %*% prob, which gives the
expectation.
sample_stochastic_matrix(x, prob)a matrix whose dimensions equal the original x
a matrix
a matrix, it must have number of columns equal to the number of columns of x and rows that sum
to one