pmatrix: Parallelize columnwise computations on a matrix using forking
(generalizes function 'pvec' from package 'parallel')
Description
parellelizes the execution of a function on matrix elements
by splitting the matrix by columns and submitting each part to one core.
The function must take a matrix argument, with computations depending on
row entries. It creates a matrix with same number of columns as on input,
but possibly different number of rows.