I have written a short monte carlo integration algorithm to calculate an integral in Fortran 90. I once compared the result obtained by solving the integral with respect to
The particular random number generator used depends on the compiler. Perhaps documented, perhaps not. Perhaps subject to change. For high quality work, I would use library / source code from elsewhere. A webpage with Fortran implementations of the Mersenne Twister: http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/VERSIONS/FORTRAN/fortran.html. I have used http://theo.phys.sci.hiroshima-u.ac.jp/~ishikawa/PRNG/mt_stream_en.html and verified against the original implementation. This version is useful for multi-threaded programs.