INTEGER; OPTIONAL; scalar; INTENT(IN).
Returns a uniform quasi-random number between 0 and 1.
If Flag is 0, the next number in sequence is returned; if
Flag is 1, the generator is restarted by calling
if Flag has any other value, it is used as a new seed with
See SRand Intrinsic.
Note: As typically implemented (by the routine of the same name in the C library), this random number generator is a very poor one, though the BSD and GNU libraries provide a much better implementation than the `traditional' one. On a different system you almost certainly want to use something better.