Section 11,74: RAN

 RAN (seed)

 A function that is a general random number generator of the
 multiplicative congruential type.  This function returns a
 different REAL*4 number between 0.0 (inclusive) and 1.0 (exclusive)
 each time it is invoked.  The argument must be an INTEGER*4
 variable or array element.

 For best results, you should initialize the argument to a large,
 odd value before invoking RAN the first time.  To generate
 different sets of random values, initialize the seed to a different
 value on each run.  Do not modify the seed during a run.