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frandom(-F)

Generates a random floating-point number F in the range <0, 1>.
F
Floating-point number or variable.

Description

frandom/1 unifies F with a random floating-point number between 0 and 1. The code is taken from random2.c by John Burton, available from the net. Part of original comment:

 *
 * PMMMLCG - Prime Modulus M Multiplicative Linear Congruential Generator   *
 *  Modified version of the Random number generator proposed by             *
 *  Park & Miller in "Random Number Generators: Good Ones Are Hard to Find" *
 *  CACM October 1988, Vol 31, No. 10                                       *
 *   - Modifications proposed by Park to provide better statistical         *
 *     properties (i.e. more "random" - less correlation between sets of    *
 *     generated numbers                                                    *
 *   - generator is of the form                                             *
 *         x = ( x * A) % M                                                 *
 *   - Choice of A & M can radically modify the properties of the generator *
 *     the current values were chosen after followup work to the original   *
 *     paper mentioned above.                                               *
 *   - The generator has a period of 0x3fffffff with numbers generated in   *
 *     the range of 0 < x < M                                               *
 *   - The generator can run on any machine with a 32-bit integer, without  *
 *     overflow.                                                            *

Modes and Determinism

Exceptions

(5) type error
F is instantiated, but not to a floating-point number.

Examples

Success:
      ?- frandom(F1), frandom(F2).
      F1 = 0.900086582
      F2 = 0.0795856342
      yes.

      ?- seed(1), frandom(F).
      F = 2.2477936e-05
      yes.
      ?- seed(1), frandom(F).
      F = 2.2477936e-05
      yes.

Fail:
      frandom(123.45).

Error:
      frandom(1234).          (Error 5).

See Also

seed / 1, random / 1