# RANDOM Subroutine

Portability Subroutine: Returns a pseudorandom number greater than or equal to zero and less than one from the uniform distribution.

## Module

USE IFPORT

CALL RANDOM (ranval)

ranval | (Output) REAL(4). Pseudorandom number, 0 ranval< 1, from the uniform distribution.

A given seed always produces the same sequence of values from RANDOM.

If SEED is not called before the first call to RANDOM, RANDOM begins with a seed value of one. If a program must have a different pseudorandom sequence each time it runs, pass the constant RND$TIMESEED (defined in `IFCORE.F90`) to SEED before the first call to RANDOM.

The portability routines DRAND, DRANDM, IRAND, IRANDM, RAN, RAND, and the RANDOM portability function and subroutine use the same algorithms and thus return the same answers. They are all compatible and can be used interchangeably. The algorithm used is a "Prime Modulus M Multiplicative Linear Congruential Generator," a modified version of the random number generator by Park and Miller in "Random Number Generators: Good Ones Are Hard to Find," CACM, October 1988, Vol. 31, No. 10.

## Example

     USE IFPORT
     REAL(4) ran

     CALL SEED(1995)
     CALL RANDOM(ran)

The following example shows how to use both the RANDOM subroutine and the RANDOM function:

    use ifport
    real(4) ranval
    ! from libifcore.lib
    call seed(1995)     ! initialize
    ! also from for_m_irand.c in libfor
    call random(ranval) ! get next random number

    print *,ranval
    ! from libifport.lib
    ranval = random(1)  ! initialize
    ! same
    ranval = random(0)  ! get next random number

    print *,ranval
    end

Parent topic: Q to R

## See Also

RANDOM_NUMBER
SEED
DRAND and DRANDM
IRAND and IRANDM
RAN
RAND