Intrinsic Subroutine: Returns one pseudorandom number or an array of such numbers.
Syntax
CALL RANDOM_NUMBER (harvest)
harvest
(Output) Must be of type real. It can be a scalar or an array variable. It is set to contain pseudorandom numbers from the uniform distribution within the range 0 x < 1.
The seed for the pseudorandom number generator used by RANDOM_NUMBER can be set or queried with RANDOM_SEED. If RANDOM_SEED is not used, the processor sets the seed for RANDOM_NUMBER to a processor-dependent value.
The RANDOM_NUMBER generator uses two separate congruential generators together to produce a period of approximately 10**18, and produces real pseudorandom results with a uniform distribution in (0,1). It accepts two integer seeds, the first of which is reduced to the range [1, 2147483562]. The second seed is reduced to the range [1, 2147483398]. This means that the generator effectively uses two 31-bit seeds.
For more information on the algorithm, see the following:
See Also
RANDOM_SEED, RANDOM, SEED, DRAND and DRANDM, IRAND and IRANDM, RAN, RAND and RANDOM
Examples
Consider the following:
REAL Y, Z (5, 5)
! Initialize Y with a pseudorandom number
CALL RANDOM_NUMBER (HARVEST = Y)
CALL RANDOM_NUMBER (Z)
Y and Z contain uniformly distributed random numbers.
The following shows another example:
REAL x, array1 (5, 5)
CALL RANDOM_SEED()
CALL RANDOM_NUMBER(x)
CALL RANDOM_NUMBER(array1)
Consider also the following:
program testrand
intrinsic random_seed, random_number
integer size, seed(2), gseed(2), hiseed(2), zseed(2)
real harvest(10)
data seed /123456789, 987654321/
data hiseed /-1, -1/
data zseed /0, 0/
call random_seed(SIZE=size)
print *,"size ",size
call random_seed(PUT=hiseed(1:size))
call random_seed(GET=gseed(1:size))
print *,"hiseed gseed", hiseed, gseed
call random_seed(PUT=zseed(1:size))
call random_seed(GET=gseed(1:size))
print *,"zseed gseed ", zseed, gseed
call random_seed(PUT=seed(1:size))
call random_seed(GET=gseed(1:size))
call random_number(HARVEST=harvest)
print *, "seed gseed ", seed, gseed
print *, "harvest"
print *, harvest
call random_seed(GET=gseed(1:size))
print *,"gseed after harvest ", gseed
end program testrand