Visible to Intel only — GUID: GUID-A687BB5C-A35D-4F4F-9400-C903D8236AB7
Visible to Intel only — GUID: GUID-A687BB5C-A35D-4F4F-9400-C903D8236AB7
RANDOM_NUMBER
Intrinsic Subroutine: Returns one pseudorandom number or an array of such numbers.
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.
The RANDOM_NUMBER generator does not produce subnormal numbers.
For more information on the algorithm, see the following:
Communications of the ACM vol 31 num 6 June 1988, titled: Efficient and Portable Combined Random Number Generators by Pierre L'ecuyer.
Springer-Verlag New York, N. Y. 2nd ed. 1987, titled: A Guide to Simulation by Bratley, P., Fox, B. L., and Schrage, L. E.
This routine is thread safe.
Example
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)
The following shows another example:
program testrand
intrinsic random_seed, random_number
integer size
integer, allocatable :: seed(:), gseed(:), hiseed(:), zseed(:)
real harvest(10)
call random_seed(SIZE=size)
print *,"size ",size
allocate(seed(size),gseed(size),hiseed(size),zseed(size))
hiseed = -1
zseed = 0
seed = 123456789
seed(size) = 987654321
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