1module randomNumber_mod
2 ! MODULE randomNumber_mod (prefix='rng' category='8. Low-level utilities and constants')
3 !
4 !:Purpose: A Gaussian random number generator (RNG) module. The actual calculation
5 ! is performed by functions in an external library.
6 !
7 use ISO_C_BINDING
8 implicit none
9
10 include 'randomfunctions.inc'
11
12 save
13 private
14
15 ! public procedures
16 public :: rng_setup, rng_gaussian, rng_uniform
17
18 logical :: initialized = .false.
19
20 type(RANDOM_STREAM) :: randomStream
21
22contains
23
24 !--------------------------------------------------------------------------
25 ! rng_Setup
26 !--------------------------------------------------------------------------
27 subroutine rng_setup(seed)
28 !
29 !:Purpose: Initialize the random number generator with a supplied seed.
30 !
31 implicit none
32
33 ! Arguments:
34 integer, intent(in) :: seed
35
36 ! Locals:
37 integer, dimension(1) :: seeds
38 type(RANDOM_STREAM) :: null_stream
39
40 if (initialized) then
41 write(*,*) 'rng_setup: WARNING: you are re-initializing the module!!!'
42 end if
43
44 seeds(1) = seed
45
46 null_stream = RANDOM_STREAM(C_NULL_PTR)
47
48 ! 'seeds' is an array of dimension 1
49 call Ran_R250_new_stream(randomStream, null_stream, seeds, size(seeds))
50 call RanSetSeed_gaussian_stream(randomStream, seeds, size(seeds))
51
52 initialized = .true.
53
54 write(*,*) 'rng_setup: done using seed = ', seed
55
56 end subroutine rng_setup
57
58 !--------------------------------------------------------------------------
59 ! rng_Gaussian
60 !--------------------------------------------------------------------------
61 function rng_gaussian() result(randomNumberGaussian)
62 !
63 !:Purpose: Returns a normally distributed deviate
64 ! with zero mean and unit variance
65 !
66 implicit none
67
68 ! Result:
69 real(8) :: randomNumberGaussian
70
71 randomNumberGaussian = DRan_gaussian_stream(randomStream)
72 end function rng_gaussian
73
74 !--------------------------------------------------------------------------
75 ! random
76 !--------------------------------------------------------------------------
77 function rng_uniform() result(randomNumberUniform)
78 !
79 !:Purpose: Returns a random deviate between 0.0 and 1.0.
80 !
81 implicit none
82
83 ! Result:
84 real(8) :: randomNumberUniform
85
86 randomNumberUniform = DRan_generic_stream(randomStream)
87
88 end function rng_uniform
89
90end module randomNumber_mod
