source: palm/trunk/SOURCE/random_function_mod.f90 @ 1851

Last change on this file since 1851 was 1851, checked in by maronga, 5 years ago

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1!> @file random_function_mod.f90
2!--------------------------------------------------------------------------------!
3! This file is part of PALM.
4!
5! PALM is free software: you can redistribute it and/or modify it under the terms
6! of the GNU General Public License as published by the Free Software Foundation,
7! either version 3 of the License, or (at your option) any later version.
8!
9! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
10! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
11! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
12!
13! You should have received a copy of the GNU General Public License along with
14! PALM. If not, see <http://www.gnu.org/licenses/>.
15!
16! Copyright 1997-2016 Leibniz Universitaet Hannover
17!--------------------------------------------------------------------------------!
18!
19! Current revisions:
20! -----------------
21!
22!
23! Former revisions:
24! -----------------
25! $Id: random_function_mod.f90 1851 2016-04-08 13:32:50Z maronga $
26!
27! 1850 2016-04-08 13:29:27Z maronga
28! Module renamed
29!
30!
31! 1682 2015-10-07 23:56:08Z knoop
32! Code annotations made doxygen readable
33!
34! 1342 2014-03-26 17:04:47Z kanani
35! REAL constants defined as wp-kind
36!
37! 1320 2014-03-20 08:40:49Z raasch
38! ONLY-attribute added to USE-statements,
39! kind-parameters added to all INTEGER and REAL declaration statements,
40! kinds are defined in new module kinds,
41! old module precision_kind is removed,
42! revision history before 2012 removed,
43! comment fields (!:) to be used for variable explanations added to
44! all variable declaration statements
45!
46! 1092 2013-02-02 11:24:22Z raasch
47! unused variables removed
48!
49! 1036 2012-10-22 13:43:42Z raasch
50! code put under GPL (PALM 3.9)
51!
52! RCS Log replace by Id keyword, revision history cleaned up
53!
54! Revision 1.1  1998/02/04 16:09:45  raasch
55! Initial revision
56!
57!
58! Description:
59! ------------
60!> Random number generator, produces numbers equally distributed in interval [0,1]
61!> This routine is taken from the "numerical recipies"
62!------------------------------------------------------------------------------!
63 MODULE random_function_mod
64 
65
66    USE kinds
67
68    IMPLICIT NONE
69
70    PRIVATE
71
72    PUBLIC random_function, random_function_ini
73
74    INTEGER(iwp), PUBLIC, SAVE ::  random_iv(32)  !<
75    INTEGER(iwp), PUBLIC, SAVE ::  random_iy      !<
76
77    INTERFACE random_function_ini
78       MODULE PROCEDURE random_function_ini
79    END INTERFACE random_function_ini
80
81    INTERFACE random_function
82       MODULE PROCEDURE random_function
83    END INTERFACE random_function
84
85 CONTAINS
86
87!------------------------------------------------------------------------------!
88! Description:
89! ------------
90!> @todo Missing subroutine description.
91!------------------------------------------------------------------------------!
92    SUBROUTINE random_function_ini
93
94       IMPLICIT NONE
95
96       random_iv = 0
97       random_iy = 0
98
99    END SUBROUTINE random_function_ini
100
101    FUNCTION random_function( idum )
102
103
104       IMPLICIT NONE
105
106       INTEGER(iwp) ::  ia               !<
107       INTEGER(iwp) ::  idum             !<
108       INTEGER(iwp) ::  im               !<
109       INTEGER(iwp) ::  iq               !<
110       INTEGER(iwp) ::  ir               !<
111       INTEGER(iwp) ::  ndiv             !<
112       INTEGER(iwp) ::  ntab             !<
113
114       INTEGER(iwp) ::  j                !<
115       INTEGER(iwp) ::  k                !<
116
117       REAL(wp)     ::  am               !<
118       REAL(wp)     ::  eps              !<
119       REAL(wp)     ::  random_function  !<
120       REAL(wp)     ::  rnmx             !<
121
122       PARAMETER ( ia=16807, im=2147483647, am=1.0_wp/im, iq=127773, ir=2836, &
123                   ntab=32, ndiv=1+(im-1)/ntab, eps=1.2e-7_wp, rnmx=1.0_wp-eps )
124
125       IF ( idum .le. 0  .or.  random_iy .eq. 0 )  THEN
126          idum = max (-idum,1)
127          DO  j = ntab+8,1,-1
128             k    = idum / iq
129             idum = ia * ( idum - k * iq ) - ir * k
130             IF ( idum .lt. 0 )  idum = idum + im
131             IF ( j .le. ntab )  random_iv(j) = idum
132          ENDDO
133          random_iy = random_iv(1)
134       ENDIF
135
136       k    = idum / iq
137       idum = ia * ( idum - k * iq ) - ir * k
138       IF ( idum .lt. 0 )  idum = idum + im
139       j            = 1 + random_iy / ndiv
140       random_iy    = random_iv(j)
141       random_iv(j) = idum
142       random_function  = min ( am * random_iy , rnmx )
143
144    END FUNCTION random_function
145
146 END MODULE random_function_mod
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