source: palm/trunk/SOURCE/random_gauss.f90 @ 2101

Last change on this file since 2101 was 2101, checked in by suehring, 5 years ago

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1!> @file random_gauss.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
6! terms of the GNU General Public License as published by the Free Software
7! Foundation, either version 3 of the License, or (at your option) any later
8! version.
9!
10! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
11! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
12! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
13!
14! You should have received a copy of the GNU General Public License along with
15! PALM. If not, see <http://www.gnu.org/licenses/>.
16!
17! Copyright 1997-2017 Leibniz Universitaet Hannover
18!------------------------------------------------------------------------------!
19!
20! Current revisions:
21! -----------------
22!
23!
24! Former revisions:
25! -----------------
26! $Id: random_gauss.f90 2101 2017-01-05 16:42:31Z suehring $
27!
28! 2000 2016-08-20 18:09:15Z knoop
29! Forced header and separation lines into 80 columns
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! 1036 2012-10-22 13:43:42Z raasch
47! code put under GPL (PALM 3.9)
48!
49! RCS Log replace by Id keyword, revision history cleaned up
50!
51! Revision 1.1  1998/03/25 20:09:47  raasch
52! Initial revision
53!
54!
55! Description:
56! ------------
57!> Generates a gaussian distributed random number (mean value 1, sigma = 1)
58!> This routine is taken from the "numerical recipies".
59!------------------------------------------------------------------------------!
60 FUNCTION random_gauss( idum, upper_limit )
61 
62
63    USE kinds
64
65    USE random_function_mod,                                                   &
66        ONLY:  random_function
67
68    IMPLICIT NONE
69
70    INTEGER(iwp) ::  idum          !<
71    INTEGER(iwp) ::  iset          !<
72
73    REAL(wp)     ::  fac           !<
74    REAL(wp)     ::  gset          !<
75    REAL(wp)     ::  random_gauss  !<
76    REAL(wp)     ::  rsq           !<
77    REAL(wp)     ::  upper_limit   !<
78    REAL(wp)     ::  v1            !<
79    REAL(wp)     ::  v2            !<
80
81    SAVE  iset, gset
82
83    DATA  iset /0/
84
85!
86!-- Random numbers are created as long as they do not fall below the given
87!-- upper limit
88    DO
89
90       IF ( iset == 0 )  THEN
91          rsq = 0.0_wp
92          DO  WHILE ( rsq >= 1.0_wp  .OR.  rsq == 0.0_wp )
93             v1  = 2.0_wp * random_function( idum ) - 1.0_wp
94             v2  = 2.0_wp * random_function( idum ) - 1.0_wp
95             rsq = v1**2 + v2**2
96          ENDDO
97          fac          = SQRT( -2.0_wp * LOG( rsq ) / rsq )
98          gset         = v1 * fac
99          random_gauss = v2 * fac + 1.0_wp
100          iset         = 1
101       ELSE
102          random_gauss = gset + 1.0_wp
103          iset         = 0
104       ENDIF
105
106       IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit )  EXIT
107
108    ENDDO
109
110 END FUNCTION random_gauss
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