source: palm/trunk/SOURCE/random_gauss.f90 @ 1320

Last change on this file since 1320 was 1320, checked in by raasch, 10 years ago

ONLY-attribute added to USE-statements,
kind-parameters added to all INTEGER and REAL declaration statements,
kinds are defined in new module kinds,
old module precision_kind is removed,
revision history before 2012 removed,
comment fields (!:) to be used for variable explanations added to all variable declaration statements

  • Property svn:keywords set to Id
File size: 3.0 KB
Line 
1 FUNCTION random_gauss( idum, upper_limit )
2
3!--------------------------------------------------------------------------------!
4! This file is part of PALM.
5!
6! PALM is free software: you can redistribute it and/or modify it under the terms
7! of the GNU General Public License as published by the Free Software Foundation,
8! either version 3 of the License, or (at your option) any later 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 1997-2014 Leibniz Universitaet Hannover
18!--------------------------------------------------------------------------------!
19!
20! Current revisions:
21! -----------------
22! ONLY-attribute added to USE-statements,
23! kind-parameters added to all INTEGER and REAL declaration statements,
24! kinds are defined in new module kinds,
25! old module precision_kind is removed,
26! revision history before 2012 removed,
27! comment fields (!:) to be used for variable explanations added to
28! all variable declaration statements
29!
30! Former revisions:
31! -----------------
32! $Id: random_gauss.f90 1320 2014-03-20 08:40:49Z raasch $
33!
34! 1036 2012-10-22 13:43:42Z raasch
35! code put under GPL (PALM 3.9)
36!
37! RCS Log replace by Id keyword, revision history cleaned up
38!
39! Revision 1.1  1998/03/25 20:09:47  raasch
40! Initial revision
41!
42!
43! Description:
44! ------------
45! Generates a gaussian distributed random number (mean value 1, sigma = 1)
46! This routine is taken from the "numerical recipies".
47!------------------------------------------------------------------------------!
48
49    USE kinds
50
51    USE random_function_mod,                                                   &
52        ONLY:  random_function
53
54    IMPLICIT NONE
55
56    INTEGER(iwp) ::  idum          !:
57    INTEGER(iwp) ::  iset          !:
58
59    REAL(wp)     ::  fac           !:
60    REAL(wp)     ::  gset          !:
61    REAL(wp)     ::  random_gauss  !:
62    REAL(wp)     ::  rsq           !:
63    REAL(wp)     ::  upper_limit   !:
64    REAL(wp)     ::  v1            !:
65    REAL(wp)     ::  v2            !:
66
67    SAVE  iset, gset
68
69    DATA  iset /0/
70
71!
72!-- Random numbers are created as long as they do not fall below the given
73!-- upper limit
74    DO
75
76       IF ( iset == 0 )  THEN
77          rsq = 0.0
78          DO  WHILE ( rsq >= 1.0  .OR.  rsq == 0.0 )
79             v1  = 2.0 * random_function( idum ) - 1.0
80             v2  = 2.0 * random_function( idum ) - 1.0
81             rsq = v1**2 + v2**2
82          ENDDO
83          fac          = SQRT( -2.0 * LOG( rsq ) / rsq )
84          gset         = v1 * fac
85          random_gauss = v2 * fac + 1.0
86          iset         = 1
87       ELSE
88          random_gauss = gset + 1.0
89          iset         = 0
90       ENDIF
91
92       IF ( ABS( random_gauss - 1.0 ) <= upper_limit )  EXIT
93
94    ENDDO
95
96 END FUNCTION random_gauss
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