source: palm/trunk/SOURCE/random_gauss.f90 @ 4180

Last change on this file since 4180 was 4180, checked in by scharf, 22 months ago

removed comments in 'Former revisions' section that are older than 01.01.2019

  • Property svn:keywords set to Id
File size: 2.5 KB
Line 
1!> @file random_gauss.f90
2!------------------------------------------------------------------------------!
3! This file is part of the PALM model system.
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 1997-2019 Leibniz Universitaet Hannover
18!------------------------------------------------------------------------------!
19!
20! Current revisions:
21! -----------------
22!
23!
24! Former revisions:
25! -----------------
26! $Id: random_gauss.f90 4180 2019-08-21 14:37:54Z scharf $
27! Corrected "Former revisions" section
28!
29!
30! Description:
31! ------------
32!> Generates a gaussian distributed random number (mean value 1, sigma = 1)
33!> This routine is taken from the "numerical recipies".
34!------------------------------------------------------------------------------!
35 FUNCTION random_gauss( idum, upper_limit )
36 
37
38    USE kinds
39
40    USE random_function_mod,                                                   &
41        ONLY:  random_function
42
43    IMPLICIT NONE
44
45    INTEGER(iwp) ::  idum          !<
46    INTEGER(iwp) ::  iset          !<
47
48    REAL(wp)     ::  fac           !<
49    REAL(wp)     ::  gset          !<
50    REAL(wp)     ::  random_gauss  !<
51    REAL(wp)     ::  rsq           !<
52    REAL(wp)     ::  upper_limit   !<
53    REAL(wp)     ::  v1            !<
54    REAL(wp)     ::  v2            !<
55
56    SAVE  iset, gset
57
58    DATA  iset /0/
59
60!
61!-- Random numbers are created as long as they do not fall below the given
62!-- upper limit
63    DO
64
65       IF ( iset == 0 )  THEN
66          rsq = 0.0_wp
67          DO  WHILE ( rsq >= 1.0_wp  .OR.  rsq == 0.0_wp )
68             v1  = 2.0_wp * random_function( idum ) - 1.0_wp
69             v2  = 2.0_wp * random_function( idum ) - 1.0_wp
70             rsq = v1**2 + v2**2
71          ENDDO
72          fac          = SQRT( -2.0_wp * LOG( rsq ) / rsq )
73          gset         = v1 * fac
74          random_gauss = v2 * fac + 1.0_wp
75          iset         = 1
76       ELSE
77          random_gauss = gset + 1.0_wp
78          iset         = 0
79       ENDIF
80
81       IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit )  EXIT
82
83    ENDDO
84
85 END FUNCTION random_gauss
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