source: palm/trunk/SOURCE/random_gauss.f90 @ 1037

Last change on this file since 1037 was 1037, checked in by raasch, 9 years ago

last commit documented

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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 1997-2012  Leibniz University Hannover
18!--------------------------------------------------------------------------------!
19!
20! Current revisions:
21! -----------------
22!
23!
24! Former revisions:
25! -----------------
26! $Id: random_gauss.f90 1037 2012-10-22 14:10:22Z raasch $
27!
28! 1036 2012-10-22 13:43:42Z raasch
29! code put under GPL (PALM 3.9)
30!
31! RCS Log replace by Id keyword, revision history cleaned up
32!
33! Revision 1.4  2006/08/04 15:01:48  raasch
34! Range of random number is limited by an upper limit (new second parameter)
35!
36! Revision 1.1  1998/03/25 20:09:47  raasch
37! Initial revision
38!
39!
40! Description:
41! ------------
42! Generates a gaussian distributed random number (mean value 1, sigma = 1)
43! This routine is taken from the "numerical recipies".
44!------------------------------------------------------------------------------!
45
46    USE random_function_mod
47
48    IMPLICIT NONE
49
50    INTEGER :: idum, iset
51    REAL    :: fac, gset, random_gauss, rsq, upper_limit, v1, v2
52
53    SAVE  iset, gset
54
55    DATA  iset /0/
56
57!
58!-- Random numbers are created as long as they do not fall below the given
59!-- upper limit
60    DO
61
62       IF ( iset == 0 )  THEN
63          rsq = 0.0
64          DO  WHILE ( rsq >= 1.0  .OR.  rsq == 0.0 )
65             v1  = 2.0 * random_function( idum ) - 1.0
66             v2  = 2.0 * random_function( idum ) - 1.0
67             rsq = v1**2 + v2**2
68          ENDDO
69          fac          = SQRT( -2.0 * LOG( rsq ) / rsq )
70          gset         = v1 * fac
71          random_gauss = v2 * fac + 1.0
72          iset         = 1
73       ELSE
74          random_gauss = gset + 1.0
75          iset         = 0
76       ENDIF
77
78       IF ( ABS( random_gauss - 1.0 ) <= upper_limit )  EXIT
79
80    ENDDO
81
82 END FUNCTION random_gauss
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