| 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 1997-2020 Leibniz Universitaet Hannover |
|---|
| 18 | !------------------------------------------------------------------------------! |
|---|
| 19 | ! |
|---|
| 20 | ! Current revisions: |
|---|
| 21 | ! ----------------- |
|---|
| 22 | ! |
|---|
| 23 | ! |
|---|
| 24 | ! Former revisions: |
|---|
| 25 | ! ----------------- |
|---|
| 26 | ! $Id: random_gauss.f90 4360 2020-01-07 11:25:50Z Giersch $ |
|---|
| 27 | ! Corrected "Former revisions" section |
|---|
| 28 | ! |
|---|
| 29 | ! 3655 2019-01-07 16:51:22Z knoop |
|---|
| 30 | ! Corrected "Former revisions" section |
|---|
| 31 | ! |
|---|
| 32 | ! Revision 1.1 1998/03/25 20:09:47 raasch |
|---|
| 33 | ! Initial revision |
|---|
| 34 | ! |
|---|
| 35 | ! |
|---|
| 36 | ! Description: |
|---|
| 37 | ! ------------ |
|---|
| 38 | !> Generates a gaussian distributed random number (mean value 1, sigma = 1) |
|---|
| 39 | !> This routine is taken from the "numerical recipies". |
|---|
| 40 | !------------------------------------------------------------------------------! |
|---|
| 41 | FUNCTION random_gauss( idum, upper_limit ) |
|---|
| 42 | |
|---|
| 43 | |
|---|
| 44 | USE kinds |
|---|
| 45 | |
|---|
| 46 | USE random_function_mod, & |
|---|
| 47 | ONLY: random_function |
|---|
| 48 | |
|---|
| 49 | IMPLICIT NONE |
|---|
| 50 | |
|---|
| 51 | INTEGER(iwp) :: idum !< |
|---|
| 52 | INTEGER(iwp) :: iset !< |
|---|
| 53 | |
|---|
| 54 | REAL(wp) :: fac !< |
|---|
| 55 | REAL(wp) :: gset !< |
|---|
| 56 | REAL(wp) :: random_gauss !< |
|---|
| 57 | REAL(wp) :: rsq !< |
|---|
| 58 | REAL(wp) :: upper_limit !< |
|---|
| 59 | REAL(wp) :: v1 !< |
|---|
| 60 | REAL(wp) :: v2 !< |
|---|
| 61 | |
|---|
| 62 | SAVE iset, gset |
|---|
| 63 | |
|---|
| 64 | DATA iset /0/ |
|---|
| 65 | |
|---|
| 66 | ! |
|---|
| 67 | !-- Random numbers are created as long as they do not fall below the given |
|---|
| 68 | !-- upper limit |
|---|
| 69 | DO |
|---|
| 70 | |
|---|
| 71 | IF ( iset == 0 ) THEN |
|---|
| 72 | rsq = 0.0_wp |
|---|
| 73 | DO WHILE ( rsq >= 1.0_wp .OR. rsq == 0.0_wp ) |
|---|
| 74 | v1 = 2.0_wp * random_function( idum ) - 1.0_wp |
|---|
| 75 | v2 = 2.0_wp * random_function( idum ) - 1.0_wp |
|---|
| 76 | rsq = v1**2 + v2**2 |
|---|
| 77 | ENDDO |
|---|
| 78 | fac = SQRT( -2.0_wp * LOG( rsq ) / rsq ) |
|---|
| 79 | gset = v1 * fac |
|---|
| 80 | random_gauss = v2 * fac + 1.0_wp |
|---|
| 81 | iset = 1 |
|---|
| 82 | ELSE |
|---|
| 83 | random_gauss = gset + 1.0_wp |
|---|
| 84 | iset = 0 |
|---|
| 85 | ENDIF |
|---|
| 86 | |
|---|
| 87 | IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit ) EXIT |
|---|
| 88 | |
|---|
| 89 | ENDDO |
|---|
| 90 | |
|---|
| 91 | END FUNCTION random_gauss |
|---|
