| 1 | !> @file random_gauss.f90 |
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| 2 | !--------------------------------------------------------------------------------------------------! |
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| 3 | ! This file is part of the PALM model system. |
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| 4 | ! |
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| 5 | ! PALM is free software: you can redistribute it and/or modify it under the terms of the GNU General |
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| 6 | ! Public License as published by the Free Software Foundation, either version 3 of the License, or |
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| 7 | ! (at your option) any later version. |
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| 8 | ! |
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| 9 | ! PALM is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the |
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| 10 | ! implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General |
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| 11 | ! Public License for more details. |
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| 12 | ! |
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| 13 | ! You should have received a copy of the GNU General Public License along with PALM. If not, see |
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| 14 | ! <http://www.gnu.org/licenses/>. |
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| 15 | ! |
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| 16 | ! Copyright 1997-2021 Leibniz Universitaet Hannover |
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| 17 | !--------------------------------------------------------------------------------------------------! |
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| 18 | ! |
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| 19 | ! |
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| 20 | ! Current revisions: |
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| 21 | ! ----------------- |
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| 22 | ! |
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| 23 | ! |
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| 24 | ! Former revisions: |
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| 25 | ! ----------------- |
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| 26 | ! $Id: random_gauss.f90 4828 2021-01-05 11:21:41Z Giersch $ |
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| 27 | ! File re-formatted to follow the PALM coding standard |
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| 28 | ! |
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| 29 | ! 4360 2020-01-07 11:25:50Z suehring |
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| 30 | ! Corrected "Former revisions" section |
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| 31 | ! |
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| 32 | ! 3655 2019-01-07 16:51:22Z knoop |
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| 33 | ! Corrected "Former revisions" section |
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| 34 | ! |
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| 35 | ! Revision 1.1 1998/03/25 20:09:47 raasch |
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| 36 | ! Initial revision |
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| 37 | ! |
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| 38 | ! |
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| 39 | !--------------------------------------------------------------------------------------------------! |
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| 40 | ! Description: |
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| 41 | ! ------------ |
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| 42 | !> Generates a gaussian distributed random number (mean value 1, sigma = 1) |
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| 43 | !> This routine is taken from the "numerical recipies". |
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| 44 | !--------------------------------------------------------------------------------------------------! |
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| 45 | FUNCTION random_gauss( idum, upper_limit ) |
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| 46 | |
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| 47 | |
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| 48 | USE kinds |
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| 49 | |
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| 50 | USE random_function_mod, & |
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| 51 | ONLY: random_function |
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| 52 | |
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| 53 | IMPLICIT NONE |
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| 54 | |
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| 55 | INTEGER(iwp) :: idum !< |
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| 56 | INTEGER(iwp) :: iset !< |
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| 57 | |
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| 58 | REAL(wp) :: fac !< |
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| 59 | REAL(wp) :: gset !< |
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| 60 | REAL(wp) :: random_gauss !< |
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| 61 | REAL(wp) :: rsq !< |
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| 62 | REAL(wp) :: upper_limit !< |
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| 63 | REAL(wp) :: v1 !< |
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| 64 | REAL(wp) :: v2 !< |
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| 65 | |
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| 66 | SAVE iset, gset |
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| 67 | |
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| 68 | DATA iset /0/ |
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| 69 | |
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| 70 | ! |
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| 71 | !-- Random numbers are created as long as they do not fall below the given upper limit |
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| 72 | DO |
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| 73 | |
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| 74 | IF ( iset == 0 ) THEN |
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| 75 | rsq = 0.0_wp |
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| 76 | DO WHILE ( rsq >= 1.0_wp .OR. rsq == 0.0_wp ) |
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| 77 | v1 = 2.0_wp * random_function( idum ) - 1.0_wp |
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| 78 | v2 = 2.0_wp * random_function( idum ) - 1.0_wp |
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| 79 | rsq = v1**2 + v2**2 |
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| 80 | ENDDO |
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| 81 | fac = SQRT( -2.0_wp * LOG( rsq ) / rsq ) |
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| 82 | gset = v1 * fac |
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| 83 | random_gauss = v2 * fac + 1.0_wp |
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| 84 | iset = 1 |
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| 85 | ELSE |
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| 86 | random_gauss = gset + 1.0_wp |
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| 87 | iset = 0 |
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| 88 | ENDIF |
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| 89 | |
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| 90 | IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit ) EXIT |
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| 91 | |
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| 92 | ENDDO |
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| 93 | |
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| 94 | END FUNCTION random_gauss |
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