| 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 |
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| 6 | ! terms of the GNU General Public License as published by the Free Software |
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| 7 | ! Foundation, either version 3 of the License, or (at your option) any later |
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| 8 | ! version. |
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| 9 | ! |
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| 10 | ! PALM is distributed in the hope that it will be useful, but WITHOUT ANY |
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| 11 | ! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR |
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| 12 | ! A PARTICULAR PURPOSE. See the GNU General Public License for more details. |
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| 13 | ! |
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| 14 | ! You should have received a copy of the GNU General Public License along with |
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| 15 | ! PALM. If not, see <http://www.gnu.org/licenses/>. |
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| 16 | ! |
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| 17 | ! Copyright 1997-2019 Leibniz Universitaet Hannover |
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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 4180 2019-08-21 14:37:54Z raasch $ |
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| 27 | ! Corrected "Former revisions" section |
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| 28 | ! |
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| 29 | ! |
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| 30 | ! Description: |
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| 31 | ! ------------ |
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| 32 | !> Generates a gaussian distributed random number (mean value 1, sigma = 1) |
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| 33 | !> This routine is taken from the "numerical recipies". |
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| 34 | !------------------------------------------------------------------------------! |
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| 35 | FUNCTION random_gauss( idum, upper_limit ) |
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| 36 | |
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| 37 | |
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| 38 | USE kinds |
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| 39 | |
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| 40 | USE random_function_mod, & |
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| 41 | ONLY: random_function |
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| 42 | |
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| 43 | IMPLICIT NONE |
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| 44 | |
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| 45 | INTEGER(iwp) :: idum !< |
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| 46 | INTEGER(iwp) :: iset !< |
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| 47 | |
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| 48 | REAL(wp) :: fac !< |
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| 49 | REAL(wp) :: gset !< |
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| 50 | REAL(wp) :: random_gauss !< |
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| 51 | REAL(wp) :: rsq !< |
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| 52 | REAL(wp) :: upper_limit !< |
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| 53 | REAL(wp) :: v1 !< |
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| 54 | REAL(wp) :: v2 !< |
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| 55 | |
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| 56 | SAVE iset, gset |
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| 57 | |
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| 58 | DATA iset /0/ |
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| 59 | |
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| 60 | ! |
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| 61 | !-- Random numbers are created as long as they do not fall below the given |
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| 62 | !-- upper limit |
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| 63 | DO |
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| 64 | |
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| 65 | IF ( iset == 0 ) THEN |
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| 66 | rsq = 0.0_wp |
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| 67 | DO WHILE ( rsq >= 1.0_wp .OR. rsq == 0.0_wp ) |
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| 68 | v1 = 2.0_wp * random_function( idum ) - 1.0_wp |
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| 69 | v2 = 2.0_wp * random_function( idum ) - 1.0_wp |
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| 70 | rsq = v1**2 + v2**2 |
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| 71 | ENDDO |
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| 72 | fac = SQRT( -2.0_wp * LOG( rsq ) / rsq ) |
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| 73 | gset = v1 * fac |
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| 74 | random_gauss = v2 * fac + 1.0_wp |
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| 75 | iset = 1 |
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| 76 | ELSE |
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| 77 | random_gauss = gset + 1.0_wp |
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| 78 | iset = 0 |
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| 79 | ENDIF |
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| 80 | |
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| 81 | IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit ) EXIT |
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| 82 | |
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| 83 | ENDDO |
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| 84 | |
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| 85 | END FUNCTION random_gauss |
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