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 3655 2019-01-07 16:51:22Z raasch $ |
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27 | ! Corrected "Former revisions" section |
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28 | ! |
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29 | ! 2696 2017-12-14 17:12:51Z kanani |
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30 | ! Change in file header (GPL part) |
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31 | ! |
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32 | ! 2101 2017-01-05 16:42:31Z suehring |
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33 | ! |
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34 | ! 2000 2016-08-20 18:09:15Z knoop |
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35 | ! Forced header and separation lines into 80 columns |
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36 | ! |
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37 | ! 1682 2015-10-07 23:56:08Z knoop |
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38 | ! Code annotations made doxygen readable |
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39 | ! |
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40 | ! 1342 2014-03-26 17:04:47Z kanani |
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41 | ! REAL constants defined as wp-kind |
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42 | ! |
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43 | ! 1320 2014-03-20 08:40:49Z raasch |
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44 | ! ONLY-attribute added to USE-statements, |
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45 | ! kind-parameters added to all INTEGER and REAL declaration statements, |
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46 | ! kinds are defined in new module kinds, |
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47 | ! old module precision_kind is removed, |
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48 | ! revision history before 2012 removed, |
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49 | ! comment fields (!:) to be used for variable explanations added to |
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50 | ! all variable declaration statements |
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51 | ! |
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52 | ! 1036 2012-10-22 13:43:42Z raasch |
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53 | ! code put under GPL (PALM 3.9) |
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54 | ! |
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55 | ! RCS Log replace by Id keyword, revision history cleaned up |
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56 | ! |
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57 | ! Revision 1.1 1998/03/25 20:09:47 raasch |
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58 | ! Initial revision |
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59 | ! |
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60 | ! |
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61 | ! Description: |
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62 | ! ------------ |
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63 | !> Generates a gaussian distributed random number (mean value 1, sigma = 1) |
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64 | !> This routine is taken from the "numerical recipies". |
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65 | !------------------------------------------------------------------------------! |
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66 | FUNCTION random_gauss( idum, upper_limit ) |
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67 | |
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68 | |
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69 | USE kinds |
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70 | |
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71 | USE random_function_mod, & |
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72 | ONLY: random_function |
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73 | |
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74 | IMPLICIT NONE |
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75 | |
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76 | INTEGER(iwp) :: idum !< |
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77 | INTEGER(iwp) :: iset !< |
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78 | |
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79 | REAL(wp) :: fac !< |
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80 | REAL(wp) :: gset !< |
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81 | REAL(wp) :: random_gauss !< |
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82 | REAL(wp) :: rsq !< |
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83 | REAL(wp) :: upper_limit !< |
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84 | REAL(wp) :: v1 !< |
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85 | REAL(wp) :: v2 !< |
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86 | |
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87 | SAVE iset, gset |
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88 | |
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89 | DATA iset /0/ |
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90 | |
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91 | ! |
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92 | !-- Random numbers are created as long as they do not fall below the given |
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93 | !-- upper limit |
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94 | DO |
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95 | |
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96 | IF ( iset == 0 ) THEN |
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97 | rsq = 0.0_wp |
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98 | DO WHILE ( rsq >= 1.0_wp .OR. rsq == 0.0_wp ) |
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99 | v1 = 2.0_wp * random_function( idum ) - 1.0_wp |
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100 | v2 = 2.0_wp * random_function( idum ) - 1.0_wp |
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101 | rsq = v1**2 + v2**2 |
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102 | ENDDO |
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103 | fac = SQRT( -2.0_wp * LOG( rsq ) / rsq ) |
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104 | gset = v1 * fac |
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105 | random_gauss = v2 * fac + 1.0_wp |
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106 | iset = 1 |
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107 | ELSE |
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108 | random_gauss = gset + 1.0_wp |
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109 | iset = 0 |
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110 | ENDIF |
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111 | |
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112 | IF ( ABS( random_gauss - 1.0_wp ) <= upper_limit ) EXIT |
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113 | |
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114 | ENDDO |
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115 | |
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116 | END FUNCTION random_gauss |
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