annotate scripts/general/divergence.m @ 19867:9fc020886ae9

maint: Clean up m-files to follow Octave coding conventions. Try to trim long lines to < 80 chars. Use '##' for single line comments. Use '(...)' around tests for if/elseif/switch/while. Abut cell indexing operator '{' next to variable. Abut array indexing operator '(' next to variable. Use space between negation operator '!' and following expression. Use two newlines between endfunction and start of %!test or %!demo code. Remove unnecessary parens grouping between short-circuit operators. Remove stray extra spaces (typos) between variables and assignment operators. Remove stray extra spaces from ends of lines.
author Rik <rik@octave.org>
date Mon, 23 Feb 2015 14:54:39 -0800
parents 4197fc428c7d
children 7503499a252b
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1 ## Copyright (C) 2009-2015 Kai Habel
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {@var{div} =} divergence (@var{x}, @var{y}, @var{z}, @var{fx}, @var{fy}, @var{fz})
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21 ## @deftypefnx {Function File} {@var{div} =} divergence (@var{fx}, @var{fy}, @var{fz})
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22 ## @deftypefnx {Function File} {@var{div} =} divergence (@var{x}, @var{y}, @var{fx}, @var{fy})
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23 ## @deftypefnx {Function File} {@var{div} =} divergence (@var{fx}, @var{fy})
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24 ## Calculate divergence of a vector field given by the arrays @var{fx},
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25 ## @var{fy}, and @var{fz} or @var{fx}, @var{fy} respectively.
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26 ## @tex
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27 ## $$
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28 ## div F(x,y,z) = \partial_x{F} + \partial_y{F} + \partial_z{F}
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29 ## $$
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30 ## @end tex
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31 ## @ifnottex
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32 ##
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33 ## @example
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34 ## @group
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35 ## d d d
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36 ## div F(x,y,z) = -- F(x,y,z) + -- F(x,y,z) + -- F(x,y,z)
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37 ## dx dy dz
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38 ## @end group
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39 ## @end example
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40 ##
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41 ## @end ifnottex
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42 ## The coordinates of the vector field can be given by the arguments @var{x},
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43 ## @var{y}, @var{z} or @var{x}, @var{y} respectively.
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44 ##
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45 ## @seealso{curl, gradient, del2, dot}
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46 ## @end deftypefn
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47
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48 ## Author: Kai Habel <kai.habel@gmx.de>
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49
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50 function retval = divergence (varargin)
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51
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52 fidx = 1;
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53 if (nargin == 2)
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54 sz = size (varargin{fidx});
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55 dx = (1:sz(2))(:);
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56 dy = (1:sz(1))(:);
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57 elseif (nargin == 3)
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58 sz = size (varargin{fidx});
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59 dx = 1:sz(2);
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60 dy = 1:sz(1);
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61 dz = 1:sz(3);
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62 elseif (nargin == 4)
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63 fidx = 3;
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64 dx = varargin{1}(1,:);
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65 dy = varargin{2}(:,1);
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66 elseif (nargin == 6)
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67 fidx = 4;
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68 dx = varargin{1}(1,:,1)(:);
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69 dy = varargin{2}(:,1,1)(:);
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70 dz = varargin{3}(1,1,:)(:);
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71 else
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72 print_usage ();
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73 endif
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74
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75 if (nargin == 4 || nargin == 2)
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76 if (! size_equal (varargin{fidx},varargin{fidx + 1}))
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77 error ("divergence: size of X and Y must match");
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78 elseif (ndims (varargin{fidx}) != 2)
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79 error ("divergence: expected two-dimensional matrices X and Y");
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80 elseif (length (dx) != columns (varargin{fidx})
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81 || length (dy) != rows (varargin{fidx}))
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82 error ("divergence: size of dx and dy must match the respective dimension of X and Y");
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83 endif
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84
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85 retval = gradient (varargin{fidx}, dx, dy);
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86 retval += gradient (varargin{fidx + 1}.', dy, dx).';
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87
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88 elseif (nargin == 6 || nargin == 3)
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89 if (! size_equal (varargin{fidx},varargin{fidx + 1},varargin{fidx + 2}))
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90 error ("divergence: size of X, Y, and Z must match");
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91 elseif (ndims (varargin{fidx}) != 3)
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92 error ("divergence: expected two-dimensional matrices X, Y, and Z");
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93 elseif ((length (dx) != size (varargin{fidx}, 2))
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94 || (length (dy) != size (varargin{fidx}, 1))
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95 || (length (dz) != size (varargin{fidx}, 3)))
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96 error ("divergence: size of dx, dy, and dz must match the respective dimesion of X, Y, and Z");
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97 endif
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98
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99 ## x-direction
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100 retval = gradient (varargin{fidx}, dx, dy, dz);
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101 ## y-direction
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102 retval += shiftdim (gradient (shiftdim (varargin{fidx + 1}, 2), dy), 1);
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103 ## z-direction
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104 retval += shiftdim (gradient (shiftdim (varargin{fidx + 2}, 1), dz), 2);
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105 endif
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106
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107 endfunction
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108
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109
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110 %!test
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111 %! [X,Y] = meshgrid (-20:20,-22:22);
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112 %! div = divergence (X-Y,Y);
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113 %! assert (all (div(:) == 2));
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114 %! assert (size_equal (X,Y,div));
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115