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1 ## Copyright (C) 1995, 1996 Kurt Hornik |
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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 2, or (at your option) |
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8 ## 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, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} cross (@var{x}, @var{y}, @var{dim}) |
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22 ## Computes the vector cross product of the two 3-dimensional vectors |
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23 ## @var{x} and @var{y}. |
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24 ## |
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25 ## @example |
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26 ## @group |
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27 ## cross ([1,1,0], [0,1,1]) |
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28 ## @result{} [ 1; -1; 1 ] |
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29 ## @end group |
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30 ## @end example |
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31 ## |
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32 ## If @var{x} and @var{y} are matrices, the cross product is applied |
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33 ## along the first dimension with 3 elements. The optional argument |
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34 ## @var{dim} is used to force the cross product to be calculated along |
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35 ## the dimension defined by @var{dim}. |
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36 ## @end deftypefn |
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37 |
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38 ## Author: Kurt Hornik <Kurt.Hornik@wu-wien.ac.at> |
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39 ## Created: 15 October 1994 |
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40 ## Adapted-By: jwe |
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41 |
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42 function z = cross (x, y, dim) |
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43 |
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44 if (nargin != 2 && nargin != 3) |
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45 usage ("cross (x, y, dim)"); |
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46 endif |
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47 |
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48 if (ndims (x) < 3 && ndims (y) < 3 && nargin < 3) |
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49 ## COMPATIBILITY -- opposite behaviour for cross(row,col) |
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50 ## Swap x and y in the assignments below to get the matlab behaviour. |
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51 ## Better yet, fix the calling code so that it uses conformant vectors. |
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52 if (columns (x) == 1 && rows (y) == 1) |
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53 warning ("cross: taking cross product of column by row"); |
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54 y = y.'; |
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55 elseif (rows (x) == 1 && columns (y) == 1) |
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56 warning ("cross: taking cross product of row by column"); |
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57 x = x.'; |
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58 endif |
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59 endif |
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60 |
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61 if (nargin == 2) |
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62 dim = find (size (x) == 3, 1); |
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63 if (isempty (dim)) |
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64 error ("cross: must have at least one dimension with 3 elements"); |
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65 endif |
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66 else |
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67 if (size (x) != 3) |
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68 error ("cross: dimension dim must have 3 elements"); |
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69 endif |
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70 endif |
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71 |
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72 nd = ndims (x); |
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73 sz = size (x); |
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74 idx1 = cell (1, nd); |
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75 for i = 1:nd |
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76 idx1{i} = 1:sz(i); |
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77 endfor |
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78 idx2 = idx3 = idx1; |
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79 idx1(dim) = 1; |
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80 idx2(dim) = 2; |
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81 idx3(dim) = 3; |
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82 |
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83 if (size (x) == size (y)) |
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84 z = cat (dim, |
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85 (x(idx2{:}) .* y(idx3{:}) - x(idx3{:}) .* y(idx2{:})), |
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86 (x(idx3{:}) .* y(idx1{:}) - x(idx1{:}) .* y(idx3{:})), |
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87 (x(idx1{:}) .* y(idx2{:}) - x(idx2{:}) .* y(idx1{:}))); |
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88 else |
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89 error ("cross: x and y must have the same dimensions"); |
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90 endif |
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91 |
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92 endfunction |
