annotate scripts/geometry/tsearchn.m @ 27919:1891570abac8

update Octave Project Developers copyright for the new year In files that have the "Octave Project Developers" copyright notice, update for 2020.
author John W. Eaton <jwe@octave.org>
date Mon, 06 Jan 2020 22:29:51 -0500
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1891570abac8 update Octave Project Developers copyright for the new year
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1 ## Copyright (C) 2007-2020 The Octave Project Developers
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2 ##
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3 ## See the file COPYRIGHT.md in the top-level directory of this distribution
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4 ## or <https://octave.org/COPYRIGHT.html/>.
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5 ##
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6 ##
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7 ## This file is part of Octave.
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8 ##
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9 ## Octave is free software: you can redistribute it and/or modify it
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10 ## under the terms of the GNU General Public License as published by
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11 ## the Free Software Foundation, either version 3 of the License, or
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12 ## (at your option) any later version.
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13 ##
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14 ## Octave is distributed in the hope that it will be useful, but
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15 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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16 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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17 ## GNU General Public License for more details.
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18 ##
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19 ## You should have received a copy of the GNU General Public License
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20 ## along with Octave; see the file COPYING. If not, see
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21 ## <https://www.gnu.org/licenses/>.
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22
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23 ## -*- texinfo -*-
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24 ## @deftypefn {} {@var{idx} =} tsearchn (@var{x}, @var{t}, @var{xi})
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25 ## @deftypefnx {} {[@var{idx}, @var{p}] =} tsearchn (@var{x}, @var{t}, @var{xi})
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26 ## Search for the enclosing Delaunay convex hull.
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27 ##
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28 ## For @code{@var{t} = delaunayn (@var{x})}, finds the index in @var{t}
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29 ## containing the points @var{xi}. For points outside the convex hull,
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30 ## @var{idx} is NaN.
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31 ##
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32 ## If requested @code{tsearchn} also returns the Barycentric coordinates
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33 ## @var{p} of the enclosing triangles.
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34 ## @seealso{delaunay, delaunayn}
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35 ## @end deftypefn
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36
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37 function [idx, p] = tsearchn (x, t, xi)
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38
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39 if (nargin != 3)
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40 print_usage ();
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41 endif
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42
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43 nt = rows (t);
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44 [m, n] = size (x);
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45 mi = rows (xi);
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46 idx = NaN (mi, 1);
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47 p = NaN (mi, n + 1);
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48
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49 ni = [1:mi].';
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50 for i = 1 : nt
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51 ## Only calculate the Barycentric coordinates for points that have not
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52 ## already been found in a triangle.
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53 b = cart2bary (x (t (i, :), :), xi(ni,:));
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54
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55 ## Our points xi are in the current triangle if
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56 ## (all (b >= 0) && all (b <= 1)). However as we impose that
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57 ## sum (b,2) == 1 we only need to test all(b>=0). Note need to add
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58 ## a small margin for rounding errors
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59 intri = all (b >= -1e-12, 2);
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60 idx(ni(intri)) = i;
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61 p(ni(intri),:) = b(intri, :);
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62 ni(intri) = [];
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63 endfor
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64
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65 endfunction
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66
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67 function Beta = cart2bary (T, P)
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68 ## Conversion of Cartesian to Barycentric coordinates.
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69 ## Given a reference simplex in N dimensions represented by an
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70 ## N+1-by-N matrix, an arbitrary point P in Cartesian coordinates,
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71 ## represented by an N-by-1 column vector can be written as
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72 ##
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73 ## P = Beta * T
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74 ##
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75 ## Where Beta is an N+1 vector of the barycentric coordinates. A criteria
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76 ## on Beta is that
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77 ##
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78 ## sum (Beta) == 1
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79 ##
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80 ## and therefore we can write the above as
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81 ##
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82 ## P - T(end, :) = Beta(1:end-1) * (T(1:end-1,:) - ones (N,1) * T(end,:))
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83 ##
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84 ## and then we can solve for Beta as
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85 ##
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86 ## Beta(1:end-1) = (P - T(end,:)) / (T(1:end-1,:) - ones (N,1) * T(end,:))
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87 ## Beta(end) = sum (Beta)
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88 ##
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89 ## Note code below is generalized for multiple values of P, one per row.
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90 [M, N] = size (P);
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91 Beta = (P - ones (M,1) * T(end,:)) / (T(1:end-1,:) - ones (N,1) * T(end,:));
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92 Beta (:,end+1) = 1 - sum (Beta, 2);
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93
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94 endfunction
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95
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96
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97 %!shared x, tri
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98 %! x = [-1,-1;-1,1;1,-1];
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99 %! tri = [1, 2, 3];
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100 %!test
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101 %! [idx, p] = tsearchn (x,tri,[-1,-1]);
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102 %! assert (idx, 1);
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103 %! assert (p, [1,0,0], 1e-12);
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104 %!test
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105 %! [idx, p] = tsearchn (x,tri,[-1,1]);
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106 %! assert (idx, 1);
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107 %! assert (p, [0,1,0], 1e-12);
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108 %!test
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109 %! [idx, p] = tsearchn (x,tri,[1,-1]);
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110 %! assert (idx, 1);
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111 %! assert (p, [0,0,1], 1e-12);
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112 %!test
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113 %! [idx, p] = tsearchn (x,tri,[-1/3,-1/3]);
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114 %! assert (idx, 1);
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115 %! assert (p, [1/3,1/3,1/3], 1e-12);
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116 %!test
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117 %! [idx, p] = tsearchn (x,tri,[1,1]);
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118 %! assert (idx, NaN);
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119 %! assert (p, [NaN, NaN, NaN]);