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1 ## Copyright (C) 2000 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 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 {Loadable Function} {@var{H} =} convhull (@var{x}, @var{y}) |
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22 ## @deftypefnx {Loadable Function} {@var{H} =} convhull (@var{x}, @var{y}, @var{opt}) |
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23 ## Returns the index vector to the points of the enclosing convex hull. The |
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24 ## data points are defined by the x and y vectors. |
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25 ## |
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26 ## A third optional argument, which must be a string, contains extra options |
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27 ## passed to the underlying qhull command. See the documentation for the |
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28 ## Qhull library for details. |
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29 ## |
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30 ## @seealso{delaunay, convhulln} |
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31 ## @end deftypefn |
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32 |
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33 ## Author: Kai Habel <kai.habel@gmx.de> |
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34 |
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35 function H = convhull (x, y, opt) |
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36 |
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37 if (nargin != 2 && nargin != 3) |
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38 print_usage (); |
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39 endif |
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40 |
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41 if (isvector (x) && isvector (y) && length (x) == length (y)) |
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42 if (nargin == 2) |
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43 i = convhulln ([x(:), y(:)]); |
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44 elseif (ischar (opt) || iscell (opt)) |
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45 i = convhulln ([x(:), y(:)], opt); |
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46 else |
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47 error ("convhull: third argument must be a string or cell array of strings"); |
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48 endif |
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49 else |
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50 error ("convhull: first two input arguments must be vectors of same size"); |
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51 endif |
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52 |
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53 n = rows (i); |
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54 i = i'(:); |
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55 H = zeros (n + 1, 1); |
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56 |
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57 H(1) = i(1); |
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58 next_i = i(2); |
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59 i(2) = 0; |
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60 for k = 2:n |
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61 next_idx = find (i == next_i); |
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62 |
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63 if (rem (next_idx, 2) == 0) |
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64 H(k) = i(next_idx); |
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65 next_i = i(next_idx - 1); |
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66 i(next_idx - 1) = 0; |
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67 else |
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68 H(k) = i(next_idx); |
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69 next_i = i(next_idx + 1); |
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70 i(next_idx + 1) = 0; |
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71 endif |
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72 endfor |
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73 |
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74 H(n + 1) = H(1); |
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75 endfunction |
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76 |
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77 %!test |
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78 %! x = -3:0.5:3; |
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79 %! y = abs (sin (x)); |
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80 %! assert (convhull (x, y, {"s","Qci","Tcv","Pp"}), [1;7;13;12;11;10;4;3;2;1]) |
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81 |
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82 %!demo |
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83 %! x = -3:0.05:3; |
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84 %! y = abs (sin (x)); |
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85 %! k = convhull (x, y); |
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86 %! plot (x(k),y(k),'r-',x,y,'b+'); |
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87 %! axis ([-3.05, 3.05, -0.05, 1.05]); |
