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scripts/geometry/convhull.m

changeset 10289: 4b124317dc38
parent:ec0a13863eb7
author: John W. Eaton <jwe@octave.org>
date: Tue Feb 09 20:58:55 2010 -0500 (46 minutes ago)
permissions: -rw-r--r--
description: base_properties::set_children: account for hidden children 
     1## Copyright (C) 2000, 2007, 2008 Kai Habel

     2##

     3## This file is part of Octave.

     4##

     5## Octave is free software; you can redistribute it and/or modify it

     6## under the terms of the GNU General Public License as published by

     7## the Free Software Foundation; either version 3 of the License, or (at

     8## your option) any later version.

     9##

    10## Octave is distributed in the hope that it will be useful, but

    11## WITHOUT ANY WARRANTY; without even the implied warranty of

    12## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    13## General Public License for more details.

    14##

    15## You should have received a copy of the GNU General Public License

    16## along with Octave; see the file COPYING.  If not, see

    17## <http://www.gnu.org/licenses/>.

    18

    19## -*- texinfo -*-

    20## @deftypefn {Function File} {@var{H} =} convhull (@var{x}, @var{y})

    21## @deftypefnx {Function File} {@var{H} =} convhull (@var{x}, @var{y}, @var{opt})

    22## Returns the index vector to the points of the enclosing convex hull.  The

    23## data points are defined by the x and y vectors.

    24##

    25## A third optional argument, which must be a string, contains extra options

    26## passed to the underlying qhull command.  See the documentation for the 

    27## Qhull library for details.

    28##

    29## @seealso{delaunay, convhulln}

    30## @end deftypefn

    31

    32## Author: Kai Habel <kai.habel@gmx.de>

    33

    34function H = convhull (x, y, opt)

    35

    36  if (nargin != 2 && nargin != 3)

    37    print_usage ();

    38  endif

    39

    40  if (isvector (x) && isvector (y) && length (x) == length (y))

    41    if (nargin == 2)

    42      i = convhulln ([x(:), y(:)]);

    43    elseif (ischar (opt) || iscell (opt))

    44      i = convhulln ([x(:), y(:)], opt);

    45    else

    46      error ("convhull: third argument must be a string or cell array of strings");

    47    endif

    48  else

    49    error ("convhull: first two input arguments must be vectors of same size");

    50  endif

    51

    52  n = rows (i);

    53  i = i'(:);

    54  H = zeros (n + 1, 1);

    55

    56  H(1) = i(1);

    57  next_i = i(2);

    58  i(2) = 0;

    59  for k = 2:n

    60    next_idx = find (i == next_i);

    61

    62    if (rem (next_idx, 2) == 0)

    63      H(k) = i(next_idx);

    64      next_i = i(next_idx - 1);

    65      i(next_idx - 1) = 0;

    66    else

    67      H(k) = i(next_idx);

    68      next_i = i(next_idx + 1);

    69      i(next_idx + 1) = 0;

    70    endif

    71  endfor

    72

    73  H(n + 1) = H(1);

    74endfunction

    75

    76%!testif HAVE_QHULL

    77%! x = -3:0.5:3;

    78%! y = abs (sin (x));

    79%! assert (convhull (x, y, {"s","Qci","Tcv","Pp"}), [1;7;13;12;11;10;4;3;2;1])

    80

    81%!demo

    82%! x = -3:0.05:3;

    83%! y = abs (sin (x));

    84%! k = convhull (x, y);

    85%! plot (x(k),y(k),'r-',x,y,'b+');

    86%! axis ([-3.05, 3.05, -0.05, 1.05]);