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########################################################################
##
## Copyright (C) 2007-2022 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{idx} =} tsearchn (@var{x}, @var{t}, @var{xi})
## @deftypefnx {} {[@var{idx}, @var{p}] =} tsearchn (@var{x}, @var{t}, @var{xi})
## Search for the enclosing Delaunay convex hull.
##
## For @code{@var{t} = delaunayn (@var{x})}, finds the index in @var{t}
## containing the points @var{xi}. For points outside the convex hull,
## @var{idx} is NaN.
##
## If requested @code{tsearchn} also returns the Barycentric coordinates
## @var{p} of the enclosing triangles.
## @seealso{delaunay, delaunayn}
## @end deftypefn
function [idx, p] = tsearchn (x, t, xi)
if (nargin != 3)
print_usage ();
endif
nt = rows (t);
[m, n] = size (x);
mi = rows (xi);
idx = NaN (mi, 1);
p = NaN (mi, n + 1);
ni = [1:mi].';
for i = 1 : nt
## Only calculate the Barycentric coordinates for points that have not
## already been found in a triangle.
b = cart2bary (x (t (i, :), :), xi(ni,:));
## Our points xi are in the current triangle if
## (all (b >= 0) && all (b <= 1)). However as we impose that
## sum (b,2) == 1 we only need to test all(b>=0). Note need to add
## a small margin for rounding errors
intri = all (b >= -1e-12, 2);
idx(ni(intri)) = i;
p(ni(intri),:) = b(intri, :);
ni(intri) = [];
endfor
endfunction
function Beta = cart2bary (T, P)
## Conversion of Cartesian to Barycentric coordinates.
## Given a reference simplex in N dimensions represented by an
## N+1-by-N matrix, an arbitrary point P in Cartesian coordinates,
## represented by an N-by-1 column vector can be written as
##
## P = Beta * T
##
## Where Beta is an N+1 vector of the barycentric coordinates. A criteria
## on Beta is that
##
## sum (Beta) == 1
##
## and therefore we can write the above as
##
## P - T(end, :) = Beta(1:end-1) * (T(1:end-1,:) - ones (N,1) * T(end,:))
##
## and then we can solve for Beta as
##
## Beta(1:end-1) = (P - T(end,:)) / (T(1:end-1,:) - ones (N,1) * T(end,:))
## Beta(end) = sum (Beta)
##
## Note code below is generalized for multiple values of P, one per row.
[M, N] = size (P);
Beta = (P - ones (M,1) * T(end,:)) / (T(1:end-1,:) - ones (N,1) * T(end,:));
Beta (:,end+1) = 1 - sum (Beta, 2);
endfunction
%!shared x, tri
%! x = [-1,-1;-1,1;1,-1];
%! tri = [1, 2, 3];
%!test
%! [idx, p] = tsearchn (x,tri,[-1,-1]);
%! assert (idx, 1);
%! assert (p, [1,0,0], 1e-12);
%!test
%! [idx, p] = tsearchn (x,tri,[-1,1]);
%! assert (idx, 1);
%! assert (p, [0,1,0], 1e-12);
%!test
%! [idx, p] = tsearchn (x,tri,[1,-1]);
%! assert (idx, 1);
%! assert (p, [0,0,1], 1e-12);
%!test
%! [idx, p] = tsearchn (x,tri,[-1/3,-1/3]);
%! assert (idx, 1);
%! assert (p, [1/3,1/3,1/3], 1e-12);
%!test
%! [idx, p] = tsearchn (x,tri,[1,1]);
%! assert (idx, NaN);
%! assert (p, [NaN, NaN, NaN]);
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