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+## Copyright (C) 2007  David Bateman  <dbateman@free.fr>
+##
+## 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 2, 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, write to the Free
+## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+## 02110-1301, USA.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{yi} =} griddatan (@var{x}, @var{y}, @var{xi}, @var{method}, @var{options})
+## 
+## Generate a regular mesh from irregular data using interpolation.
+## The function is defined by @code{@var{y} = f (@var{x})}.
+## The interpolation points are all @var{xi}.  
+##
+## The interpolation method can be 'nearest' or 'linear'. If method is 
+## omitted it defaults to 'linear'.
+## @seealso{griddata, delaunayn}
+## @end deftypefn
+
+function [yi] = griddatan (x,y,xi,method,varargin)
+	
+  if (nargin == 3)
+    method="linear";
+  endif
+  if (nargin < 3) 
+    print_usage();
+  endif
+
+  if (ischar(method))
+    method=tolower(method);
+  endif
+
+  [m, n] = size(x);
+  [mi, ni] = size(xi);
+  
+  if (n != ni || size(y,1) != m || size(y,2) != 1)
+    error ("griddatan: dimensional mismatch");
+  endif
+
+  ## triangulate data
+  ## tri = delaunayn(x, varargin{:});
+  tri = delaunayn(x);
+
+  yi = nan(mi, 1);
+  
+  if strcmp(method,'nearest')
+    ## search index of nearest point
+    idx = dsearchn(x,tri,xi);
+    valid = !isnan(idx);
+    yi(valid) = y(idx(valid));
+
+  elseif strcmp(method,'linear')
+    ## search for every point the enclosing triangle
+    [tri_list, bary_list] = tsearchn(x,tri,xi);
+
+    ## only keep the points within triangles.
+    valid = !isnan(tri_list);
+    tri_list = tri_list(!isnan(tri_list));
+    bary_list = bary_list(!isnan(tri_list), :);
+    nr_t = rows(tri_list);
+
+    ## assign x,y for each point of simplex
+    xt =  reshape (x(tri(tri_list,:),:),[nr_t, n+1, n]);
+    yt = y(tri(tri_list,:));
+
+    ## Use barycentric coordinate of point to calculate yi
+    yi(valid) = sum (y(tri(tri_list,:)) .* bary_list, 2);
+
+  else
+    method
+    error("griddatan: unknown interpolation method");
+  endif
+
+endfunction
+
+%!test
+%! [xx,yy] = meshgrid(linspace(-1,1,32));
+%! xi = [xx(:), yy(:)];
+%! x = (2 * rand(100,2) - 1);
+%! x = [x;1,1;1,-1;-1,-1;-1,1];
+%! y = sin(2*(sum(x.^2,2)));
+%! zz = griddatan(x,y,xi,'linear');
+%! zz2 = griddata(x(:,1),x(:,2),y,xi(:,1),xi(:,2),'linear');
+%! assert (zz, zz2, 1e-10)
+
+%!test
+%! [xx,yy] = meshgrid(linspace(-1,1,32));
+%! xi = [xx(:), yy(:)];
+%! x = (2 * rand(100,2) - 1);
+%! x = [x;1,1;1,-1;-1,-1;-1,1];
+%! y = sin(2*(sum(x.^2,2)));
+%! zz = griddatan(x,y,xi,'nearest');
+%! zz2 = griddata(x(:,1),x(:,2),y,xi(:,1),xi(:,2),'nearest');
+%! assert (zz, zz2, 1e-10)