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## Copyright (C) 2007-2013 David Bateman
##
## 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
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{vi} =} interp3 (@var{x}, @var{y}, @var{z}, @var{v}, @var{xi}, @var{yi}, @var{zi})
## @deftypefnx {Function File} {@var{vi} =} interp3 (@var{v}, @var{xi}, @var{yi}, @var{zi})
## @deftypefnx {Function File} {@var{vi} =} interp3 (@var{v}, @var{m})
## @deftypefnx {Function File} {@var{vi} =} interp3 (@var{v})
## @deftypefnx {Function File} {@var{vi} =} interp3 (@dots{}, @var{method})
## @deftypefnx {Function File} {@var{vi} =} interp3 (@dots{}, @var{method}, @var{extrapval})
##
## Perform 3-dimensional interpolation. Each element of the 3-dimensional
## array @var{v} represents a value at a location given by the parameters
## @var{x}, @var{y}, and @var{z}. The parameters @var{x}, @var{x}, and
## @var{z} are either 3-dimensional arrays of the same size as the array
## @var{v} in the @qcode{"meshgrid"} format or vectors. The parameters
## @var{xi}, etc. respect a similar format to @var{x}, etc., and they
## represent the points at which the array @var{vi} is interpolated.
##
## If @var{x}, @var{y}, @var{z} are omitted, they are assumed to be
## @code{x = 1 : size (@var{v}, 2)}, @code{y = 1 : size (@var{v}, 1)} and
## @code{z = 1 : size (@var{v}, 3)}. If @var{m} is specified, then
## the interpolation adds a point half way between each of the interpolation
## points. This process is performed @var{m} times. If only @var{v} is
## specified, then @var{m} is assumed to be @code{1}.
##
## Method is one of:
##
## @table @asis
## @item @qcode{"nearest"}
## Return the nearest neighbor.
##
## @item @qcode{"linear"}
## Linear interpolation from nearest neighbors.
##
## @item @qcode{"cubic"}
## Cubic interpolation from four nearest neighbors (not implemented yet).
##
## @item @qcode{"spline"}
## Cubic spline interpolation---smooth first and second derivatives
## throughout the curve.
## @end table
##
## The default method is @qcode{"linear"}.
##
## If @var{extrap} is the string @qcode{"extrap"}, then extrapolate values
## beyond the endpoints. If @var{extrap} is a number, replace values beyond
## the endpoints with that number. If @var{extrap} is missing, assume NA.
## @seealso{interp1, interp2, spline, meshgrid}
## @end deftypefn
function vi = interp3 (varargin)
method = "linear";
extrapval = NA;
nargs = nargin;
if (nargin < 1 || ! isnumeric (varargin{1}))
print_usage ();
endif
if (ischar (varargin{end}))
method = varargin{end};
nargs = nargs - 1;
elseif (nargs > 1 && ischar (varargin{end - 1}))
if (! isnumeric (varargin{end}) || ! isscalar (varargin{end}))
error ("interp3: extrapal is expected to be a numeric scalar");
endif
extrapval = varargin{end};
method = varargin{end-1};
nargs = nargs - 2;
endif
if (nargs < 3 || (nargs == 4 && ! isvector (varargin{1})
&& nargs == (ndims (varargin{1}) + 1)))
v = varargin{1};
if (ndims (v) != 3)
error ("interp3: expect 3-dimensional array of values");
endif
x = varargin (2:nargs);
if (any (! cellfun (@isvector, x)))
for i = 2 : 3
if (! size_equal (x{1}, x{i}))
error ("interp3: dimensional mismatch");
endif
x{i} = permute (x{i}, [2, 1, 3]);
endfor
x{1} = permute (x{1}, [2, 1, 3]);
endif
v = permute (v, [2, 1, 3]);
vi = ipermute (interpn (v, x{:}, method, extrapval), [2, 1, 3]);
elseif (nargs == 7 && nargs == (2 * ndims (varargin{ceil (nargs / 2)})) + 1)
v = varargin{4};
if (ndims (v) != 3)
error ("interp3: expect 3-dimensional array of values");
endif
x = varargin (1:3);
if (any (! cellfun (@isvector, x)))
for i = 2 : 3
if (! size_equal (x{1}, x{i}) || ! size_equal (x{i}, v))
error ("interp3: dimensional mismatch");
endif
x{i} = permute (x{i}, [2, 1, 3]);
endfor
x{1} = permute (x{1}, [2, 1, 3]);
endif
y = varargin (5:7);
if (any (! cellfun (@isvector, y)))
for i = 2 : 3
if (! size_equal (y{1}, y{i}))
error ("interp3: dimensional mismatch");
endif
y{i} = permute (y{i}, [2, 1, 3]);
endfor
y{1} = permute (y{1}, [2, 1, 3]);
endif
v = permute (v, [2, 1, 3]);
vi = ipermute (interpn (x{:}, v, y{:}, method, extrapval), [2, 1, 3]);
else
error ("interp3: wrong number or incorrectly formatted input arguments");
endif
endfunction
%!test
%! x = y = z = -1:1; y = y + 2;
%! f = @(x,y,z) x.^2 - y - z.^2;
%! [xx, yy, zz] = meshgrid (x, y, z);
%! v = f (xx,yy,zz);
%! xi = yi = zi = -1:0.5:1; yi = yi + 2.1;
%! [xxi, yyi, zzi] = meshgrid (xi, yi, zi);
%! vi = interp3 (x, y, z, v, xxi, yyi, zzi);
%! [xxi, yyi, zzi] = ndgrid (yi, xi, zi);
%! vi2 = interpn (y, x, z, v, xxi, yyi, zzi);
%! tol = 10 * eps;
%! assert (vi, vi2, tol);
%!test
%! x=z=1:2; y=1:3;xi=zi=.6:1.6; yi=1; v=ones([3,2,2]); v(:,2,1)=[7 ;5;4]; v(:,1,2)=[2 ;3;5];
%! [xxi3, yyi3, zzi3] = meshgrid (xi, yi, zi);
%! [xxi, yyi, zzi] = ndgrid (yi, xi, zi);
%! vi = interp3 (x, y, z, v, xxi3, yyi3, zzi3, "nearest");
%! vi2 = interpn (y, x, z, v, xxi, yyi, zzi,"nearest");
%! assert (vi, vi2);
%!test
%! x=z=1:2; y=1:3;xi=zi=.6:1.6; yi=1; v=ones([3,2,2]); v(:,2,1)=[7 ;5;4]; v(:,1,2)=[2 ;3;5];
%! vi = interp3 (x, y, z, v, xi+1, yi, zi, "nearest",3);
%! vi2 = interpn (y, x, z, v, yi, xi+1, zi,"nearest", 3);
%! assert (vi, vi2);
%!test
%! x=z=1:2; y=1:3;xi=zi=.6:1.6; yi=1; v=ones([3,2,2]); v(:,2,1)=[7 ;5;4]; v(:,1,2)=[2 ;3;5];
%! vi = interp3 (x, y, z, v, xi, yi, zi, "nearest");
%! vi2 = interpn (y, x, z, v, yi, xi, zi,"nearest");
%! assert (vi, vi2);
%!test
%! x=z=1:2; y=1:3;xi=zi=.6:1.6; yi=1; v=ones([3,2,2]); v(:,2,1)=[7 ;5;4]; v(:,1,2)=[2 ;3;5];
%! vi = interp3 (v, xi, yi, zi, "nearest",3);
%! vi2 = interpn (v, yi, xi, zi,"nearest", 3);
%! assert (vi, vi2);
%!test
%! xi=zi=.6:1.6; yi=1; v=ones([3,2,2]); v(:,2,1)=[7 ;5;4]; v(:,1,2)=[2 ;3;5];
%! vi = interp3 (v, xi, yi, zi, "nearest");
%! vi2 = interpn (v, yi, xi, zi,"nearest");
%! assert (vi, vi2);
%!shared z, zout, tol
%! z = zeros (3, 3, 3);
%! zout = zeros (5, 5, 5);
%! z(:,:,1) = [1 3 5; 3 5 7; 5 7 9];
%! z(:,:,2) = z(:,:,1) + 2;
%! z(:,:,3) = z(:,:,2) + 2;
%! for n = 1:5
%! zout(:,:,n) = [1 2 3 4 5;
%! 2 3 4 5 6;
%! 3 4 5 6 7;
%! 4 5 6 7 8;
%! 5 6 7 8 9] + (n-1);
%! end
%! tol = 10 * eps;
%!assert (interp3 (z), zout, tol)
%!assert (interp3 (z, "linear"), zout, tol)
%!assert (interp3 (z, "spline"), zout, tol)
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