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########################################################################
##
## Copyright (C) 2001-2024 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{y} =} filter2 (@var{b}, @var{x})
## @deftypefnx {} {@var{y} =} filter2 (@var{b}, @var{x}, @var{shape})
## Apply the 2-D FIR filter @var{b} to @var{x}.
##
## If the argument @var{shape} is specified, return an array of the desired
## shape. Possible values are:
##
## @table @asis
## @item @qcode{"full"}
## pad @var{x} with zeros on all sides before filtering.
##
## @item @qcode{"same"}
## unpadded @var{x} (default)
##
## @item @qcode{"valid"}
## trim @var{x} after filtering so edge effects are no included.
## @end table
##
## Note this is just a variation on convolution, with the parameters reversed
## and @var{b} rotated 180 degrees.
## @seealso{conv2}
## @end deftypefn
function y = filter2 (b, x, shape)
if (nargin < 2)
print_usage ();
endif
if (nargin < 3)
shape = "same";
endif
[nr, nc] = size (b);
y = conv2 (x, b(nr:-1:1, nc:-1:1), shape);
endfunction
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