function [C,N,c] = conv2nan(X,Y,arg3);
% CONV2 2-dimensional convolution 
% X and Y can contain missing values encoded with NaN.
% NaN's are skipped, NaN do not result in a NaN output. 
% The output gives NaN only if there are insufficient input data
%
% [...] = CONV2NAN(X,Y);
%      calculates 2-dim convolution between X and Y
% [C]   = CONV2NAN(X,Y);

%    This function is part of the NaN-toolbox
%    http://www.dpmi.tu-graz.ac.at/~schloegl/matlab/NaN/
%

%	$Revision: 1.3 $
%	$Id: conv2nan.m,v 1.3 2005/05/25 13:02:04 schloegl Exp $
%	Copyright (C) 2000-2005 by Alois Schloegl <a.schloegl@ieee.org>	

%    This program 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 of the License, or
%    (at your option) any later version.
%
%    This program 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 this program; if not, write to the Free Software
%    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


if nargin~=2,
        fprintf(2,'Error CONV2NAN: incorrect number of input arguments\n');
end;

m = isnan(X);
n = isnan(Y);

X(m) = 0;
Y(n) = 0;

C = conv2(X,Y);         % 2-dim convolution
N = conv2(real(~m),real(~n));     % normalization term
c = conv2(ones(size(X)),ones(size(Y))); % correction of normalization

if nargout==1,
        C = C.*c./N;
elseif nargout==2,
        N = N./c;
end;