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function h=ndgaussian(r, sigma, ndim)
%
% h=ndgaussian(r, sigma, ndim)
%
% create an ND Gaussian or box filter kernel matrix
%
% author: Qianqian Fang (q.fang at neu.edu)
%
% input:
%    r: kernel half-width, the output is 2*r+1 in each dimension; if
%       missing, use 1
%    sigma: the standard deviation of the Gaussian; if not given, use 1; if
%       set to inf, output box filter
%    ndim: an integer for the output dimension; if not given, use 3
%
% output:
%    h: an ndim-dimensional matrix
%
% -- this function is part of the Iso2Mesh Toolbox (http://iso2mesh.sf.net)
%    License: GPL v3 or later, see LICENSE.txt for details
%

if(nargin<3)
    ndim=3;
    if(nargin<2)
        sigma=1;
        if(nargin==0)
            r=1;
        end
    end
end
latt=cell(ndim,1);
if(isinf(sigma)) % ND box filter
    if(ndim==1)
         h=ones(1,(2*r+1));
    else
         h=ones((2*r+1)*ones(1,ndim));
    end
    return;
end
[latt{:}]=meshgrid(-r:r);
latt=cellfun(@(x) x.*x, latt,'uniformoutput',false);
h=exp(-(sum(cat(ndims(latt{1})+1,latt{:}),ndims(latt{1})+1))./(2*sigma*sigma));
h=h./(sum(h(:)));