function [n2, n] = dist2_radians(x, c)
%DIST2_RADIANS	Calculates squared distance between two sets of points.
%
%  We had to modify DIST2 a bit to cope with the circular nature of
%  angular space
%
%	Description
%	D = DIST2_RADIANS(X, C) takes two matrices of vectors and calculates the
%	squared Euclidean distance between them.  Both matrices must be of
%	 dimension 1.  If X has M rows and 1 column, and C has
%	L rows and 1 column, then the result has M rows and L columns.  The
%	I, Jth entry is the  squared distance from the Ith row of X to the
%	Jth row of C.
%
%	See also
%	GMMACTIV, KMEANS, RBFFWD
%

%	Copyright (c) Ian T Nabney (1996-2001)

siz = size(x);
if sum( siz > 1 ) > 1
  error('"x" dimension must be one' );
end
x = x(:);
ndata = length( x );

siz = size(c);
if sum( siz > 1 ) > 1
  error('"c" dimension must be one' );
end
c = c(:);
ncentres = length( c );

n  = repmat( NaN, ndata, ncentres );
n2 = repmat( NaN, ndata, ncentres );

for ic = 1:ncentres
  
  % Centre data around this centre
  n( :, ic ) = - pi + mod( x - c( ic ) + pi, 2 * pi );

end

n2 = n .^ 2;

% Rounding errors occasionally cause negative entries in n2
if any(any(n2<0))
  n2(n2<0) = 0;
end