function K = rbf4nn_vecss( X, Y, sigsq )
%function K = rbf4_vecss( X, Y, sigsq )
%
% Computes an rbf kernel matrix of X with Y, using a diagonal
% covariance matrix specified in sigsq.  Sigsq is specified as
% a column vector.
%
%INPUTS
% X = a matrix containing all samples as columns.
% Y = another matrix containing samples as columns.
% sigsq = column vector specifying the diagonal of the shape matrix.
%
%NOTE: the result does not include the normalization factor!
%
%OUTPUTS
% K_ij = exp(-1/(2*sigsq)*(X_i' * inv(diag(sigsq)) * Y_j))
%
% Adapted by D. Wingate from code written by Tijl De Bie.

sigsq = 1 ./ sigsq;

Xs = X.*X .* repmat( sigsq, 1, size(X,2) );
Xs = sum( Xs, 1 );

Ys = Y.*Y .* repmat( sigsq, 1, size(Y,2) );
Ys = sum( Ys, 1 );

Xt = Xs' * ones(1,length(Ys));
Yt = ones(length(Xs),1) * Ys;

p = X'*(repmat(sigsq,1,size(Y,2)).*Y);

K = exp( p + -0.5*( Xt + Yt ) );