samer@4: function y = logabsdet(A)
samer@4: % logabsdet - logabsdet(X)=log(abs(det(X))) 
samer@4: %
samer@4: % logabsdet :: [[N,N]] -> nonneg.
samer@4: %
samer@4: % This is faster and more stable than using log(det(A)).
samer@4: % (Except when A is not positive definite, in which case
samer@4: % we fall back to computing det(A) the usual way.)
samer@4: 
samer@4: %  From Tom Minka's lightspeed toolbox
samer@4: %  Samer: added clause incase A not pos def.
samer@4: 
samer@4: % this only works for HERMITIAN POS DEF matrix.
samer@4: % y = 2*sum(log(diag(chol(A))));
samer@4: 
samer@4: [R,p]=chol(A*A');
samer@4: if p>0,
samer@4: 	fprintf('*** logabsdet warning: matrix is singular');
samer@4: 	y=-inf;
samer@4: else
samer@4: 	y = sum(log(full(diag(R))));
samer@4: end