function out=entropy(pos,neg)
% information content / entropy
% always does normalization, hence works with integers or reals

sum=(pos+neg);
p1=pos./(pos+neg);
p2=neg./(pos+neg);
out=-p1.*log2(p1)-p2.*log2(p2);
% do some special processing to take care of 0*log2(0)
out=min(out,isfinite(out));