Daniel@0: function S = metricPsiPO(q, y, n, pos, neg)
Daniel@0: %
Daniel@0: %   S = metricPsiPO(q, y, n, d, pos, neg)
Daniel@0: %
Daniel@0: %   q   = index of the query point
Daniel@0: %   y   = the ordering to compute
Daniel@0: %   n   = number of points in the data set
Daniel@0: %   pos = indices of relevant results for q
Daniel@0: %   neg = indices of irrelevant results for q
Daniel@0: %
Daniel@0: %   S is the vector of weights for q
Daniel@0: 
Daniel@0:     yp          = ismember(y, pos);
Daniel@0:     NumPOS      = sum(yp);
Daniel@0:     PosAfter    = NumPOS - cumsum(yp);
Daniel@0: 
Daniel@0:     yn          = ~yp;
Daniel@0:     NumNEG      = sum(yn);
Daniel@0:     NegBefore   = cumsum(yn) - yn;
Daniel@0: 
Daniel@0:     S = zeros(n,1);
Daniel@0: 
Daniel@0:     S(y)    = 2 * (yp .* NegBefore - yn .* PosAfter) / (NumNEG * NumPOS);
Daniel@0: 
Daniel@0: end