diff toolboxes/distance_learning/mlr/metricPsi/metricPsiPO.m @ 0:e9a9cd732c1e tip

first hg version after svn

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolboxes/distance_learning/mlr/metricPsi/metricPsiPO.m	Tue Feb 10 15:05:51 2015 +0000
@@ -0,0 +1,25 @@
+function S = metricPsiPO(q, y, n, pos, neg)
+%
+%   S = metricPsiPO(q, y, n, d, pos, neg)
+%
+%   q   = index of the query point
+%   y   = the ordering to compute
+%   n   = number of points in the data set
+%   pos = indices of relevant results for q
+%   neg = indices of irrelevant results for q
+%
+%   S is the vector of weights for q
+
+    yp          = ismember(y, pos);
+    NumPOS      = sum(yp);
+    PosAfter    = NumPOS - cumsum(yp);
+
+    yn          = ~yp;
+    NumNEG      = sum(yn);
+    NegBefore   = cumsum(yn) - yn;
+
+    S = zeros(n,1);
+
+    S(y)    = 2 * (yp .* NegBefore - yn .* PosAfter) / (NumNEG * NumPOS);
+
+end