Added the compute_mean_squared_distance() function.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403419

dlib/svm/feature_ranking.h

@@ -9,6 +9,7 @@
 #include "feature_ranking_abstract.h"
 #include "kcentroid.h"
 #include "../optimization.h"
+#include "../statistics.h"
 #include <iostream>
 
 namespace dlib
@@ -448,6 +449,28 @@ namespace dlib
                                                              true);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T,
+        typename alloc
+        >
+    double compute_mean_squared_distance (
+        const std::vector<T,alloc>& samples
+    )
+    {
+        running_stats<double> rs;
+        for (unsigned long i = 0; i < samples.size(); ++i)
+        {
+            for (unsigned long j = i+1; j < samples.size(); ++j)
+            {
+                rs.add(length_squared(samples[i] - samples[j]));
+            }
+        }
+
+        return rs.mean();
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/svm/feature_ranking_abstract.h

@@ -107,6 +107,23 @@ namespace dlib
               standard out during its processing.
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T,
+        typename alloc
+        >
+    double compute_mean_squared_distance (
+        const std::vector<T,alloc>& samples
+    );
+    /*!
+        requires
+            - for all valid i: is_vector(samples[i]) == true
+        ensures
+            - computes the average value of the squares of all the pairwise 
+              distances between every element of samples.  
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }