[GNUnet-SVN] r18284 - gnunet/src/nse

[gnunet]

Author: grothoff
Date: 2011-11-23 19:48:46 +0100 (Wed, 23 Nov 2011)
New Revision: 18284

Modified:
   gnunet/src/nse/gnunet-service-nse.c
Log:
fixing variance calculation - we calculate the average from the same 
distribution, so the degrees of freedom is n-1

Modified: gnunet/src/nse/gnunet-service-nse.c
===================================================================
--- gnunet/src/nse/gnunet-service-nse.c 2011-11-23 17:23:52 UTC (rev 18283)
+++ gnunet/src/nse/gnunet-service-nse.c 2011-11-23 18:48:46 UTC (rev 18284)
@@ -349,7 +349,7 @@
 
   for (i = 0; i < estimate_count; i++)
   {
-    int j;
+    unsigned int j;
 
     j = (estimate_index - i + HISTORY_SIZE) % HISTORY_SIZE;
     val = htonl (size_estimate_messages[j].matching_bits);
@@ -359,9 +359,9 @@
   if (0 != estimate_count)
   {
     mean = sum / estimate_count;
-    variance = (vsq - mean * sum) / estimate_count; // terrible for numerical 
stability...
+    variance = (vsq - mean * sum) / (estimate_count - 1.0); // terrible for 
numerical stability...
     GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "(%f - %f) / %u = %f\n", 
-      vsq, mean * sum, estimate_count, variance);
+      vsq, mean * sum, estimate_count - 1, variance);
 
   }
 #endif