[ML] Impose a cutoff on the minimum variance.

To avoid overflow when calculating lgamma values an absolute cutoff on the minimum variance must be set.

Fixes #488

Author: tveasey

lib/maths/CXMeansOnline1d.cc

@@ -295,7 +295,8 @@ void BICGain(maths_t::EDataType dataType,
     double a = pow2(m + gammaOffset) / v;
     double b = (m + gammaOffset) / v;
 
-    double vmin = std::min(MIN_RELATIVE_VARIANCE * v, MIN_ABSOLUTE_VARIANCE);
+    double smin = std::max(logNormalOffset, gammaOffset);
+    double vmin = std::min(MIN_RELATIVE_VARIANCE * std::max(v, pow2(smin)), MIN_ABSOLUTE_VARIANCE);
 
     // Mixture of normals
     double wl = CBasicStatistics::count(mvl) / n;