Assert that we have n>=2 samples

av-variance.c

@@ -27,6 +27,7 @@ double sample_variance(double set[], int set_n) {
   }
 
   // Divide by (n-1), as this is *sample* variance (Bessel's correction).
+  assert(set_n>1);
   ss /= (set_n-1);
 
   return ss;