Merge pull request #262 from bangerth/comments

Fix a bug.

Author: bangerth

include/sampleflow/producers/differential_evaluation_mh.impl.h

@@ -233,12 +233,14 @@ namespace SampleFlow
                   b_dist(0, n_chains - 3);
 
                   typename std::vector<OutputType>::size_type b = b_dist(rng);
+                  if (b >= std::min<typename std::vector<OutputType>::size_type>(a, chain))
+                    ++b;
                   if (b >= std::max(a, chain))
-                    b += 2;
-                  else if (b >= std::min<typename std::vector<OutputType>::size_type>(a, chain))
-                    b += 1;
+                    ++b;
                   const OutputType trial_b = current_samples[b];
 
+                  assert (a!=b);
+
                   // Combine trial a and trial b
                   const OutputType crossover_result = crossover(current_samples[chain], trial_a, trial_b);
                   trial_sample_and_ratio = propose_sample(crossover_result);

tests/differential_evaluation_mh_producer_01.output

@@ -1 +1 @@
-Mean value = 1.9881
+Mean value = 1.98196