From fb7fe6a8e18f325f4f8e61c5899363f93e9edcc6 Mon Sep 17 00:00:00 2001
From: Wenzel Jakob <wenzel@cs.cornell.edu>
Date: Thu, 15 Nov 2012 00:52:14 -0500
Subject: [PATCH] prevent excessive MLT/ERPT error messages due to roundoff
 errors

---
 src/integrators/erpt/erpt_proc.cpp | 16 +++++++++-------
 src/integrators/mlt/mlt_proc.cpp   |  4 +++-
 src/libbidir/mut_manifold.cpp      |  5 ++++-
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/integrators/erpt/erpt_proc.cpp b/src/integrators/erpt/erpt_proc.cpp
index 13708297..fe5b7714 100644
--- a/src/integrators/erpt/erpt_proc.cpp
+++ b/src/integrators/erpt/erpt_proc.cpp
@@ -234,15 +234,17 @@ public:
 						}
 					#endif
 
-					#if defined(MTS_BD_DEBUG)
-					if (Qxy <= 0 || Qyx < 0 || std::isnan(Qxy) || std::isnan(Qyx)) {
-						Log(EDebug, "Source path: %s", current->toString().c_str());
-						Log(EDebug, "Proposal path: %s", proposed->toString().c_str());
-						Log(EWarn, "Internal error while computing acceptance probabilities: "
-							"Qxy=%f, Qyx=%f, muRec=%s", Qxy, Qyx, muRec.toString().c_str());
+					if (Qxy == 0) { // be tolerant of this (can occasionally happen due to floating point inaccuracies)
+						a = 0;
+					} else if (Qxy < 0 || Qyx < 0 || std::isnan(Qxy) || std::isnan(Qyx)) {
+						#if defined(MTS_BD_DEBUG)
+							Log(EDebug, "Source path: %s", current->toString().c_str());
+							Log(EDebug, "Proposal path: %s", proposed->toString().c_str());
+							Log(EWarn, "Internal error while computing acceptance probabilities: "
+								"Qxy=%f, Qyx=%f, muRec=%s", Qxy, Qyx, muRec.toString().c_str());
+						#endif
 						a = 0;
 					}
-					#endif
 
 					accumulatedWeight += 1-a;
 
diff --git a/src/integrators/mlt/mlt_proc.cpp b/src/integrators/mlt/mlt_proc.cpp
index d70132e0..7d820505 100644
--- a/src/integrators/mlt/mlt_proc.cpp
+++ b/src/integrators/mlt/mlt_proc.cpp
@@ -235,7 +235,9 @@ public:
 					}
 				#endif
 
-				if (Qxy <= 0 || Qyx < 0 || std::isnan(Qxy) || std::isnan(Qyx)) {
+				if (Qxy == 0) { // be tolerant of this (can occasionally happen due to floating point inaccuracies)
+					a = 0;
+				} else if (Qxy < 0 || Qyx < 0 || std::isnan(Qxy) || std::isnan(Qyx)) {
 					#if defined(MTS_BD_DEBUG)
 						Log(EDebug, "Source path: %s", current->toString().c_str());
 						Log(EDebug, "Proposal path: %s", proposed->toString().c_str());
diff --git a/src/libbidir/mut_manifold.cpp b/src/libbidir/mut_manifold.cpp
index 7d589c04..5835456f 100644
--- a/src/libbidir/mut_manifold.cpp
+++ b/src/libbidir/mut_manifold.cpp
@@ -272,7 +272,6 @@ bool ManifoldPerturbation::sampleMutation(
 	for (int i=l+1; i<m; ++i) {
 		proposal.append(m_pool.allocVertex());
 		proposal.append(m_pool.allocEdge());
-		memset(proposal.vertex(proposal.vertexCount()-1), 0, sizeof(PathVertex)); /// XXX
 	}
 	proposal.append(source, m, k+1);
 
@@ -665,6 +664,10 @@ Float ManifoldPerturbation::Q(const Path &source, const Path &proposal,
 		if (prob == 0)
 			return 0.0f;
 		weight /= prob;
+
+		/* Catch very low probabilities which round to +inf in the above division operation */
+		if (!std::isfinite(weight.average()))
+			return 0.0f;
 	} else {
 		Frame frame(source.vertex(a+step)->getGeometricNormal());