Let the topological equation solvers handle singleton SCCs with self-loops directly.

src/storm/solver/TopologicalLinearEquationSolver.cpp

@@ -80,7 +80,7 @@ namespace storm {
             } else {
                 storm::storage::BitVector sccAsBitVector(x.size(), false);
                 for (auto const& scc : *this->sortedSccDecomposition) {
-                    if (scc.isTrivial()) {
+                    if (scc.size() == 1) {
                         returnValue = solveTrivialScc(*scc.begin(), x, b) && returnValue;
                     } else {
                         sccAsBitVector.clear();
@@ -131,8 +131,12 @@ namespace storm {
             }
             
             if (hasDiagonalEntry) {
+                    if (storm::utility::isZero(denominator)) {
+                        STORM_LOG_THROW(storm::utility::isZero(xi), storm::exceptions::InvalidOperationException, "The equation system has no solution.");
+                    } else {
                         xi /= denominator;
                     }
+            }
             return true;
         }
         

src/storm/solver/TopologicalMinMaxLinearEquationSolver.cpp

@@ -78,7 +78,7 @@ namespace storm {
                 storm::storage::BitVector sccRowGroupsAsBitVector(x.size(), false);
                 storm::storage::BitVector sccRowsAsBitVector(b.size(), false);
                 for (auto const& scc : *this->sortedSccDecomposition) {
-                    if (scc.isTrivial()) {
+                    if (scc.size() == 1) {
                         returnValue = solveTrivialScc(*scc.begin(), dir, x, b) && returnValue;
                     } else {
                         sccRowGroupsAsBitVector.clear();
@@ -142,8 +142,18 @@ namespace storm {
                     }
                 }
                 if (hasDiagonalEntry) {
+                    if (storm::utility::isZero(denominator)) {
+                        if (!storm::utility::isZero(rowValue)) {
+                            if (rowValue > storm::utility::zero<ValueType>()) {
+                                rowValue = storm::utility::infinity<ValueType>();
+                            } else {
+                                rowValue = -storm::utility::infinity<ValueType>();
+                            }
+                        }
+                    } else {
                         rowValue /= denominator;
                     }
+                }
                 if (firstRow) {
                     xi = std::move(rowValue);
                     bestRow = row;