fixed an issue with getSubmatrix

Former-commit-id: f4f8fb2f61

src/storage/SparseMatrix.cpp

@@ -525,7 +525,25 @@ namespace storm {
                     *it = i;
                 }
                 auto res = getSubmatrix(rowConstraint, columnConstraint, fakeRowGroupIndices, insertDiagonalElements);
-                res.rowGroupIndices = this->rowGroupIndices;
+
+                // Create a new row grouping that reflects the new sizes of the row groups.
+                std::vector<uint_fast64_t> newRowGroupIndices;
+                newRowGroupIndices.push_back(0);
+                auto selectedRowIt = rowConstraint.begin();
+
+                // For this, we need to count how many rows were preserved in every group.
+                for (uint_fast64_t group = 0; group < this->getRowGroupCount(); ++group) {
+                    uint_fast64_t newRowCount = 0;
+                    while (*selectedRowIt < this->getRowGroupIndices()[group + 1]) {
+                        ++selectedRowIt;
+                        ++newRowCount;
+                    }
+                    if (newRowCount > 0) {
+                        newRowGroupIndices.push_back(newRowGroupIndices.back() + newRowCount);
+                    }
+                }
+                
+                res.rowGroupIndices = newRowGroupIndices;
                 return res;
             }
         }
@@ -641,8 +659,6 @@ namespace storm {
             SparseMatrix<ValueType> res(getSubmatrix(false, rowsToKeep, storm::storage::BitVector(getColumnCount(), true), false));
             assert(res.getRowCount() == rowsToKeep.getNumberOfSetBits());
             assert(res.getColumnCount() == getColumnCount());
-            std::cout << getRowGroupCount() << std::endl;
-            std::cout << res.getRowGroupCount() << std::endl;
             assert(getRowGroupCount() == res.getRowGroupCount());
             return res;
         }

src/storage/SparseMatrix.h

@@ -603,6 +603,9 @@ namespace storm {
              * set to one in the given bit vector.
              *
              * @param useGroups If set to true, the constraint for the rows is interpreted as selecting whole row groups.
+             * If it is not set, the row constraint is interpreted over the actual rows. Note that empty row groups will
+             * be dropped altogether. That is, if no row of a row group is selected *or* the row group is alread empty,
+             * the submatrix will not have this row group.
              * @param constraint A bit vector indicating which rows to keep.
              * @param columnConstraint A bit vector indicating which columns to keep.
              * @param insertDiagonalEntries If set to true, the resulting matrix will have zero entries in column i for