New constructor version for PETScSparseMatrix

The new variant allows to pass a function object in place of a
PrimitiveStorage object to be used for determination of DoF counts.

Testing new approach in PetscMatrixAssemblyTest.

src/hyteg/petsc/PETScSparseMatrix.hpp

@@ -51,7 +51,8 @@ class PETScSparseMatrix
                       uint_t          globalSize,
                       const char      name[]            = "Mat",
                       const MPI_Comm& petscCommunicator = walberla::mpi::MPIManager::instance()->comm() )
-   : petscCommunicator_( petscCommunicator ), assembled_( false )
+   : petscCommunicator_( petscCommunicator )
+   , assembled_( false )
    {
       MatCreate( petscCommunicator, &mat );
       MatSetType( mat, MATMPIAIJ );
@@ -72,6 +73,16 @@ class PETScSparseMatrix
                         petscCommunicator )
    {}
 
+   PETScSparseMatrix( const FunctionType< PetscInt >& enumerator,
+                      const uint_t&                   level,
+                      const char                      name[]            = "Mat",
+                      const MPI_Comm&                 petscCommunicator = walberla::mpi::MPIManager::instance()->comm() )
+   : PETScSparseMatrix( numberOfLocalDoFs( enumerator, level ),
+                        numberOfGlobalDoFs( enumerator, level, petscCommunicator ),
+                        name,
+                        petscCommunicator )
+   {}
+
    virtual ~PETScSparseMatrix() { MatDestroy( &mat ); }
 
    inline void createMatrixFromOperator( const OperatorType&             op,

tests/hyteg/Petsc/PetscMatrixAssemblyTest.cpp

@@ -85,12 +85,12 @@ void testAssembly_newAPI( std::shared_ptr< PrimitiveStorage >& storage, uint_t l
 {
    WALBERLA_LOG_INFO_ON_ROOT( " * " << tag );
 
-   PETScManager                                                            petscManager;
-   PETScSparseMatrix< operType, operType::srcType::template FunctionType > matrix( storage, level, tag.c_str() );
-
    typename operType::srcType::template FunctionType< PetscInt > enumerator( "enumerator", storage, level, level );
    enumerator.enumerate( level );
 
+   PETScManager                                                            petscManager;
+   PETScSparseMatrix< operType, operType::srcType::template FunctionType > matrix( enumerator, level, tag.c_str() );
+
    operType oper( storage, level, level );
    matrix.createMatrixFromOperator_newAPI( oper, level, enumerator, All );
 }