[io] Add a gridcreator for subgrids

* expects a host grid and an element selector
* returns a unique_ptr to the subgrid

dumux/io/subgridgridcreator.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*****************************************************************************
+ *   See the file COPYING for full copying permissions.                      *
+ *                                                                           *
+ *   This program is free software: you can redistribute it and/or modify    *
+ *   it under the terms of the GNU General Public License as published by    *
+ *   the Free Software Foundation, either version 2 of the License, or       *
+ *   (at your option) any later version.                                     *
+ *                                                                           *
+ *   This program is distributed in the hope that it will be useful,         *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of          *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the            *
+ *   GNU General Public License for more details.                            *
+ *                                                                           *
+ *   You should have received a copy of the GNU General Public License       *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>.   *
+ *****************************************************************************/
+/*!
+ * \file
+ * \brief  A grid creator for dune-subgrid.
+ */
+#ifndef DUMUX_SUBGRID_GRID_CREATOR_HH
+#define DUMUX_SUBGRID_GRID_CREATOR_HH
+
+#if HAVE_DUNE_SUBGRID
+
+#include <memory>
+
+#include <dune/subgrid/subgrid.hh>
+#include <dune/grid/io/file/vtk.hh>
+#include <dune/grid/io/file/dgfparser/dgfwriter.hh>
+
+#include <dumux/common/parameters.hh>
+
+namespace Dumux {
+
+/*!
+ * \brief A grid creator for dune-subgrid.
+ */
+template <class HostGrid>
+class SubgridGridCreator
+{
+    static constexpr auto dim = HostGrid::dimension;
+
+public:
+    using Grid = Dune::SubGrid<dim, HostGrid>;
+
+    /*!
+     * \brief Make the subgrid.
+     */
+    template<class ElementSelector>
+    static std::unique_ptr<Grid> makeGrid(HostGrid& hostgrid,
+                                          const ElementSelector& selector,
+                                          const std::string& modelParamGroup = "")
+    {
+        // A unique pointer to the subgrid.
+        auto subgridPtr = std::make_unique<Grid>(hostgrid);
+
+        // A container to store the host grid elements' ids.
+        std::set<typename HostGrid::Traits::GlobalIdSet::IdType> elementsForSubgrid;
+        const auto& globalIDset = subgridPtr->getHostGrid().globalIdSet();
+
+        // Construct the subgrid.
+        subgridPtr->createBegin();
+
+        // Loop over all elements of the host grid and use the selector to
+        // choose which elements to add to the subgrid.
+        auto hostGridView = subgridPtr->getHostGrid().leafGridView();
+        for (const auto& e : elements(hostGridView))
+            if(selector(e))
+                elementsForSubgrid.insert(globalIDset.template id<0>(e));
+
+        subgridPtr->insertSetPartial(elementsForSubgrid);
+        subgridPtr->createEnd();
+
+        // If desired, write out the final subgrid as a dgf file.
+        if(getParamFromGroup<bool>(modelParamGroup, "Grid.WriteSubGridToDGF", false))
+        {
+            const auto postfix = getParamFromGroup<std::string>(modelParamGroup, "Problem.Name", "");
+            const std::string name = postfix == "" ? "subgrid" : "subgrid_" + postfix;
+            Dune::DGFWriter<typename Grid::LeafGridView> writer(subgridPtr->leafGridView());
+            writer.write(name + ".dgf");
+        }
+
+        // If desired, write out the hostgrid as vtk file.
+        if(getParamFromGroup<bool>(modelParamGroup, "Grid.WriteSubGridToVtk", false))
+        {
+            const auto postfix = getParamFromGroup<std::string>(modelParamGroup, "Problem.Name", "");
+            const std::string name = postfix == "" ? "subgrid" : "subgrid_" + postfix;
+            Dune::VTKWriter<typename Grid::LeafGridView> vtkWriter(subgridPtr->leafGridView());
+            vtkWriter.write(name);
+        }
+
+        // Return a unique pointer to the subgrid.
+        return subgridPtr;
+    }
+};
+
+} // end namespace Dumux
+
+#endif // HAVE_DUNE_SUBGRID
+#endif // DUMUX_SUBGRID_GRID_CREATOR_HH