some more cleanup

include/aspect/compat.h

@@ -57,7 +57,6 @@ namespace aspect
       check (const unsigned int step,
              const double check_value)
       {
-
         dealii::SolverControl::State return_value = dealii::SolverControl::check(step, check_value);
 
         if (history_data_enabled)

include/aspect/global.h

@@ -302,6 +302,11 @@ namespace aspect
      */
     typedef dealii::TrilinosWrappers::BlockSparseMatrix BlockSparseMatrix;
 
+    /**
+     * Typedef for the base class for all preconditioners.
+     */
+    typedef dealii::TrilinosWrappers::PreconditionBase PreconditionBase;
+
     /**
      * Typedef for the AMG preconditioner type used for the top left block of
      * the Stokes matrix.

include/aspect/melt.h

@@ -132,6 +132,15 @@ namespace aspect
          * Returns the cell-averaged and cut-off value of p_c_scale,
          * the factor we use to rescale the compaction pressure and to
          * decide if a cell is a melt cell.
+         * The last input argument consider_is_melt_cell determines if
+         * this computation takes into account if a cell is a "melt cell"
+         * (cells where we solve the melt transport equations, as
+         * indicated by the entries stored in the is_melt_cell vector of
+         * the melt handler) and return a value of zero if the cell is
+         * not a melt cell (if true), or whether the computation should
+         * disregard the information about which cells are melt cells,
+         * which is required when we want to update the is_melt_cell
+         * vector and find out which cells should be melt cells (if false).
          */
         double p_c_scale (const MaterialModel::MaterialModelInputs<dim> &inputs,
                           const MaterialModel::MaterialModelOutputs<dim> &outputs,
@@ -230,7 +239,6 @@ namespace aspect
         virtual
         std::vector<double>
         compute_residual(internal::Assembly::Scratch::ScratchBase<dim> &scratch) const;
-
     };
 
     /**
@@ -423,8 +431,11 @@ namespace aspect
 
     private:
       /**
-       * is_melt_cell_vector[cell->active_cell_index()] says whether we have
-       * melt transport in this cell or not.
+       * is_melt_cell_vector[cell->active_cell_index()] says whether we want to
+       * solve the melt transport equations (as opposed to the Stokes equations without
+       * melt) in this cell or not. The value is set to true or false based on the
+       * porosity in the cell (only cells where the porosity is above a threshold are
+       * considered melt cells).
        */
       std::vector<bool> is_melt_cell_vector;
 

include/aspect/particle/property/melt_particle.h

@@ -113,6 +113,23 @@ namespace aspect
           virtual
           std::vector<std::pair<std::string, unsigned int> >
           get_property_information() const;
+
+          /**
+           * Declare the parameters this class takes through input files.
+           */
+          static
+          void
+          declare_parameters (ParameterHandler &prm);
+
+          /**
+           * Read the parameters this class declares from the parameter file.
+           */
+          virtual
+          void
+          parse_parameters (ParameterHandler &prm);
+
+        private:
+          double threshold_for_melt_presence;
       };
     }
   }

include/aspect/simulator.h

@@ -1672,7 +1672,7 @@ namespace aspect
 
 
       std_cxx11::shared_ptr<LinearAlgebra::PreconditionAMG>     Amg_preconditioner;
-      std_cxx11::shared_ptr<LinearAlgebra::PreconditionAMG>     Mp_preconditioner;
+      std_cxx11::shared_ptr<LinearAlgebra::PreconditionBase>    Mp_preconditioner;
 
       bool                                                      rebuild_sparsity_and_matrices;
       bool                                                      rebuild_stokes_matrix;

include/aspect/simulator_access.h

@@ -707,6 +707,12 @@ namespace aspect
       bool
       pressure_rhs_needs_compatibility_modification() const;
 
+      /**
+       * Return whether the model uses a prescribed Stokes solution.
+       */
+      bool
+      model_has_prescribed_stokes_solution () const;
+
       /**
        * A convenience function that copies the values of the compositional
        * fields at the quadrature point q given as input parameter to the