libmesh-dev 0.7.1-2ubuntu1 / usr / include / libmesh / mesh_base.h

// $Id: mesh_base.h 4402 2011-04-22 23:10:19Z roystgnr $

// The libMesh Finite Element Library.
// Copyright (C) 2002-2008 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner
  
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
  
// This library 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
// Lesser General Public License for more details.
  
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA



#ifndef __mesh_base_h__
#define __mesh_base_h__



// C++ Includes   -----------------------------------
#include <string>

// Local Includes -----------------------------------
#include "auto_ptr.h"
#include "dof_object.h" // for invalid_processor_id
#include "enum_elem_type.h"
#include "libmesh_common.h"
#include "multi_predicates.h"
#include "partitioner.h" // AutoPtr needs a real declaration
#include "point_locator_base.h"
#include "variant_filter_iterator.h"

namespace libMesh
{

// forward declarations
class Elem;
class Node;
class Point;
class BoundaryInfo;
class MeshData;



/**
 * This is the \p MeshBase class. This class provides all the data necessary
 * to describe a geometric entity.  It allows for the description of a
 * \p dim dimensional object that lives in \p LIBMESH_DIM-dimensional space.
 * \par
 * A mesh is made of nodes and elements, and this class provides data
 * structures to store and access both.  A mesh may be partitioned into a
 * number of subdomains, and this class provides that functionality.
 * Furthermore, this class provides functions for reading and writing a
 * mesh to disk in various formats.
 *
 * \author  Benjamin S. Kirk
 * \date    $Date: 2011-04-22 18:10:19 -0500 (Fri, 22 Apr 2011) $
 * \version $Revision: 4402 $
 */


// ------------------------------------------------------------
// MeshBase class definition
class MeshBase
{
public:

  /**
   * Constructor.  Takes \p dim, the dimension of the mesh.
   * The mesh dimension can be changed (and may automatically be
   * changed by mesh generation/loading) later.
   */
  MeshBase (unsigned int dim=1);
  
  /**
   * Copy-constructor.
   */
  MeshBase (const MeshBase& other_mesh);

  /**
   * Virtual "copy constructor"
   */
  virtual AutoPtr<MeshBase> clone() const = 0;

  /**
   * Destructor.
   */
  virtual ~MeshBase ();

  /**
   * This class holds the boundary information.  It can store nodes, edges,
   * and faces with a corresponding id that facilitates setting boundary
   * conditions.
   */
  AutoPtr<BoundaryInfo> boundary_info;

  /**
   * A partitioner to use at each prepare_for_use()
   */
  virtual AutoPtr<Partitioner> &partitioner() { return _partitioner; }
  
  /**
   * Deletes all the data that are currently stored.
   */
  virtual void clear ();
  
  /**
   * @returns \p true if the mesh has been prepared via a call
   * to \p prepare_for_use, \p false otherwise.
   */
  bool is_prepared () const
  { return _is_prepared; }
  
  /**
   * @returns \p true if all elements and nodes of the mesh
   * exist on the current processor, \p false otherwise
   */
  virtual bool is_serial () const 
  { return true; }
  
  /**
   * Gathers all elements and nodes of the mesh onto
   * every processor
   */
  virtual void allgather () {}
  
  /**
   * When supported, deletes all nonlocal elements of the mesh
   * except for "ghosts" which touch a local element, and deletes
   * all nodes which are not part of a local or ghost element
   */
  virtual void delete_remote_elements () {}
  
  /**
   * @returns the logical dimension of the mesh; i.e. the manifold
   * dimension of the elements in the mesh.  If we ever support
   * multi-dimensional meshes (e.g. hexes and quads in the same mesh)
   * then this will return the largest such dimension.
   */
  unsigned int mesh_dimension () const
  { return static_cast<unsigned int>(_dim); }
  
  /**
   * Resets the logical dimension of the mesh.
   */
  void set_mesh_dimension (unsigned int d)
  { _dim = d; }
  
  /**
   * Returns the spatial dimension of the mesh.  Note that this is
   * defined at compile time in the header \p libmesh_common.h.
   */
  unsigned int spatial_dimension () const
  { return static_cast<unsigned int>(LIBMESH_DIM); }
  
  /**
   * Returns the number of nodes in the mesh. This function and others must
   * be defined in derived classes since the MeshBase class has no specific
   * storage for nodes or elements.
   */
  virtual unsigned int n_nodes () const = 0; 

  /**
   * Returns the number of nodes on processor \p proc.
   */
  unsigned int n_nodes_on_proc (const unsigned int proc) const;

  /**
   * Returns the number of nodes on the local processor.
   */
  unsigned int n_local_nodes () const
  { return this->n_nodes_on_proc (libMesh::processor_id()); }

  /**
   * Returns the number of nodes owned by no processor.
   */
  unsigned int n_unpartitioned_nodes () const
  { return this->n_nodes_on_proc (DofObject::invalid_processor_id); }

  /**
   * Returns a number greater than or equal to the maximum node id in the
   * mesh.
   */
  virtual unsigned int max_node_id () const = 0;

  /**
   * Reserves space for a known number of nodes.
   * Note that this method may or may not do anything, depending
   * on the actual \p Mesh implementation.  If you know the number
   * of nodes you will add and call this method before repeatedly
   * calling \p add_point() the implementation will be more efficient.
   */
  virtual void reserve_nodes (const unsigned int nn) = 0; 
  
  /**
   * Returns the number of elements in the mesh.
   */
  virtual unsigned int n_elem () const = 0; 

  /**
   * Returns a number greater than or equal to the maximum element id in the
   * mesh.
   */
  virtual unsigned int max_elem_id () const = 0;

  /**
   * Reserves space for a known number of elements.
   * Note that this method may or may not do anything, depending
   * on the actual \p Mesh implementation.  If you know the number
   * of elements you will add and call this method before repeatedly
   * calling \p add_point() the implementation will be more efficient.
   */
  virtual void reserve_elem (const unsigned int ne) = 0; 

  /**
   * Updates parallel caches so that methods like n_elem() 
   * accurately reflect changes on other processors
   */
  virtual void update_parallel_id_counts () = 0;

  /**
   * Returns the number of active elements in the mesh.  Implemented
   * in terms of active_element_iterators.
   */
  virtual unsigned int n_active_elem () const = 0;

  /**
   * Returns the number of elements on processor \p proc.
   */
  unsigned int n_elem_on_proc (const unsigned int proc) const;

  /**
   * Returns the number of elements on the local processor.
   */
  unsigned int n_local_elem () const
  { return this->n_elem_on_proc (libMesh::processor_id()); }

  /**
   * Returns the number of elements owned by no processor.
   */
  unsigned int n_unpartitioned_elem () const
  { return this->n_elem_on_proc (DofObject::invalid_processor_id); }

  /**
   * Returns the number of active elements on processor \p proc.
   */
  unsigned int n_active_elem_on_proc (const unsigned int proc) const;

  /**
   * Returns the number of active elements on the local processor.
   */
  unsigned int n_active_local_elem () const
  { return this->n_active_elem_on_proc (libMesh::processor_id()); }
  
  /**
   * This function returns the number of elements that will be written
   * out in the Tecplot format.  For example, a 9-noded quadrilateral will
   * be broken into 4 linear sub-elements for plotting purposes.  Thus, for
   * a mesh of 2 \p QUAD9 elements  \p n_tecplot_elem() will return 8.
   * Implemented in terms of element_iterators.
   */
  unsigned int n_sub_elem () const;

  /**
   * Same, but only counts active elements.
   */
  unsigned int n_active_sub_elem () const;
  
  /**
   * Return a constant reference (for reading only) to the
   * \f$ i^{th} \f$ point.
   */  
  virtual const Point& point (const unsigned int i) const = 0;

  /**
   * Return a constant reference (for reading only) to the
   * \f$ i^{th} \f$ node.
   */  
  virtual const Node& node (const unsigned int i) const = 0;
  
  /**
   * Return a reference to the \f$ i^{th} \f$ node.
   */  
  virtual Node& node (const unsigned int i) = 0;
  
  /**
   * Return a pointer to the \f$ i^{th} \f$ node.
   */  
  virtual const Node* node_ptr (const unsigned int i) const = 0;

  /**
   * Return a pointer to the \f$ i^{th} \f$ node.
   */  
  virtual Node* & node_ptr (const unsigned int i) = 0;

  /**
   * Return a pointer to the \f$ i^{th} \f$ element.
   */
  virtual Elem* elem (const unsigned int i) const = 0;

  /**
   * Add a new \p Node at \p Point \p p to the end of the vertex array,
   * with processor_id \p procid.
   * Use DofObject::invalid_processor_id (default) to add a node to all
   * processors, or libMesh::processor_id() to add a node to the local
   * processor only.
   * If adding a node locally, passing an \p id other than
   * DofObject::invalid_id will set that specific node id.  Only
   * do this in parallel if you are manually keeping ids consistent.
   */
  virtual Node* add_point (const Point& p,
			   const unsigned int id = DofObject::invalid_id,
			   const unsigned int proc_id =
			     DofObject::invalid_processor_id) = 0;

  /**
   * Add \p Node \p n to the end of the vertex array.
   */
  virtual Node* add_node (Node* n) = 0;

  /**
   * Removes the Node n from the mesh.
   */
  virtual void delete_node (Node* n) = 0;
  
  /**
   * Changes the id of node \p old_id, both by changing node(old_id)->id() and
   * by moving node(old_id) in the mesh's internal container.  No element with
   * the id \p new_id should already exist.
   */
  virtual void renumber_node (unsigned int old_id, unsigned int new_id) = 0;
		      
  /**
   * Add elem \p e to the end of the element array.
   * To add an element locally, set e->processor_id() before adding it.
   * To ensure a specific element id, call e->set_id() before adding it;
   * only do this in parallel if you are manually keeping ids consistent.
   */
  virtual Elem* add_elem (Elem* e) = 0;

  /**
   * Insert elem \p e to the element array, preserving its id
   * and replacing/deleting any existing element with the same id.
   */
  virtual Elem* insert_elem (Elem* e) = 0;

  /**
   * Removes element \p e from the mesh. Note that calling this
   * method may produce isolated nodes, i.e. nodes not connected
   * to any element.  This method must be implemented in derived classes
   * in such a way that it does not invalidate element iterators.
   */
  virtual void delete_elem (Elem* e) = 0;

  /**
   * Changes the id of element \p old_id, both by changing elem(old_id)->id()
   * and by moving elem(old_id) in the mesh's internal container.  No element
   * with the id \p new_id should already exist.
   */
  virtual void renumber_elem (unsigned int old_id, unsigned int new_id) = 0;

  /**
   * Locate element face (edge in 2D) neighbors.  This is done with the help
   * of a \p std::map that functions like a hash table.  
   * After this routine is called all the elements with a \p NULL neighbor
   * pointer are guaranteed to be on the boundary.  Thus this routine is
   * useful for automatically determining the boundaries of the domain.
   * If reset_remote_elements is left to false, remote neighbor links are not
   * reset and searched for in the local mesh.  If reset_current_list is
   * left as true, then any existing links will be reset before initiating
   * the algorithm, while honoring the value of the reset_remote_elements
   * flag.
   */
  virtual void find_neighbors (const bool reset_remote_elements = false,
			       const bool reset_current_list    = true) = 0;
  
  /**
   * After partitoning a mesh it is useful to renumber the nodes and elements
   * so that they lie in contiguous blocks on the processors.  This method
   * does just that.
   */
  virtual void renumber_nodes_and_elements () = 0;    

    /**
     * There is no reason for a user to ever call this function.
     *
     * This function restores a previously broken element/node numbering such that
     * \p mesh.node(n)->id() == n. 
     */
  virtual void fix_broken_node_and_element_numbering () = 0;
  

#ifdef LIBMESH_ENABLE_AMR
  /**
   * Delete subactive (i.e. children of coarsened) elements.
   * This removes all elements descended from currently active
   * elements in the mesh.
   */
  virtual bool contract () = 0;
#endif

  /**
   * Prepare a newly created (or read) mesh for use.
   * This involves 3 steps:
   *  1.) call \p find_neighbors()
   *  2.) call \p partition()
   *  3.) call \p renumber_nodes_and_elements() 
   *
   * The read_xda_file boolean flag is true when prepare_for_use
   * is called from Mesh::read after reading an xda file.  It prevents
   * the renumbering of nodes and elements.  In general, leave this at
   * the default value of false.
   *
   * skip_renumber is currently set to TRUE to work around an I/O bug
   */
  void prepare_for_use (const bool skip_renumber_nodes_and_elements=true);
  
  /**
   * Call the default partitioner (currently \p metis_partition()).
   */
  virtual void partition (const unsigned int n_parts=libMesh::n_processors());

  /**
   * If true is passed in then this mesh will no longer be (re)partitioned.
   * It would probably be a bad idea to call this on a Serial Mesh _before_
   * the first partitioning has happened... because no elements would get assigned
   * to your processor pool.
   *
   * Note that turning on skip_partitioning() can have adverse effects on your
   * performance when using AMR... ie you could get large load imbalances.
   *
   * However you might still want to use this if the communication and computation
   * of the rebalance and repartition is too high for your application.
   */
  void skip_partitioning(bool skip) { _skip_partitioning = skip; }
  bool skip_partitioning() { return _skip_partitioning; }
  
  /**
   * Returns the number of subdomains in the global mesh. Subdomains correspond
   * to separate subsets of the mesh which could correspond e.g. to different 
   * materials in a solid mechanics application, or regions where different
   * physical processes are important.  The subdomain mapping is independent
   * from the parallel decomposition.
   */
  unsigned int n_subdomains () const;

  /**
   * Returns the number of partitions which have been defined via
   * a call to either mesh.partition() or by building a Partitioner
   * object and calling partition.  Note that the partitioner objects
   * are responsible for setting this value.
   */
  unsigned int n_partitions () const
  { return _n_parts; }
  
  /**
   * @returns the number of processors used in the
   * current simulation.
   */
  unsigned int n_processors () const
  { return libMesh::n_processors(); }

  /**
   * @returns the subdomain id for this processor.
   */
  unsigned int processor_id () const
  { return libMesh::processor_id(); }

  /**
   * @returns a string containing relevant information
   * about the mesh.
   */
  std::string get_info () const;

  /**
   * Prints relevant information about the mesh.
   */
  void print_info (std::ostream& os=libMesh::out) const;

  /**
   * Equivalent to calling print_info() above, but now you can write:
   * Mesh mesh;
   * libMesh::out << mesh << std::endl;
   */
  friend std::ostream& operator << (std::ostream& os, const MeshBase& m);

  /**
   * Interfaces for reading/writing a mesh to/from a file.  Must be
   * implemented in derived classes.
   */
  virtual void read  (const std::string& name, MeshData* mesh_data=NULL,
		      bool skip_renumber_nodes_and_elements=false) = 0;
  virtual void write (const std::string& name, MeshData* mesh_data=NULL) = 0;

  /**
   * Converts a mesh with higher-order
   * elements into a mesh with linear elements.  For 
   * example, a mesh consisting of \p Tet10 will be converted
   * to a mesh with \p Tet4 etc.
   */
  virtual void all_first_order () = 0;

  /**
   * Converts a (conforming, non-refined) mesh with linear 
   * elements into a mesh with second-order elements.  For 
   * example, a mesh consisting of \p Tet4 will be converted
   * to a mesh with \p Tet10 etc.  Note that for some elements
   * like \p Hex8 there exist @e two higher order equivalents,
   * \p Hex20 and \p Hex27.  When \p full_ordered is \p true
   * (default), then \p Hex27 is built.  Otherwise, \p Hex20
   * is built.  The same holds obviously for \p Quad4, \p Prism6
   * ...
   */
  virtual void all_second_order (const bool full_ordered=true) = 0;

  /**
   * We need an empty, generic class to act as a predicate for this
   * and derived mesh classes.
   */
  typedef Predicates::multi_predicate Predicate;

  /**
   * structs for the element_iterator's.
   * Note that these iterators were designed so that derived mesh classes could use the
   * _same_ base class iterators interchangeably.  Their definition comes later in the
   * header file.
   */
  struct element_iterator;
  struct const_element_iterator;

  /**
   * structs for the node_iterator's.
   * Note that these iterators were designed so that derived mesh classes could use the
   * _same_ base class iterators interchangeably.  Their definition comes later in the
   * header file.
   */
  struct node_iterator;
  struct const_node_iterator;

  /**
   * In a few (very rare) cases, the user may have manually tagged the
   * elements with specific processor IDs by hand, without using a
   * partitioner.  In this case, the Mesh will not know that the total
   * number of partitions, _n_parts, has changed, unless you call this
   * function.  This is an O(N active elements) calculation.  The return
   * value is the number of partitions, and _n_parts is also set by
   * this function.  
   */
  unsigned int recalculate_n_partitions();

  /**
   * \p returns a pointer to a \p PointLocatorBase object for this
   * mesh, constructing a master PointLocator first if necessary.
   * This should never be used in threaded or non-parallel_only code,
   * and so is deprecated.
   */
  const PointLocatorBase& point_locator () const;

  /**
   * \p returns a pointer to a subordinate \p PointLocatorBase object
   * for this mesh, constructing a master PointLocator first if
   * necessary.  This should not be used in threaded or
   * non-parallel_only code unless the master has already been
   * constructed.
   */
  AutoPtr<PointLocatorBase> sub_point_locator () const;

  /**
   * Releases the current \p PointLocator object.
   */
  void clear_point_locator ();

  /**
   * Verify id and processor_id consistency of our elements and
   * nodes containers.
   * Calls libmesh_assert() on each possible failure.
   * Currently only implemented on ParallelMesh; a serial data
   * structure is much harder to get out of sync.
   */
  virtual void libmesh_assert_valid_parallel_ids() const {}

public:


  
  /**
   * Elem iterator accessor functions.  These must be defined in
   * Concrete base classes.
   */
  virtual element_iterator elements_begin                   () = 0;
  virtual element_iterator elements_end                     () = 0;
  virtual element_iterator active_elements_begin            () = 0;
  virtual element_iterator active_elements_end              () = 0;
  virtual element_iterator ancestor_elements_begin          () = 0;
  virtual element_iterator ancestor_elements_end            () = 0;
  virtual element_iterator subactive_elements_begin         () = 0;
  virtual element_iterator subactive_elements_end           () = 0;
  virtual element_iterator not_active_elements_begin        () = 0;
  virtual element_iterator not_active_elements_end          () = 0;
  virtual element_iterator not_ancestor_elements_begin      () = 0;
  virtual element_iterator not_ancestor_elements_end        () = 0;
  virtual element_iterator not_subactive_elements_begin     () = 0;
  virtual element_iterator not_subactive_elements_end       () = 0;
  virtual element_iterator local_elements_begin             () = 0;
  virtual element_iterator local_elements_end               () = 0;
  virtual element_iterator not_local_elements_begin         () = 0;
  virtual element_iterator not_local_elements_end           () = 0;
  virtual element_iterator active_local_elements_begin      () = 0;
  virtual element_iterator active_local_elements_end        () = 0;
  virtual element_iterator active_not_local_elements_begin  () = 0;
  virtual element_iterator active_not_local_elements_end    () = 0;
  virtual element_iterator level_elements_begin             (const unsigned int level  ) = 0;
  virtual element_iterator level_elements_end               (const unsigned int level  ) = 0;
  virtual element_iterator not_level_elements_begin         (const unsigned int level  ) = 0;
  virtual element_iterator not_level_elements_end           (const unsigned int level  ) = 0;
  virtual element_iterator local_level_elements_begin       (const unsigned int level  ) = 0;
  virtual element_iterator local_level_elements_end         (const unsigned int level  ) = 0;
  virtual element_iterator local_not_level_elements_begin   (const unsigned int level  ) = 0;
  virtual element_iterator local_not_level_elements_end     (const unsigned int level  ) = 0;
  virtual element_iterator pid_elements_begin               (const unsigned int proc_id) = 0;
  virtual element_iterator pid_elements_end                 (const unsigned int proc_id) = 0;
  virtual element_iterator type_elements_begin              (const ElemType type       ) = 0;
  virtual element_iterator type_elements_end                (const ElemType type       ) = 0;
  virtual element_iterator active_type_elements_begin       (const ElemType type       ) = 0;
  virtual element_iterator active_type_elements_end         (const ElemType type       ) = 0;
  virtual element_iterator active_pid_elements_begin        (const unsigned int proc_id) = 0;
  virtual element_iterator active_pid_elements_end          (const unsigned int proc_id) = 0;
  virtual element_iterator unpartitioned_elements_begin     () = 0;
  virtual element_iterator unpartitioned_elements_end       () = 0;
  virtual element_iterator active_local_subdomain_elements_begin         (const unsigned int subdomain_id) = 0;
  virtual element_iterator active_local_subdomain_elements_end           (const unsigned int subdomain_id) = 0;
  

  
  
  /**
   * const Elem iterator accessor functions.
   */
  virtual const_element_iterator elements_begin                   () const = 0;
  virtual const_element_iterator elements_end                     () const = 0;
  virtual const_element_iterator active_elements_begin            () const = 0;
  virtual const_element_iterator active_elements_end              () const = 0;
  virtual const_element_iterator ancestor_elements_begin          () const = 0;
  virtual const_element_iterator ancestor_elements_end            () const = 0;
  virtual const_element_iterator subactive_elements_begin         () const = 0;
  virtual const_element_iterator subactive_elements_end           () const = 0;
  virtual const_element_iterator not_active_elements_begin        () const = 0;
  virtual const_element_iterator not_active_elements_end          () const = 0;
  virtual const_element_iterator not_ancestor_elements_begin      () const = 0;
  virtual const_element_iterator not_ancestor_elements_end        () const = 0;
  virtual const_element_iterator not_subactive_elements_begin     () const = 0;
  virtual const_element_iterator not_subactive_elements_end       () const = 0;
  virtual const_element_iterator local_elements_begin             () const = 0;
  virtual const_element_iterator local_elements_end               () const = 0;
  virtual const_element_iterator not_local_elements_begin         () const = 0;
  virtual const_element_iterator not_local_elements_end           () const = 0;
  virtual const_element_iterator active_local_elements_begin      () const = 0;
  virtual const_element_iterator active_local_elements_end        () const = 0;
  virtual const_element_iterator active_not_local_elements_begin  () const = 0;
  virtual const_element_iterator active_not_local_elements_end    () const = 0;
  virtual const_element_iterator level_elements_begin             (const unsigned int level)   const = 0;
  virtual const_element_iterator level_elements_end               (const unsigned int level)   const = 0;
  virtual const_element_iterator not_level_elements_begin         (const unsigned int level)   const = 0;
  virtual const_element_iterator not_level_elements_end           (const unsigned int level)   const = 0;
  virtual const_element_iterator local_level_elements_begin       (const unsigned int level)   const = 0;
  virtual const_element_iterator local_level_elements_end         (const unsigned int level)   const = 0;
  virtual const_element_iterator local_not_level_elements_begin   (const unsigned int level)   const = 0;
  virtual const_element_iterator local_not_level_elements_end     (const unsigned int level)   const = 0;
  virtual const_element_iterator pid_elements_begin               (const unsigned int proc_id) const = 0;
  virtual const_element_iterator pid_elements_end                 (const unsigned int proc_id) const = 0;
  virtual const_element_iterator type_elements_begin              (const ElemType type)        const = 0;
  virtual const_element_iterator type_elements_end                (const ElemType type)        const = 0;
  virtual const_element_iterator active_type_elements_begin       (const ElemType type)        const = 0;
  virtual const_element_iterator active_type_elements_end         (const ElemType type)        const = 0;
  virtual const_element_iterator active_pid_elements_begin        (const unsigned int proc_id) const = 0;
  virtual const_element_iterator active_pid_elements_end          (const unsigned int proc_id) const = 0;
  virtual const_element_iterator unpartitioned_elements_begin     () const = 0;
  virtual const_element_iterator unpartitioned_elements_end       () const = 0;
  virtual const_element_iterator active_local_subdomain_elements_begin (const unsigned int subdomain_id) const = 0;
  virtual const_element_iterator active_local_subdomain_elements_end   (const unsigned int subdomain_id) const = 0;

  
  /**
   * non-const Node iterator accessor functions.
   */
  virtual node_iterator nodes_begin        () = 0;
  virtual node_iterator nodes_end          () = 0;
  virtual node_iterator active_nodes_begin () = 0;
  virtual node_iterator active_nodes_end   () = 0;
  virtual node_iterator local_nodes_begin  () = 0;
  virtual node_iterator local_nodes_end    () = 0;
  virtual node_iterator pid_nodes_begin    (const unsigned int proc_id) = 0;
  virtual node_iterator pid_nodes_end      (const unsigned int proc_id) = 0;


  /**
   * const Node iterator accessor functions.
   */
  virtual const_node_iterator nodes_begin        () const = 0;
  virtual const_node_iterator nodes_end          () const = 0;
  virtual const_node_iterator active_nodes_begin () const = 0;
  virtual const_node_iterator active_nodes_end   () const = 0;
  virtual const_node_iterator local_nodes_begin  () const = 0;
  virtual const_node_iterator local_nodes_end    () const = 0;
  virtual const_node_iterator pid_nodes_begin    (const unsigned int proc_id) const = 0;
  virtual const_node_iterator pid_nodes_end      (const unsigned int proc_id) const = 0;


  
protected:



  
  

  /**
   * Returns a writeable reference to the number of partitions.
   */
  unsigned int& set_n_partitions ()
  { return _n_parts; }
  
  /**
   * The number of partitions the mesh has.  This is set by
   * the partitioners, and may not be changed directly by
   * the user.
   * **NOTE** The number of partitions *need not* equal
   * libMesh::n_processors(), consider for example the case
   * where you simply want to partition a mesh on one
   * processor and view the result in GMV.
   */
  unsigned int _n_parts;
  
  /**
   * The logical dimension of the mesh.
   */     
  unsigned int _dim;

  /**
   * Flag indicating if the mesh has been prepared for use.
   */
  bool _is_prepared;
  
  /**
   * A \p PointLocator class for this mesh. 
   * This will not actually be built unless needed. Further, since we want 
   * our \p point_locator() method to be \p const (yet do the dynamic allocating)
   * this needs to be mutable.  Since the PointLocatorBase::build() member is used, 
   * and it operates on a constant reference to the mesh, this is OK.
   */
  mutable AutoPtr<PointLocatorBase> _point_locator;

  /**
   * A partitioner to use at each prepare_for_use().
   *
   * This will be built in the constructor of each derived class, but
   * can be replaced by the user through the partitioner() accessor.
   */
  AutoPtr<Partitioner> _partitioner;

  /**
   * If this is true then no partitioning should be done.
   */
  bool _skip_partitioning;
  
  /**
   * The partitioner class is a friend so that it can set
   * the number of partitions.
   */
  friend class Partitioner;

  /**
   * Make the \p BoundaryInfo class a friend so that
   * it can create and interact with \p BoundaryMesh.
   */
  friend class BoundaryInfo;

};











/**
 * The definition of the element_iterator struct.
 */
struct
MeshBase::element_iterator :
variant_filter_iterator<MeshBase::Predicate,
			Elem*>
{
  // Templated forwarding ctor -- forwards to appropriate variant_filter_iterator ctor
  template <typename PredType, typename IterType>
  element_iterator (const IterType& d,
		    const IterType& e,
		    const PredType& p ) :
    variant_filter_iterator<MeshBase::Predicate,
			    Elem*>(d,e,p) {}
};




/**
 * The definition of the const_element_iterator struct.  It is similar to the regular
 * iterator above, but also provides an additional conversion-to-const ctor.
 */
struct
MeshBase::const_element_iterator :
variant_filter_iterator<MeshBase::Predicate,
			Elem* const,
			Elem* const&,
			Elem* const*>
{
  // Templated forwarding ctor -- forwards to appropriate variant_filter_iterator ctor
  template <typename PredType, typename IterType>
  const_element_iterator (const IterType& d,
			  const IterType& e,
			  const PredType& p ) :
    variant_filter_iterator<MeshBase::Predicate,
			    Elem* const,
			    Elem* const&,
			    Elem* const*>(d,e,p)  {}


  // The conversion-to-const ctor.  Takes a regular iterator and calls the appropriate
  // variant_filter_iterator copy constructor.  Note that this one is *not* templated!
  const_element_iterator (const MeshBase::element_iterator& rhs) :
    variant_filter_iterator<Predicate,
			    Elem* const,
			    Elem* const&,
			    Elem* const*>(rhs)
  {
    // libMesh::out << "Called element_iterator conversion-to-const ctor." << std::endl;
  }
};







/**
 * The definition of the node_iterator struct.
 */
struct
MeshBase::node_iterator :
variant_filter_iterator<MeshBase::Predicate,
			Node*>
{
  // Templated forwarding ctor -- forwards to appropriate variant_filter_iterator ctor
  template <typename PredType, typename IterType>
  node_iterator (const IterType& d,
		 const IterType& e,
		 const PredType& p ) :
    variant_filter_iterator<MeshBase::Predicate,
			    Node*>(d,e,p) {}
};




/**
 * The definition of the const_node_iterator struct.  It is similar to the regular
 * iterator above, but also provides an additional conversion-to-const ctor.
 */
struct
MeshBase::const_node_iterator :
variant_filter_iterator<MeshBase::Predicate,
			Node* const,
			Node* const &,
			Node* const *>
{
  // Templated forwarding ctor -- forwards to appropriate variant_filter_iterator ctor
  template <typename PredType, typename IterType>
  const_node_iterator (const IterType& d,
		       const IterType& e,
		       const PredType& p ) :
    variant_filter_iterator<MeshBase::Predicate,
			    Node* const,
			    Node* const &,
			    Node* const *>(d,e,p)  {}


  // The conversion-to-const ctor.  Takes a regular iterator and calls the appropriate
  // variant_filter_iterator copy constructor.  Note that this one is *not* templated!
  const_node_iterator (const MeshBase::node_iterator& rhs) :
    variant_filter_iterator<Predicate,
			    Node* const,
			    Node* const &,
			    Node* const *>(rhs)
  {
    // libMesh::out << "Called node_iterator conversion-to-const ctor." << std::endl;
  }
};


} // namespace libMesh

#endif