Ifpack_Partitioner: A class to decompose local Ifpack_Graph's. More...

#include <Ifpack_Partitioner.h>

Inheritance diagram for Ifpack_Partitioner:

Public Member Functions
virtual	~Ifpack_Partitioner ()
	Destructor. More...

virtual int	NumLocalParts () const =0
	Returns the number of computed local partitions. More...

virtual int	OverlappingLevel () const =0
	Returns the overlapping level. More...

virtual int	operator() (int MyRow) const =0
	Returns the local non-overlapping partition ID of the specified row. More...

virtual int	operator() (int i, int j) const =0
	Returns the local overlapping partition ID of the j-th node in partition i. More...

virtual int	NumRowsInPart (const int Part) const =0
	Returns the number of rows contained in specified partition. More...

virtual int	RowsInPart (const int Part, int *List) const =0
	Copies into List the rows in the (overlapping) partition Part. More...

virtual const int *	NonOverlappingPartition () const =0
	Returns a pointer to the integer vector containing the non-overlapping partition ID of each local row. More...

virtual int	SetParameters (Teuchos::ParameterList &List)=0
	Sets all the parameters for the partitioner. More...

virtual int	Compute ()=0
	Computes the partitions. Returns 0 if successful. More...

virtual bool	IsComputed ()=0
	Returns true if partitions have been computed successfully. More...

virtual std::ostream &	Print (std::ostream &os) const =0
	Prints basic information about the partitioning object. More...

Detailed Description

Ifpack_Partitioner: A class to decompose local Ifpack_Graph's.

Class Ifpack_Partitioner enables the decomposition of a local Ifpack_Graph's. It is supposed that the graph refers to a localized matrix (that is, a matrix that has been filtered through Ifpack_LocalFilter).

The overloaded operator (int i) can be used to extract the local partition ID of local row i.

The partitions created by Ifpack_Partitioner derived clased are non-overlapping in graph sense. This means that each row (or, more approriately, vertex) of G is assigned to exactly one partition.

Partitioner can be extended using the functionalities of class Ifpack_OverlappingPartitioner (itself derived from Ifpack_Partitioner. This class extends the non-overlapping partitions by the required amount of overlap, considering local nodes only (that is, this overlap do not modify the overlap among the processes).

Ifpack_Partitioner is a pure virtual class. Concrete implementations are:

Ifpack_LinearPartitioner, which allows the decomposition of the rows of the graph in simple consecutive chunks;
Ifpack_METISPartitioner, which calls METIS to decompose the graph (this requires the configuration option –enable-ifpack-metis);
Ifpack_GreedyPartitioner, a simple greedy algorith;
Ifpack_EquationPartitioner, which creates NumPDEEqns parts (where NumPDEEqns is the number of equations in the linear system). It is supposed that all the equations referring to the same grid node are ordered consecutively. Besides, the number of equations per node must be constant in the domain.

Generically, a constructor requires an Ifpack_Graph object. Ifpack_Graph is a pure virtual class. Concrete implentations are:

Ifpack_Graph_Epetra_CrsGraph, a light-weight class to wrap Epetra_CrsGraph objects as Ifpack_Graph objects;
Ifpack_Graph_Epetra_RowMatrix, a light-weight class to wrap Epetra_RowMatrix objects as Ifpack_Graph objects.

An example of use is an Ifpack_Partitioner derived class is as follows:

#include "Ifpack_Partitioner.h"
#include "Ifpack_LinearPartitioner.h"
#include "Ifpack_Graph.h"
#include "Ifpack_Graph_Epetra_CrsGraph.h"
...
Epetra_CrsMatrix* A;         // A is filled
// create the wrapper from Epetra_CrsGraph
Ifpack_Graph* Graph = new Ifpack_Graph_Epetra_CrsGraph(A);
// we aim to create non-overlapping partitions only
Ifpack_Partitioner Partitioner(Graph);
Ifpack_Partitioner* Partitioner;
Partitioner = new Ifpack_Graph_Epetra_CrsGraph(&A);
// we want 16 local parts
List.set("partitioner: local parts", 16);
// and an overlap of 0 among the local parts (default option)
List.set("partitioner: overlap", 0);
// decompose the graph
Partitioner.Create(List);
// now Graph can be deleted, as Partitioner contains all the
// necessary information to use the partitions
delete Graph;
// we can get the number of parts actually created...
int NumParts = Partitioner.NumParts();
// ... and the number of rows in each of them
for (int i = 0 ; i < NumParts ; ++i) {
  cout << "rows in " << i << "=" << Partitioner.RowsInPart(i);
}
// .. and, for non-overlapping partitions only, the partition ID
// for each local row simply using:
for (int i = 0 ; i < A->NumMyRows() ; ++i)
  cout << "Partition[" << i <<"] = " << Partitioner(i) << endl;

When overlapping partitiones are created, the user can get the row ID contained in each partition as follows:

for (int i = 0 ; i < NumParts ; ++i) {
  for (int j = 0 ; j < Partitioner.RowsInPart(i) ; ++j) {
    cout << "Partition " << i << ", contains local row "
         << Partitioner(i,j) << endl;
  }
}