Epetra_BlockMap Class Reference

Epetra_BlockMap: A class for partitioning block element vectors and matrices. More...

#include <Epetra_BlockMap.h>

Inheritance diagram for Epetra_BlockMap:

Collaboration diagram for Epetra_BlockMap:

Public Member Functions
template<>
bool	GlobalIndicesIsType () const
template<>
bool	GlobalIndicesIsType () const
Constructors/destructors
	Epetra_BlockMap (int NumGlobalElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap constructor for a Epetra-defined uniform linear distribution of constant size elements. More...
	Epetra_BlockMap (long long NumGlobalElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (long long NumGlobalElements, int ElementSize, long long IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (int NumGlobalElements, int NumMyElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap constructor for a user-defined linear distribution of constant size elements. More...
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, int ElementSize, long long IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (int NumGlobalElements, int NumMyElements, const int *MyGlobalElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap constructor for a user-defined arbitrary distribution of constant size elements. More...
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, const long long *MyGlobalElements, int ElementSize, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, const long long *MyGlobalElements, int ElementSize, long long IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (int NumGlobalElements, int NumMyElements, const int *MyGlobalElements, const int *ElementSizeList, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap constructor for a user-defined arbitrary distribution of variable size elements. More...
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, const long long *MyGlobalElements, const int *ElementSizeList, int IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (long long NumGlobalElements, int NumMyElements, const long long *MyGlobalElements, const int *ElementSizeList, long long IndexBase, const Epetra_Comm &Comm)
	Epetra_BlockMap (long long NumGlobal_Elements, int NumMy_Elements, const long long *myGlobalElements, int ElementSize, int indexBase, const Epetra_Comm &comm, bool UserIsDistributedGlobal, long long UserMinAllGID, long long UserMaxAllGID)
	Epetra_BlockMap constructor for a user-defined arbitrary distribution of constant size elements, where the user provides all the globals. More...
	Epetra_BlockMap (long long NumGlobal_Elements, int NumMy_Elements, const long long *myGlobalElements, int ElementSize, long long indexBase, const Epetra_Comm &comm, bool UserIsDistributedGlobal, long long UserMinAllGID, long long UserMaxAllGID)
	Epetra_BlockMap (int NumGlobal_Elements, int NumMy_Elements, const int *myGlobalElements, int ElementSize, int indexBase, const Epetra_Comm &comm, bool UserIsDistributedGlobal, int UserMinAllGID, int UserMaxAllGID)
	Epetra_BlockMap (const Epetra_BlockMap &map)
	Epetra_BlockMap copy constructor.
virtual	~Epetra_BlockMap (void)
	Epetra_BlockMap destructor.
Local/Global ID accessor methods
int	RemoteIDList (int NumIDs, const int *GIDList, int *PIDList, int *LIDList) const
	Returns the processor IDs and corresponding local index value for a given list of global indices. More...
int	RemoteIDList (int NumIDs, const long long *GIDList, int *PIDList, int *LIDList) const
int	RemoteIDList (int NumIDs, const int *GIDList, int *PIDList, int *LIDList, int *SizeList) const
	Returns the processor IDs, corresponding local index value, and element size for a given list of global indices. More...
int	RemoteIDList (int NumIDs, const long long *GIDList, int *PIDList, int *LIDList, int *SizeList) const
int	LID (int GID) const
	Returns local ID of global ID, return -1 if not found on this processor.
int	LID (long long GID) const
int	GID (int LID) const
	Returns global ID of local ID, return IndexBase-1 if not found on this processor.
long long	GID64 (int LID) const
int	FindLocalElementID (int PointID, int &ElementID, int &ElementOffset) const
	Returns the LID of the element that contains the given local PointID, and the Offset of the point in that element.
bool	MyGID (int GID_in) const
	Returns true if the GID passed in belongs to the calling processor in this map, otherwise returns false.
bool	MyGID (long long GID_in) const
bool	MyLID (int lid) const
	Returns true if the LID passed in belongs to the calling processor in this map, otherwise returns false.
int	MinAllGID () const
	Returns the minimum global ID across the entire map.
long long	MinAllGID64 () const
int	MaxAllGID () const
	Returns the maximum global ID across the entire map.
long long	MaxAllGID64 () const
int	MinMyGID () const
	Returns the minimum global ID owned by this processor.
long long	MinMyGID64 () const
int	MaxMyGID () const
	Returns the maximum global ID owned by this processor.
long long	MaxMyGID64 () const
int	MinLID () const
	The minimum local index value on the calling processor.
int	MaxLID () const
	The maximum local index value on the calling processor.
Size and dimension accessor functions
int	NumGlobalElements () const
	Number of elements across all processors.
long long	NumGlobalElements64 () const
int	NumMyElements () const
	Number of elements on the calling processor.
int	MyGlobalElements (int *MyGlobalElementList) const
	Puts list of global elements on this processor into the user-provided array.
int	MyGlobalElements (long long *MyGlobalElementList) const
int	MyGlobalElementsPtr (int *&MyGlobalElementList) const
int	MyGlobalElementsPtr (long long *&MyGlobalElementList) const
int	ElementSize () const
	Returns the size of elements in the map; only valid if map has constant element size.
int	ElementSize (int LID) const
	Size of element for specified LID.
int	FirstPointInElement (int LID) const
	Returns the requested entry in the FirstPointInElementList; see FirstPointInElementList() for details. More...
int	IndexBase () const
	Index base for this map.
long long	IndexBase64 () const
int	NumGlobalPoints () const
	Number of global points for this map; equals the sum of all element sizes across all processors.
long long	NumGlobalPoints64 () const
int	NumMyPoints () const
	Number of local points for this map; equals the sum of all element sizes on the calling processor.
int	MinMyElementSize () const
	Minimum element size on the calling processor.
int	MaxMyElementSize () const
	Maximum element size on the calling processor.
int	MinElementSize () const
	Minimum element size across all processors.
int	MaxElementSize () const
	Maximum element size across all processors.
Miscellaneous boolean tests
bool	UniqueGIDs () const
	Returns true if map GIDs are 1-to-1. More...
bool	GlobalIndicesInt () const
	Returns true if map create with int NumGlobalElements.
bool	GlobalIndicesLongLong () const
	Returns true if map create with long long NumGlobalElements.
template<typename int_type >
bool	GlobalIndicesIsType () const
bool	GlobalIndicesTypeValid () const
bool	GlobalIndicesTypeMatch (const Epetra_BlockMap &other) const
bool	ConstantElementSize () const
	Returns true if map has constant element size.
bool	SameBlockMapDataAs (const Epetra_BlockMap &Map) const
bool	SameAs (const Epetra_BlockMap &Map) const
	Returns true if this and Map are identical maps.
bool	PointSameAs (const Epetra_BlockMap &Map) const
	Returns true if this and Map have identical point-wise structure. More...
bool	LinearMap () const
	Returns true if the global ID space is contiguously divided (but not necessarily uniformly) across all processors.
bool	DistributedGlobal () const
	Returns true if map is defined across more than one processor.
Array accessor functions
int *	MyGlobalElements () const
	Pointer to internal array containing list of global IDs assigned to the calling processor.
long long *	MyGlobalElements64 () const
void	MyGlobalElements (const int *&IntGIDs, const long long *&LLGIDs) const
void	MyGlobalElements (int *&IntGIDs, long long *&LLGIDs)
int *	FirstPointInElementList () const
	Pointer to internal array containing a mapping between the local elements and the first local point number in each element. More...
int *	ElementSizeList () const
	List of the element sizes corresponding to the array MyGlobalElements().
int *	PointToElementList () const
	For each local point, indicates the local element ID that the point belongs to.
int	ElementSizeList (int *ElementSizeList) const
	Same as ElementSizeList() except it fills the user array that is passed in.
int	FirstPointInElementList (int *FirstPointInElementList) const
	Same as FirstPointInElementList() except it fills the user array that is passed in.
int	PointToElementList (int *PointToElementList) const
	Same as PointToElementList() except it fills the user array that is passed in.
Miscellaneous
virtual void	Print (std::ostream &os) const
	Print object to an output stream.
const Epetra_Comm &	Comm () const
	Access function for Epetra_Comm communicator.
bool	IsOneToOne () const
Epetra_BlockMap &	operator= (const Epetra_BlockMap &map)
	Assignment Operator.
Expert Users and Developers Only
int	ReferenceCount () const
	Returns the reference count of BlockMapData. More...
const Epetra_BlockMapData *	DataPtr () const
	Returns a pointer to the BlockMapData instance this BlockMap uses. More...
Epetra_BlockMap *	RemoveEmptyProcesses () const
	Return a new BlockMap with processes with zero elements removed. More...
Epetra_BlockMap *	ReplaceCommWithSubset (const Epetra_Comm *Comm) const
	Replace this BlockMap's communicator with a subset communicator. More...
Public Member Functions inherited from Epetra_Object
	Epetra_Object (int TracebackModeIn=-1, bool set_label=true)
	Epetra_Object Constructor. More...
	Epetra_Object (const char *const Label, int TracebackModeIn=-1)
	Epetra_Object Constructor. More...
	Epetra_Object (const Epetra_Object &Object)
	Epetra_Object Copy Constructor. More...
virtual	~Epetra_Object ()
	Epetra_Object Destructor. More...
virtual int	ReportError (const std::string Message, int ErrorCode) const
	Error reporting method.
virtual void	SetLabel (const char *const Label)
	Epetra_Object Label definition using char *. More...
virtual const char *	Label () const
	Epetra_Object Label access funtion. More...

Protected Member Functions
void	CleanupData ()
Protected Member Functions inherited from Epetra_Object
std::string	toString (const int &x) const
std::string	toString (const long long &x) const
std::string	toString (const double &x) const

Protected Attributes
Epetra_BlockMapData *	BlockMapData_

Friends
class	Epetra_Directory
class	Epetra_LocalMap

Additional Inherited Members
Static Public Member Functions inherited from Epetra_Object
static void	SetTracebackMode (int TracebackModeValue)
	Set the value of the Epetra_Object error traceback report mode. More...
static int	GetTracebackMode ()
	Get the value of the Epetra_Object error report mode.
static std::ostream &	GetTracebackStream ()
	Get the output stream for error reporting.
Static Public Attributes inherited from Epetra_Object
static int	TracebackMode

Detailed Description

Epetra_BlockMap: A class for partitioning block element vectors and matrices.

It is often the case that multiple matrix and vector objects have an identical distribution

of elements on a parallel machine. The Epetra_BlockMap class keeps information that describes this distribution for matrices and vectors that have block elements. The definition of an element can vary depending on the situation. For vectors (and multi-vectors), an element is a span of one or more contiguous entries. For matrices, it is a span of one or more matrix rows. More generally, an element in the BlockMap class is an ordered list of points. (NOTE: Points do not have global ID's.) Two additional definitions useful in understanding the BlockMap class follow:

• BlockMap - A distributed ordered list of elements.
• First Point - First ordered point in an element

This class has a variety of constructors that can be separated into two categories:

1. Fixed element size constructors: All map elements have an identical size. This corresponds to a block partitioning of matrices and vectors where the element size is the same for all elements. A common example is multiple degrees of freedom per mesh node in finite element computations where the number of degrees of freedom is the same for all nodes.
2. Variable element size constructor: Map element sizes may vary and are individually defined via a list of element sizes. This is the most general case and corresponds to a variable block partitioning of the matrices and vectors. A common example is multiple degrees of freedom per mesh node in finite element computations where the number of degrees of freedom varies. This happens, for example, if regions have differing material types or there are chemical reactions in the simulation.

Epetra_BlockMap allows the storage and retrieval of the following information. Depending on the constructor that is used, some of the information is defined by the user and some is determined by the constructor. Once an Epetra_BlockMap is constructed any of the following can be obtained by calling a query function that has the same name as the attribute, e.g. to get the value of NumGlobalElements, you can call a function NumGlobalElements(). For attributes that are lists, the query functions return the list values in a user allocated array.

• NumGlobalElements - The total number of elements across all processors. If this parameter and NumMyElements are both passed in to the constructor, one of the three cases will apply:
  1. If NumGlobalElements = NumMyElements (and not equal to zero) the map is defined to be a local replicated map. In this case, objects constructed using this map will be identically replicated across all processors in the communicator.
  2. If NumGlobalElements = -1 and NumMyElements is passed in then NumGlobalElements will be computed as the sum of NumMyElements across all processors.
  3. If neither of the above is true, NumGlobalElements will be checked against the sum of NumMyElements across all processors. An error is issued if the comparison is not equal.
• NumMyElements - The number of elements owned by the calling processor.
• MyGlobalElements - A list of length NumMyElements that contains the global element IDs of the elements owned by the calling processor.
• ElementSize - The size of elements if the size of all elements is the same. This will be the case if the query function ConstantElementSize() returns true. Otherwise this value will be set to zero.
• ElementSizeList - A list of the element sizes for elements owned by the calling processor. This list is always accessible, even if the element sizes are all one or of constant value. However, in these cases, the ElementSizeList will not be generated unless a query for the list is called.
• IndexBase - The base integer value for indexed array references. Typically this is 0 for C/C++ and 1 for Fortran, but it can be set to any integer value.
• Comm - The Epetra_Comm communicator. This communicator can in turn be queried for processor rank and size information.

In addition to the information above that is passed in to or created by the Epetra_BlockMap constructor, the following attributes are computed and available via query to the user using the same scheme as above, e.g., use NumGlobalPoints() to get the value of NumGlobalPoints.

• NumGlobalPoints - The total number of points across all processors.
• NumMyPoints - The number of points on the calling processor.
• MinAllGID - The minimum global index value across all processors.
• MaxAllGID - The maximum global index value across all processors.
• MinMyGID - The minimum global index value on the calling processor.
• MaxMyGID - The maximum global index value on the calling processor.
• MinLID - The minimum local index value on the calling processor.
• MaxLID - The maximum local index value on the calling processor.
• MinElementSize - The minimum element size across all processors.
• MaxElementSize - The maximum element size across all processors.

The following functions allow boolean tests for certain properties.

• ConstantElementSize() - Returns true if the element size for this map is the same for all elements.
• LinearMap() - Returns true if the elements are distributed linear across processors, i.e., processor 0 gets the first n/p elements, processor 1 gets the next n/p elements, etc. where n is the number of elements and p is the number of processors.
• DistributedGlobal() - Returns true if the element space of the map spans more than one processor. This will be true in most cases, but will be false on in serial and for objects that are created via the derived Epetra_LocalMap class.

Warning

A Epetra_Comm object is required for all Epetra_BlockMap constructors.

error handling

Most methods in Epetra_BlockMap return an integer error code. If the error code is 0, then no error occurred. If > 0 then a warning error occurred. If < 0 then a fatal error occurred.

Epetra_BlockMap constructors will throw an exception of an error occurrs. These exceptions will alway be negative integer values as follows:

1. -1 NumGlobalElements < -1. Should be >= -1 (Should be >= 0 for first BlockMap constructor).
2. -2 NumMyElements < 0. Should be >= 0.
3. -3 ElementSize <= 0. Should be > 0.
4. -4 Invalid NumGlobalElements. Should equal sum of MyGlobalElements, or set to -1 to compute automatically.
5. -5 Minimum global element index is less than index base.
6. -99 Internal Epetra_BlockMap error. Contact developer.

For robust code, Epetra_BlockMap constructor calls should be caught using the try {...} catch {...} mechanism. For example:

  try {

    Epetra_BlockMap * map = new Epetra_BlockMap(NumGlobalElements, ElementSize, IndexBase, Comm);
  }
  catch (int Error) {
    if (Error==-1) { // handle error }
    if (Error==-2) ...

Note

{ In the current implementation, Epetra_BlockMap is the base class for:

• Epetra_Map.
• Epetra_LocalBlockMap.

}

Constructor & Destructor Documentation

Epetra_BlockMap::Epetra_BlockMap	(	int	NumGlobalElements,
		int	ElementSize,
		int	IndexBase,
		const Epetra_Comm &	Comm
	)

Epetra_BlockMap constructor for a Epetra-defined uniform linear distribution of constant size elements.

Creates a map that distributes NumGlobalElements elements evenly across all processors in the Epetra_Comm communicator. If NumGlobalElements does not divide exactly into the number of processors, the first processors in the communicator get one extra element until the remainder is gone.

The elements are defined to have a constant fixed size specified by ElementSize.

Parameters

In	NumGlobalElements - Number of elements to distribute.
In	ElementSize - Number of points or vector entries per element.
In	IndexBase - Minimum index value used for arrays that use this map. Typically 0 for C/C++ and 1 for Fortran.
In	Comm - Epetra_Comm communicator containing information on the number of processors.

Returns

Pointer to a Epetra_BlockMap object.

Epetra_BlockMap::Epetra_BlockMap	(	int	NumGlobalElements,
		int	NumMyElements,
		int	ElementSize,
		int	IndexBase,
		const Epetra_Comm &	Comm
	)

Epetra_BlockMap constructor for a user-defined linear distribution of constant size elements.

Creates a map that puts NumMyElements on the calling processor. If NumGlobalElements=-1, the number of global elements will be the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.

The elements are defined to have a constant fixed size specified by ElementSize.

Parameters

In	NumGlobalElements - Number of elements to distribute. Must be either -1 or equal to the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.
In	NumMyElements - Number of elements owned by the calling processor.
In	ElementSize - Number of points or vector entries per element.
In	IndexBase - Minimum index value used for arrays that use this map. Typically 0 for C/C++ and 1 for Fortran.
In	Comm - Epetra_Comm communicator containing information on the number of processors.

Returns

Pointer to a Epetra_BlockMap object.

Epetra_BlockMap::Epetra_BlockMap	(	int	NumGlobalElements,
		int	NumMyElements,
		const int *	MyGlobalElements,
		int	ElementSize,
		int	IndexBase,
		const Epetra_Comm &	Comm
	)

Epetra_BlockMap constructor for a user-defined arbitrary distribution of constant size elements.

Creates a map that puts NumMyElements on the calling processor. The indices of the elements are determined from the list MyGlobalElements. If NumGlobalElements=-1, the number of global elements will be the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.

The elements are defined to have a constant fixed size specified by ElementSize.

Parameters

In	NumGlobalElements - Number of elements to distribute. Must be either -1 or equal to the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.
In	NumMyElements - Number of elements owned by the calling processor.
In	MyGlobalElements - Integer array of length NumMyElements. The ith entry contains the global index value of the ith element on this processor. Index values are not required to be contiguous on a processor, or to be within the range of 0 to NumGlobalElements. As long as the index values are consistently defined and used, any set of NumGlobalElements distinct integer values is acceptable.
In	ElementSize - Number of points or vector entries per element.
In	IndexBase - Minimum index value used for arrays that use this map. Typically 0 for C/C++ and 1 for Fortran.
In	Comm - Epetra_Comm communicator containing information on the number of processors.

Returns

Pointer to a Epetra_BlockMap object.

Epetra_BlockMap::Epetra_BlockMap	(	int	NumGlobalElements,
		int	NumMyElements,
		const int *	MyGlobalElements,
		const int *	ElementSizeList,
		int	IndexBase,
		const Epetra_Comm &	Comm
	)

Epetra_BlockMap constructor for a user-defined arbitrary distribution of variable size elements.

Creates a map that puts NumMyElements on the calling processor. If NumGlobalElements=-1, the number of global elements will be the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.

The elements are defined to have a variable size defined by ElementSizeList.

Parameters

In	NumGlobalElements - Number of elements to distribute. Must be either -1 or equal to the computed sum of NumMyElements across all processors in the Epetra_Comm communicator.
In	NumMyElements - Number of elements owned by the calling processor.
In	MyGlobalElements - Integer array of length NumMyElements. The ith entry contains the global index value of the ith element on this processor. Index values are not required to be contiguous on a processor, or to be within the range of 0 to NumGlobalElements. As long as the index values are consistently defined and used, any set of NumGlobalElements distinct integer values is acceptable.
In	ElementSizeList - A list of the element sizes for elements owned by the calling processor. The ith entry contains the element size of the ith element on this processor.
In	IndexBase - Minimum index value used for arrays that use this map. Typically 0 for C/C++ and 1 for Fortran.
In	Comm - Epetra_Comm communicator containing information on the number of processors.

Returns

Pointer to a Epetra_BlockMap object.

Epetra_BlockMap::Epetra_BlockMap	(	long long	NumGlobal_Elements,
		int	NumMy_Elements,
		const long long *	myGlobalElements,
		int	ElementSize,
		int	indexBase,
		const Epetra_Comm &	comm,
		bool	UserIsDistributedGlobal,
		long long	UserMinAllGID,
		long long	UserMaxAllGID
	)

Epetra_BlockMap constructor for a user-defined arbitrary distribution of constant size elements, where the user provides all the globals.

Warning

This method is intended for expert developer use only, and should never be called by user code.

Member Function Documentation

const Epetra_BlockMapData* Epetra_BlockMap::DataPtr ( ) const

inline

Returns a pointer to the BlockMapData instance this BlockMap uses.

(Intended for developer use only for testing purposes.)

int Epetra_BlockMap::FirstPointInElement

(

int

LID

)

const

Returns the requested entry in the FirstPointInElementList; see FirstPointInElementList() for details.

This function provides similar functionality to FirstPointInElementList(), but for simple maps may avoid the explicit construction of the FirstPointInElementList array. Returns -1 if LID is out-of-range.

int* Epetra_BlockMap::FirstPointInElementList

(

)

const

Pointer to internal array containing a mapping between the local elements and the first local point number in each element.

This array is a scan sum of the ElementSizeList such that the ith entry in FirstPointInElementList is the sum of the first i-1 entries of ElementSizeList().

bool Epetra_BlockMap::PointSameAs

(

const Epetra_BlockMap &

Map

)

const

Returns true if this and Map have identical point-wise structure.

If both maps have the same number of global points and the same point distribution across processors then this method returns true.

int Epetra_BlockMap::ReferenceCount ( ) const

inline

Returns the reference count of BlockMapData.

(Intended for testing purposes.)

int Epetra_BlockMap::RemoteIDList ( int  NumIDs, const int *  GIDList, int *  PIDList, int *  LIDList  ) const

inline

Returns the processor IDs and corresponding local index value for a given list of global indices.

For each element (GID) of a given list of global element numbers (stored in GIDList) of length NumIDs, this function returns (in PIDList) the ID (rank) of the processor that owns the GID for this map and returns the local index (in LIDList) of the GID on that processor.

If a GID is present on more than one processor, the lowest rank processor ID is used, as is the LID for that processor. If a GID is not present on any processor, the corresponding PID will return as -1.

int Epetra_BlockMap::RemoteIDList	(	int	NumIDs,
		const int *	GIDList,
		int *	PIDList,
		int *	LIDList,
		int *	SizeList
	)		const

Returns the processor IDs, corresponding local index value, and element size for a given list of global indices.

For each element (GID) of a given a list of global element numbers (stored in GIDList) of length NumIDs, this function returns (in PIDList) the with processor that owns the GID for this map and returns the local index (in LIDList) of the GID on that processor. Finally it returns the element sizes in SizeList.

Epetra_BlockMap* Epetra_BlockMap::RemoveEmptyProcesses

(

)

const

Return a new BlockMap with processes with zero elements removed.

Warning

This method is only for expert users. Understanding how to use this method correctly requires some familiarity with semantics of MPI communicators.

We make no promises of backwards compatibility for this method. It may go away or change at any time.

This method first computes a new communicator, which contains only those processes in this Map's communicator (the "original communicator") that have a nonzero number of elements in this BlockMap (the "original BlockMap"). It then returns a new BlockMap distributed over the new communicator. The new BlockMap represents the same distribution as the original BlockMap, except that processes containing zero elements are not included in the new BlockMap or its communicator. On processes not included in the new BlockMap or communicator, this method returns NULL.

The returned BlockMap always has a distinct communicator from this BlockMap's original communicator. The new communicator contains a subset of processes from the original communicator. Even if the number of processes in the new communicator equals the number of processes in the original communicator, the new communicator is distinct. (In an MPI implementation, the new communicator is created using MPI_Comm_split.)

This method must be called collectively on the original communicator. It leaves the original Map and communicator unchanged.

This method was intended for applications such as algebraic multigrid or other multilevel preconditioners. Construction of each level of the multilevel preconditioner typically requires constructing sparse matrices, which in turn requires all-reduces over all participating processes at that level. Matrix sizes at successively coarser levels shrink geometrically. At the coarsest levels, some processes might be left with zero rows of the matrix, or the multigrid implementation might "rebalance" (redistribute the matrix) and intentionally leave some processes with zero rows. Removing processes with zero rows makes the all-reduces and other communication operations cheaper.

Epetra_BlockMap* Epetra_BlockMap::ReplaceCommWithSubset

(

const Epetra_Comm *

Comm

)

const

Replace this BlockMap's communicator with a subset communicator.

Warning

This method is only for expert users. Understanding how to use this method correctly requires some familiarity with semantics of MPI communicators.

We make no promises of backwards compatibility for this method. It may go away or change at any time.

Precondition

The input communicator's processes are a subset of this BlockMap's current communicator's processes.

On processes which are not included in the input communicator, the input communicator is null.

This method must be called collectively on the original communicator. It leaves the original BlockMap and communicator unchanged.

Note

This method differs from removeEmptyProcesses(), in that it does not assume that excluded processes have zero entries. For example, one might wish to remove empty processes from the row BlockMap of a CrsGraph using removeEmptyProcesses(), and then apply the resulting subset communicator to the column, domain, and range Maps of the same graph. For the latter three Maps, one would in general use this method instead of removeEmptyProcesses(), giving the new row BlockMap's communicator to this method.

bool Epetra_BlockMap::SameBlockMapDataAs

(

const Epetra_BlockMap &

Map

)

const

Returns true if maps share same block map data underneath. This is a very cheap check whether two maps are identical.

bool Epetra_BlockMap::UniqueGIDs ( ) const

inline

Returns true if map GIDs are 1-to-1.

Certain operations involving Epetra_BlockMap and Epetra_Map objects are well-defined only if the map GIDs are uniquely present in the map. In other words, if a GID occurs in the map, it occurs only once on a single processor and nowhere else. This boolean test returns true if this property is true, otherwise it returns false.

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The documentation for this class was generated from the following file:

• Epetra_BlockMap.h