IndexMap Class Reference

This class represents the distribution index arrays across processes. An index array is a contiguous collection of N+1 indices [0, 1, . . ., N] that are distributed across M processes. On a given process, the IndexMap stores a portion of the index set using local indices [0, 1, . . . , n], and a map from the local indices to a unique global index. More...

#include <IndexMap.h>

Public Member Functions
	IndexMap (MPI_Comm comm, std::int32_t local_size)
	Create an non-overlapping index map.
	IndexMap (MPI_Comm comm, std::int32_t local_size, std::span< const std::int64_t > ghosts, std::span< const int > owners)
	Create an overlapping (ghosted) index map.
	IndexMap (MPI_Comm comm, std::int32_t local_size, const std::array< std::vector< int >, 2 > &src_dest, std::span< const std::int64_t > ghosts, std::span< const int > owners)
	Create an overlapping (ghosted) index map.
	IndexMap (const IndexMap &map)=delete
	IndexMap (IndexMap &&map)=default
	Move constructor.
	~IndexMap ()=default
	Destructor.
IndexMap &	operator= (IndexMap &&map)=default
	Move assignment.
IndexMap &	operator= (const IndexMap &map)=delete
std::array< std::int64_t, 2 >	local_range () const noexcept
	Range of indices (global) owned by this process.
std::int32_t	num_ghosts () const noexcept
	Number of ghost indices on this process.
std::int32_t	size_local () const noexcept
	Number of indices owned by this process.
std::int64_t	size_global () const noexcept
	Number indices across communicator.
const std::vector< std::int64_t > &	ghosts () const noexcept
	Local-to-global map for ghosts (local indexing beyond end of local range)
MPI_Comm	comm () const
	Return the MPI communicator that the map is defined on.
void	local_to_global (std::span< const std::int32_t > local, std::span< std::int64_t > global) const
	Compute global indices for array of local indices.
void	global_to_local (std::span< const std::int64_t > global, std::span< std::int32_t > local) const
	Compute local indices for array of global indices.
std::vector< std::int64_t >	global_indices () const
	Build list of indices with global indexing.
const std::vector< int > &	owners () const
	The ranks that own each ghost index.
std::pair< IndexMap, std::vector< std::int32_t > >	create_submap (std::span< const std::int32_t > indices) const
	Create new index map from a subset of indices in this index map.
graph::AdjacencyList< int >	index_to_dest_ranks () const
	Compute map from each local (owned) index to the set of ranks that have the index as a ghost.
std::vector< std::int32_t >	shared_indices () const
	Build a list of owned indices that are ghosted by another rank.
const std::vector< int > &	src () const noexcept
	Ordered set of MPI ranks that own caller's ghost indices.
const std::vector< int > &	dest () const noexcept
	Ordered set of MPI ranks that ghost indices owned by caller.
bool	overlapped () const noexcept
	Check if index map has overlaps (ghosts on any rank).
std::array< double, 2 >	imbalance () const
	Returns the imbalance of the current IndexMap.

Detailed Description

This class represents the distribution index arrays across processes. An index array is a contiguous collection of N+1 indices [0, 1, . . ., N] that are distributed across M processes. On a given process, the IndexMap stores a portion of the index set using local indices [0, 1, . . . , n], and a map from the local indices to a unique global index.

Constructor & Destructor Documentation

IndexMap() [1/3]

IndexMap	(	MPI_Comm	comm,
		std::int32_t	local_size
	)

Create an non-overlapping index map.

Note

Collective

Parameters

[in]	comm	The MPI communicator
[in]	local_size	Local size of the index map, i.e. the number of owned entries

IndexMap() [2/3]

IndexMap	(	MPI_Comm	comm,
		std::int32_t	local_size,
		std::span< const std::int64_t >	ghosts,
		std::span< const int >	owners
	)

Create an overlapping (ghosted) index map.

This constructor uses a 'consensus' algorithm to determine the ranks that ghost indices that are owned by the caller. This requires non-trivial MPI communication. If the ranks that ghost indices owned by the caller are known, it more efficient to use the constructor that takes these ranks as an argument.

Note

Collective

Parameters

[in]	comm	The MPI communicator
[in]	local_size	Local size of the index map, i.e. the number of owned entries
[in]	ghosts	The global indices of ghost entries
[in]	owners	Owner rank (on global communicator) of each entry in ghosts

IndexMap() [3/3]

IndexMap	(	MPI_Comm	comm,
		std::int32_t	local_size,
		const std::array< std::vector< int >, 2 > &	src_dest,
		std::span< const std::int64_t >	ghosts,
		std::span< const int >	owners
	)

Create an overlapping (ghosted) index map.

This constructor is optimised for the case where the 'source' (ranks that own indices ghosted by the caller) and 'destination' ranks (ranks that ghost indices owned by the caller) are already available. It allows the complex computation of the destination ranks from owners.

Note

Collective

Parameters

[in]	comm	The MPI communicator
[in]	local_size	Local size of the index map, i.e. the number
[in]	src_dest	Lists of [0] src and [1] dest ranks. The list in each must be sorted and not contain duplicates. src ranks are owners of the indices in ghosts. dest ranks are the rank that ghost indices owned by the caller.
[in]	ghosts	The global indices of ghost entries
[in]	owners	Owner rank (on global communicator) of each entry in ghosts

Member Function Documentation

comm()

MPI_Comm comm

(

)

const

Return the MPI communicator that the map is defined on.

Returns

Communicator

create_submap()

std::pair< IndexMap, std::vector< std::int32_t > > create_submap

(

std::span< const std::int32_t >

indices

)

const

Create new index map from a subset of indices in this index map.

The order of the owned indices is preserved, with new map effectively a 'compressed' map.

Parameters

[in]

indices

Local indices in the map that should appear in the new index map. All indices must be owned, i.e. indices must be less than this->size_local().

Precondition

indices must be sorted and contain no duplicates.

Returns

The (i) new index map and (ii) a map from the ghost position in the new map to the ghost position in the original (this) map

dest()

const std::vector< int > & dest ( ) const

noexcept

Ordered set of MPI ranks that ghost indices owned by caller.

Typically used when creating neighbourhood communicators.

Returns

MPI ranks than own ghost indices. The ranks are unique and sorted.

global_indices()

std::vector< std::int64_t > global_indices

(

)

const

Build list of indices with global indexing.

Returns

The global index for all local indices (0, 1, 2, ...) on this process, including ghosts

global_to_local()

void global_to_local	(	std::span< const std::int64_t >	global,
		std::span< std::int32_t >	local
	)		const

Compute local indices for array of global indices.

Parameters

[in]	global	Global indices
[out]	local	The local of the corresponding global index in 'global'. Returns -1 if the local index does not exist on this process.

imbalance()

std::array< double, 2 > imbalance

(

)

const

Returns the imbalance of the current IndexMap.

The imbalance is a measure of load balancing across all processes, defined as the maximum number of indices on any process divided by the average number of indices per process. This function calculates the imbalance separately for owned indices and ghost indices and returns them as a std::array<double, 2>. If the total number of owned or ghost indices is zero, the respective entry in the array is set to -1.

Note

This is a collective operation and must be called by all processes in the communicator associated with the IndexMap.

Returns

An array containing the imbalance in owned indices (first element) and the imbalance in ghost indices (second element).

index_to_dest_ranks()

graph::AdjacencyList< int > index_to_dest_ranks

(

)

const

Compute map from each local (owned) index to the set of ranks that have the index as a ghost.

Todo:

Aim to remove this function?

Returns

shared indices

local_to_global()

void local_to_global	(	std::span< const std::int32_t >	local,
		std::span< std::int64_t >	global
	)		const

Compute global indices for array of local indices.

Parameters

[in]	local	Local indices
[out]	global	The global indices

overlapped()

bool overlapped ( ) const

noexcept

Check if index map has overlaps (ghosts on any rank).

The return value of this function is determined by which constructor was used to create the index map.

Returns

True if index map has overlaps on any ranks, otherwise false.

owners()

const std::vector< int > & owners ( ) const

inline

The ranks that own each ghost index.

Returns

List of ghost owners. The owning rank of the ith ghost index is owners()[i].

shared_indices()

std::vector< std::int32_t > shared_indices

(

)

const

Build a list of owned indices that are ghosted by another rank.

Returns

The local index of owned indices that are ghosts on other rank(s). The indices are unique and sorted.

src()

const std::vector< int > & src ( ) const

noexcept

Ordered set of MPI ranks that own caller's ghost indices.

Typically used when creating neighbourhood communicators.

Returns

MPI ranks than own ghost indices. The ranks are unique and sorted.

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

• /__w/dolfinx/dolfinx/cpp/dolfinx/common/IndexMap.h
• /__w/dolfinx/dolfinx/cpp/dolfinx/common/IndexMap.cpp