exchange.hpp File Reference

MPI exchange operations for SparseVector. More...

#include <mpi.h>
#include <vector>
#include <openpfc/core/backend_tags.hpp>
#include <openpfc/core/sparse_vector.hpp>

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Functions
template<typename T >
MPI_Datatype	pfc::exchange::detail::get_mpi_type ()
	Get MPI datatype for type T.
template<>
MPI_Datatype	pfc::exchange::detail::get_mpi_type< double > ()
template<>
MPI_Datatype	pfc::exchange::detail::get_mpi_type< float > ()
template<>
MPI_Datatype	pfc::exchange::detail::get_mpi_type< int > ()
template<>
MPI_Datatype	pfc::exchange::detail::get_mpi_type< size_t > ()
template<typename BackendTag , typename T >
void	pfc::exchange::send (const core::SparseVector< BackendTag, T > &sparse_vector, int sender_rank, int receiver_rank, MPI_Comm comm, int tag=0)
	Send SparseVector (both indices and data) - setup phase.
template<typename BackendTag , typename T >
void	pfc::exchange::receive (core::SparseVector< BackendTag, T > &sparse_vector, int sender_rank, int receiver_rank, MPI_Comm comm, int tag=0)
	Receive SparseVector (both indices and data) - setup phase.
template<typename BackendTag , typename T >
void	pfc::exchange::send_data (const core::SparseVector< BackendTag, T > &sparse_vector, int sender_rank, int receiver_rank, MPI_Comm comm, int tag=0)
	Send only data values (indices already known) - runtime phase.
template<typename BackendTag , typename T >
void	pfc::exchange::receive_data (core::SparseVector< BackendTag, T > &sparse_vector, int sender_rank, int receiver_rank, MPI_Comm comm, int tag=0)
	Receive only data values (indices already known) - runtime phase.

Detailed Description

MPI exchange operations for SparseVector.

Provides two-phase exchange for SparseVector:

1. Setup phase (expensive, done once):
   • send(sparse_vec, sender_rank, receiver_rank, comm): Sends both indices and data
   • receive(sparse_vec, sender_rank, receiver_rank, comm): Receives both indices and data
2. Runtime phase (cheap, done every step):
   • send_data(sparse_vec, sender_rank, receiver_rank, comm): Sends only data values
   • receive_data(sparse_vec, sender_rank, receiver_rank, comm): Receives only data values

Key optimization: Indices are exchanged once, then only values are transferred.

// Setup: Exchange indices once
auto sparse = sparsevector::create<double>({0, 2, 4});
exchange::send(sparse, my_rank, neighbor_rank, MPI_COMM_WORLD);
exchange::receive(sparse, neighbor_rank, my_rank, MPI_COMM_WORLD);
 
// Runtime: Exchange only values (repeatedly)
for (int step = 0; step < 1000; ++step) {
  exchange::send_data(sparse, my_rank, neighbor_rank, MPI_COMM_WORLD);
  exchange::receive_data(sparse, neighbor_rank, my_rank, MPI_COMM_WORLD);
}

See also

core/sparse_vector.hpp for SparseVector definition

Author

OpenPFC Development Team

Date

2025

Function Documentation

receive()

template<typename BackendTag , typename T >

void pfc::exchange::receive	(	core::SparseVector< BackendTag, T > &	sparse_vector,
		int	sender_rank,
		int	receiver_rank,
		MPI_Comm	comm,
		int	tag = 0
	)

Receive SparseVector (both indices and data) - setup phase.

Receives both indices and data from sender. Used during initialization.

Parameters

sparse_vector	SparseVector to receive into (will be resized)
sender_rank	MPI rank of sender
receiver_rank	MPI rank of receiver
comm	MPI communicator
tag	MPI message tag (default: 0)

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receive_data()

template<typename BackendTag , typename T >

void pfc::exchange::receive_data	(	core::SparseVector< BackendTag, T > &	sparse_vector,
		int	sender_rank,
		int	receiver_rank,
		MPI_Comm	comm,
		int	tag = 0
	)

Receive only data values (indices already known) - runtime phase.

Receives only the data values, assuming indices are already set. Much cheaper than full receive.

Parameters

sparse_vector	SparseVector to receive data into
sender_rank	MPI rank of sender
receiver_rank	MPI rank of receiver
comm	MPI communicator
tag	MPI message tag (default: 0)

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send()

template<typename BackendTag , typename T >

void pfc::exchange::send	(	const core::SparseVector< BackendTag, T > &	sparse_vector,
		int	sender_rank,
		int	receiver_rank,
		MPI_Comm	comm,
		int	tag = 0
	)

Send SparseVector (both indices and data) - setup phase.

Sends both indices and data to receiver. Used during initialization to establish communication pattern.

Parameters

sparse_vector	SparseVector to send
sender_rank	MPI rank of sender
receiver_rank	MPI rank of receiver
comm	MPI communicator
tag	MPI message tag (default: 0)

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send_data()

template<typename BackendTag , typename T >

void pfc::exchange::send_data	(	const core::SparseVector< BackendTag, T > &	sparse_vector,
		int	sender_rank,
		int	receiver_rank,
		MPI_Comm	comm,
		int	tag = 0
	)

Send only data values (indices already known) - runtime phase.

Sends only the data values, assuming receiver already knows the indices. Much cheaper than full send.

Parameters

sparse_vector	SparseVector to send data from
sender_rank	MPI rank of sender
receiver_rank	MPI rank of receiver
comm	MPI communicator
tag	MPI message tag (default: 0)

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