petsc-3.12.5 2020-03-29

VecScatterCreate

Creates a vector scatter context.

Synopsis

#include "petscvec.h"    
PetscErrorCode VecScatterCreate(Vec xin,IS ix,Vec yin,IS iy,VecScatter *newctx)

Collective on Vec

Input Parameters

	xin	- a vector that defines the shape (parallel data layout of the vector) of vectors from which we scatter
	yin	- a vector that defines the shape (parallel data layout of the vector) of vectors to which we scatter
	ix	- the indices of xin to scatter (if NULL scatters all values)
	iy	- the indices of yin to hold results (if NULL fills entire vector yin)

Output Parameter

newctx -location to store the new scatter context

Options Database Keys

-vecscatter_view -Prints detail of communications

-vecscatter_view ::ascii_info -Print less details about communication

-vecscatter_merge -VecScatterBegin() handles all of the communication, VecScatterEnd() is a nop eliminates the chance for overlap of computation and communication

-vecscatter_packtogether -Pack all messages before sending, receive all messages before unpacking will make the results of scatters deterministic when otherwise they are not (it may be slower also).

-vecscatter_type sf -Use the PetscSF implementation of vecscatter (Default). One can use PetscSF options to control the communication.

Notes

If both xin and yin are parallel, their communicator must be on the same set of processes, but their process order can be different. In calls to VecScatter() you can use different vectors than the xin and yin you used above; BUT they must have the same parallel data layout, for example, they could be obtained from VecDuplicate(). A VecScatter context CANNOT be used in two or more simultaneous scatters; that is you cannot call a second VecScatterBegin() with the same scatter context until the VecScatterEnd() has been called on the first VecScatterBegin(). In this case a separate VecScatter is needed for each concurrent scatter.

Currently the MPI_Send() use PERSISTENT versions. (this unfortunately requires that the same in and out arrays be used for each use, this is why we always need to pack the input into the work array before sending and unpack upon receiving instead of using MPI datatypes to avoid the packing/unpacking).

Both ix and iy cannot be NULL at the same time.

Use VecScatterCreateToAll() to create a vecscatter that copies an MPI vector to sequential vectors on all MPI ranks. Use VecScatterCreateToZero() to create a vecscatter that copies an MPI vector to a sequential vector on MPI rank 0. These special vecscatters have better performance than general ones.

Level

intermediate

VecScatterCreate

Synopsis

Input Parameters

Output Parameter

Options Database Keys

Notes

See Also

Level

Location

Examples

Implementations