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 PETSC_NULL scatters all values)
	iy	- the indices of yin to hold results (if PETSC_NULL fills entire vector yin)

Output Parameter

newctx -location to store the new scatter context

Options Database Keys

	-vecscatter_merge	- VecScatterBegin() handles all of the communication, VecScatterEnd() is a nop eliminates the chance for overlap of computation and communication
	-vecscatter_ssend	- Uses MPI_Ssend_init() instead of MPI_Send_init()
	-vecscatter_sendfirst	- Posts sends before receives
	-vecscatter_rr	- use ready receiver mode for MPI sends
	-vecscatter_packtogether	- Pack all messages before sending, receive all messages before unpacking ONLY implemented for BLOCK SIZE of 4 and 12! (others easily added)

C++ variants

VecScatter VecScatterCreate(Vec x,Vec y,IS is)	->	VecScatterCreate(x,PETSC_NULL,y,is,&s); return s;
VecScatterCreate(Vec x,Vec y,IS is,VecScatter *s)	->	VecScatterCreate(x,PETSC_NULL,y,is,s)
VecScatter VecScatterCreate(Vec x,IS is,Vec y)	->	VecScatterCreate(x,is,y,PETSC_NULL,&s); return s;
VecScatterCreate(Vec x,IS is,Vec y,VecScatter *s)	->	VecScatterCreate(x,is,y,PETSC_NULL,s)
VecScatter VecScatterCreate(Vec x,IS is1,Vec y,IS is2)	->	VecScatterCreate(x,is1,y,is2,&s); return s;

Notes

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.

Examples

src/dm/ao/examples/tutorials/ex2.c.html
src/dm/da/examples/tutorials/ex6.c.html
src/dm/da/examples/tutorials/ex6f90.F.html