petsc-3.14.6 2021-03-30

VecStrideGather

Gathers a single component from a multi-component vector into another vector.

#include "petscvec.h" 
PetscErrorCode  VecStrideGather(Vec v,PetscInt start,Vec s,InsertMode addv)

Collective on Vec

	v	- the vector
	start	- starting point of the subvector (defined by a stride)
	addv	- one of ADD_VALUES,INSERT_VALUES,MAX_VALUES

- the location where the subvector is stored

One must call VecSetBlockSize() before this routine to set the stride information, or use a vector created from a multicomponent DMDA.

If x is the array representing the vector x then this gathers the array (x[start],x[start+stride],x[start+2*stride], ....)

The parallel layout of the vector and the subvector must be the same; i.e., nlocal of v = stride*(nlocal of s)

Not optimized; could be easily

advanced