petsc-3.9.4 2018-09-11

VecStrideNorm

Computes the norm of subvector of a vector defined by a starting point and a stride.

#include "petscvec.h" 
PetscErrorCode  VecStrideNorm(Vec v,PetscInt start,NormType ntype,PetscReal *nrm)

Collective on Vec

	v	- the vector
	start	- starting point of the subvector (defined by a stride)
	ntype	- type of norm, one of NORM_1, NORM_2, NORM_INFINITY

norm -the norm

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 computes the norm of the array (x[start],x[start+stride],x[start+2*stride], ....)

This is useful for computing, say the norm of the pressure variable when the pressure is stored (interlaced) with other variables, say density etc.

This will only work if the desire subvector is a stride subvector

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