petsc-master 2015-08-31
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VecNorm

Computes the vector norm.

Synopsis

#include "petscvec.h"   
PetscErrorCode  VecNorm(Vec x,NormType type,PetscReal *val)
Collective on Vec

Input Parameters

x - the vector
type - one of NORM_1, NORM_2, NORM_INFINITY. Also available NORM_1_AND_2, which computes both norms and stores them in a two element array.

Output Parameter

val -the norm

Notes

    NORM_1 denotes sum_i |x_i|
    NORM_2 denotes sqrt(sum_i (x_i)^2)
    NORM_INFINITY denotes max_i |x_i|

For complex numbers NORM_1 will return the traditional 1 norm of the 2 norm of the complex numbers; that is the 1 norm of the absolutely values of the complex entries. In PETSc 3.6 and earlier releases it returned the 1 norm of the 1 norm of the complex entries (what is returned by the BLAS routine asum()). Both are valid norms but most people expect the former.

Performance Issues

   per-processor memory bandwidth
   interprocessor latency
   work load inbalance that causes certain processes to arrive much earlier than others

See Also

VecDot(), VecTDot(), VecNorm(), VecDotBegin(), VecDotEnd(), VecNormAvailable(),
VecNormBegin(), VecNormEnd()

Level:intermediate
Location:
src/vec/vec/interface/rvector.c
Index of all Vec routines
Table of Contents for all manual pages
Index of all manual pages

Examples

src/vec/vec/examples/tutorials/ex1.c.html
src/vec/vec/examples/tutorials/ex11.c.html
src/vec/vec/examples/tutorials/ex1f.F.html
src/vec/vec/examples/tutorials/ex1f90.F.html
src/vec/vec/examples/tutorials/ex11f.F.html
src/vec/vec/examples/tutorials/ex20f90.F90.html
src/mat/examples/tutorials/ex2.c.html
src/mat/examples/tutorials/ex9.c.html
src/dm/examples/tutorials/ex10.c.html
src/ksp/ksp/examples/tutorials/ex1.c.html
src/ksp/ksp/examples/tutorials/ex2.c.html