VecNormAvailable#
Returns the vector norm if it is already known.
Synopsis#
#include "petscvec.h"
PetscErrorCode VecNormAvailable(Vec x, NormType type, PetscBool *available, PetscReal *val)
Not Collective
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 Parameters#
available - PETSC_TRUE if the val returned is valid
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|
Performance Issues#
per-processor memory bandwidth
interprocessor latency
work load imbalance that causes certain processes to arrive much earlier than others
Compile Option#
PETSC_HAVE_SLOW_BLAS_NORM2 will cause a C (loop unrolled) version of the norm to be used, rather than the BLAS. This should probably only be used when one is using the FORTRAN BLAS routines (as opposed to vendor provided) because the FORTRAN BLAS NRM2() routine is very slow.
See Also#
VecDot()
, VecTDot()
, VecNorm()
, VecDotBegin()
, VecDotEnd()
, VecNorm()
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