petsc-master 2014-11-25
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SNESDefaultMatrixFreeSetParameters2

Sets the parameters for the approximation of matrix-vector products using finite differences.

Synopsis

#include "petscsnes.h"   
PetscErrorCode  SNESDefaultMatrixFreeSetParameters2(Mat mat,PetscReal error,PetscReal umin,PetscReal h)
      J(u)*a = [J(u+h*a) - J(u)]/h where

either the user sets h directly here, or this parameter is computed via

       h = error_rel*u'a/||a||^2                        if  |u'a| > umin*||a||_{1}
         = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2   else

Input Parameters

mat - the matrix
error_rel - relative error (should be set to the square root of the relative error in the function evaluations)
umin - minimum allowable u-value
h - differencing parameter

Notes

If the user sets the parameter h directly, then this value will be used instead of the default computation indicated above.

Keywords

SNES, matrix-free, parameters

See Also

MatCreateSNESMF()

Level:advanced
Location:
src/snes/interface/noise/snesmfj2.c
Index of all SNES routines
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Index of all manual pages