PETSc version 3.15.5
MatMFFDSetFunctionError
Sets the error_rel for the approximation of matrix-vector products using finite differences. 
Synopsis
#include "petscmat.h"   
PetscErrorCode  MatMFFDSetFunctionError(Mat mat,PetscReal error)
Logically Collective on Mat
Input Parameters
|  | mat | - the matrix free matrix created via MatCreateMFFD() or MatCreateSNESMF() | 
|  | error_rel | - relative error (should be set to the square root of
the relative error in the function evaluations) | 
Options Database Keys
|  | -mat_mffd_err <error_rel> | - Sets error_rel | 
Notes
The default matrix-free matrix-vector product routine computes
     F'(u)*a = [F(u+h*a) - F(u)]/h where
     h = error_rel*u'a/||a||^2                        if  |u'a| > umin*||a||_{1}
       = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2   else
See Also
 MatCreateSNESMF(),MatMFFDGetH(), MatCreateMFFD(), MATMFFD
MatMFFDSetHHistory(), MatMFFDResetHHistory()
Level
advanced
Location
src/mat/impls/mffd/mffd.c
Implementations
MatMFFDSetFunctionError_MFFD in src/mat/impls/mffd/mffd.c
Index of all Mat routines
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