[petsc-users] Jacobian check is sensitive to the choice of differencing parameter

[Khai Pham]

Dear Petsc-Users,

The SNES only converges for a small problem. I did the jacobian check. The
result is sensitive to the choice of differencing parameter.

With the option "-snes_type test":

"Norm of matrix ratio 4.11569e-09 difference 7.64426e-07 (user-defined
state)
Norm of matrix ratio 2.05846e-08 difference 3.89655e-06 (constant state
-1.0)
Norm of matrix ratio 5.77446e-09 difference 1.09307e-06 (constant state
1.0)"

with the option "-snes_type test -mat_fd_type ds" :

"Norm of matrix ratio 1.05213e-07 difference 1.95418e-05 (user-defined
state)
Norm of matrix ratio 2.51463e-07 difference 4.76004e-05 (constant state
-1.0)
Norm of matrix ratio 2.81081e-08 difference 5.32071e-06 (constant state
1.0)".

Could you give me any hint where should I check for the error?

Khai
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