[petsc-users] Understanding 'snes' object

[Stefano Zampini]

Il giorno sab 23 ago 2025 alle ore 00:25 Zou, Ling via petsc-users <
petsc-users at mcs.anl.gov> ha scritto:

> Hi all,
>
>
>
> Can someone please help me understand the output of the following two
> outputs using ‘-snes_view’?
>
>
>
> Option 1:
>
> SNES Object: 1 MPI process
>
>   type: newtonls
>
>   maximum iterations=15, maximum function evaluations=10000
>
>   tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
>
>   total number of linear solver iterations=5
>
>   total number of function evaluations=14
>
>   norm schedule ALWAYS
>
>   Jacobian is built using finite differences with coloring
>
>
>
> Option 2:
>
> SNES Object: 1 MPI process
>
>   type: newtonls
>
>   maximum iterations=50, maximum function evaluations=10000
>
>   tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
>
>   total number of linear solver iterations=8
>
>   total number of function evaluations=17
>
>   norm schedule ALWAYS
>
>   Jacobian is applied matrix-free with differencing
>
>   Preconditioning Jacobian is built using finite differences with coloring
>
>
>
>
>
> Does it mean that
>
>    - Option 1 uses Newton’s method, such that J du = b is solved with J
>    being explicitly constructed?
>
> yes


>
>    -
>    - Option 2 uses matrix free method, such that J du = b is solved with
>     J v ~ (F(u + dv) – F(u)) / h when needed, e.g., in a Krylov method.
>
>
yes, and the preconditioner is constructed using an explicitly constructed
Jacobian matrix


>
>    -
>
>
>
> Thanks,
>
> -Ling
>
>
>
>
>


-- 
Stefano
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