[petsc-users] pcfieldsplit for a composite dm with multiple subfields

[Jed Brown]

Gideon Simpson <gideon.simpson at gmail.com> writes:

> Checking the Jacobian, this is a pretty standard output:
>
>       Testing hand-coded Jacobian, if the ratio is O(1.e-8), the hand-coded Jacobian is probably correct.
>     Finite difference Jacobian
>     Hand-coded Jacobian
>     Hand-coded minus finite difference Jacobian
>     6.08281e-10 = ||J - Jfd||//J|| 0.000151055  = ||J - Jfd||
>
>
> Things look favorable in terms of relative difference, but the absolute difference is a bit more suspect.

It likely just means you have big matrix entries (perhaps due to poor nondimensionalization/scaling).
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