[petsc-users] Problem about Scaling

[Yingjie Wu]

Respected Petsc developers
Hi,
I am currently using SNES to solve some non-linear PDEs. The model is a
two-dimensional X-Y geometry. Because the magnitude of different physical
variables is too large, it is difficult to find the direction in Krylov
subspace, and the residual descends very slowly or even does not converge.
I think my PDEs need scaling. I need some help to solve the following
quentions.

1. I use - snes_mf_operator, so instead of providing Jacobian matrix, I
only set up an approximate Jacobian matrix for precondition. For my model,
do I just need to magnify the residuals to the same level? Is there any
need to modify the precondition matrix?
2. I have seen some articles referring to the non-dimensional method. I
don't know how to implement this method in the program and how difficult it
is to implement.

Thanks,
Yingjie
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