[petsc-users] Queries related to snes options

[Aman Saxena]

I am trying to use PETSc's TS to implement implicit time-stepping, for
1d-Euler Equation discretized using 5th order WENO schemes. I have
following queries related to using some of the snes options::

-- What does -ts_max_snes_failure means and what does the non-linear solver
do once it diverges to ensure convergence?

-- If I do not specify “-snes_fd” or “-snes_mf”, does by default it uses
the jacobian I have coded instead of building it using Finite-differences?

-- As “-snes_fd ” replaces my routine to calculate the jacobian with
petsc’s fd routine, does it stores the jacobian in the same Matrix that I
pass to my hand-coded routine. It might lead to some inconsistency as my
actual scheme involves stencils width equals 3 while I am approximating the
Jacobian using first order scheme which requires stencils width equals 1.
So I have used another “dmda” with sw = 1, to initialize the matrix using
“DMCreateMatrix()” while fd needs sw = 3.

-- I am not able to use “-snes_type test” it gives me the following error
“[0]PETSC ERROR: Unknown type. Check for miss-spelling or missing package:
http://www.mcs.anl.gov/petsc/documentation/installation.html#external
 [0]PETSC ERROR: Unable to find requested SNES type test”

-- What exactly "PCMAT" do? Do I have to supply matrix other than in
RHSJacobian for PCMAT?

Thanks
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