[petsc-users] Questions about AMG and Jacobian Contruction

[Yingjie Wu]

Respected PETSc developers:
Hi,
I have some questions about some functions of AMG and the construction time
of Jacobian matrix in the process of using. Please help me to answer them.

1. I see some functions about AMG in the list of PETSc functions. I wonder
if DMDA is necessary to construct vectors when using AMG precondition.
(Because the geometry described in my PDE is irregular,it contains a lot of
pipes and connections, instead of using DMDA to manage vectors, I define
discrete solution vectors by myself.)

2. As far as I know, besides V-cycle, AMG method also needs auxiliary
matrix B and transfer matrix P (transfer matrix from fine mesh to coarse
mesh). Are these transformation matrices built-in or can they be provided
by users in PETSc?

3. At present, in my program, I use -snes_mf_operator to solve the
non-linear PDE problem. Although I do not directly construct Jacobian
matrix, it is also expensive to construct preconditioning matrix (provided
by users). Can I control the update and decomposition time of the
preconditioning matrix, such as updating the preconditioning matrix every
two Newton steps and then ILU factorization? Can these controls be
implemented in SNESMonitor?

Thanks,
Yingjie
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