Direct preconditioners

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1

Dear NGSolve community,

up until now, I have been preconditioning my iterative solvers mainly with
BDDC and Block GS methods and wonder, whether there is an ILU directly available in NGSolve.
(I know, I could possibly use PETSc for this.)
I have read about the “direct preconditioner” in your tutorial, but reading the C++ code I cannot
see that, e.g., PARDISO is configured differently as preconditioner than being employed as
direct solver.
Did I miss something or means using a “direct preconditioner” that a direct solver is employed and
I refine the result afterwards with an iterative method, or are the direct solvers providing an ILU?

Best regards,
Philipp

2

Hi Philipp,

There is no ILU directly in NGSolve. As you said, your best option is probably to use PETSc.

The “direct preconditioner” is the exact inverse, it is just packaged into a “preconditioner” so you can switch between direct solvers and preconditioners
easily.

Best, Lukas

3

Thanks for the clarification!

Best,
Philipp