[petsc-users] reusing LU factorization?

[David Liu]

True, also I should have read Chapter 4 of the manual before asking the
question. I will try the various options there and see if I get any
improvement.

One thing I'm very confused about though: as I mentioned in the first post,
I am solving the matrix multiple times and changing the elements, but not
the nonzero structure in between solves. We've established that the
numerical LU is done on the first solve only. Also, I forgot to mention
that I am *not* calling KSPSetOperator before the subsequent solves, which
is why the subsequent solves are so fast.

According to section 4.2 of the manual, this is actually not allowed if I
change anything about the matrix (which I am doing since I didn't know
about this). Then why are my solves still getting the correct results that
I am expecting?


On Wed, Jan 29, 2014 at 4:54 PM, Jed Brown <jed at jedbrown.org> wrote:

> David Liu <daveliu at mit.edu> writes:
> > Not too sure if there's anything I can do about this. Also, I am
> definately
> > willing to use other preconditioners. If direct solvers are expensive,
> what
> > are the cheaper alternatives?
>
> This is a vast question, a bit like asking what kind of "math" is
> important for "physics".  If you want help, you'll have to explain more
> about your problem, discretization, and regime.
>
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