[petsc-users] a question about DAE Function

[Jed Brown]

"Jin, Shuangshuang" <Shuangshuang.Jin at pnnl.gov> writes:

> Hi, thanks for your message, but I still have a few questions here.
>
> 1. How to "reuse the VecScatter"?

Store it in your user context and reuse it the next time you need to scatter.

> 2. The data movement of O(N) is for scattering X vector to each
> processor? And the computation of O(N^3) is for solving the DAE
> equation in parallel? So "the parallelism will be useful if N is large
> enough" as you indicated. Then does that mean my current
> implementation of scattering X and defining f[] on different
> processors to solve the DAE in parallel is the right way to do it?
> Then what's the benefit of using MatElemental?

That's fine to define the equations, but you still have to solve them
somehow.  Most common methods do that using a matrix.

> 3. When I looked into the example of MatElemental, it seems to me that
> they're all matrix operations. I cannot understand its connection with
> my code, especially the IFUNCTION part. I only have several functions
> definitions f[] using the data of a distributed array X. Don't know
> where and how to use MatElemental here.

Are you assembling a Jacobian (TSSetIJacobian)?  If not, then Elemental
will not help, but keep in mind that this will converge very slowly
unless your system is well-conditioned.