Re: [Libmesh-users] about the long time for the assemble of first step!

[Roy S. <ro...@st...>]

On Tue, 13 May 2008, luyi wrote:

> The CONSTANT basis for both implicit and RK is OK but higher order need
> much more time because
>
> I use elem-based basis, maybe the problem is this?

You're probably just not getting the correct sparsity pattern
preallocation because libMesh isn't expecting you to be doing a DG
method, and so isn't expecting direct coupling between the elem-based
DoFs in neighboring elements.  I'm surprised CONSTANT worked okay if
that's the problem, though, unless we have some half-working
autodetection code in there that I don't know about.

But my important quesiton:

Did you try Ben's command line option suggestion yet?  There ought to
be a better way to autodetect DG-like DoF coupling, but unless we do a
"fake" system assembly on a two-element mesh, I don't see how to make
it seamless.  For now, the problem is probably just "you need to
explicitly tell libMesh you're doing DG".

> Thank you very much and Best regards!

If you're feeling especially grateful, you might think about
contributing a simple DG libMesh example once your own code is
straightened out.  All the main developers are pretty swamped right
now, but that's something we've needed for a while.
---
Roy