Re: [Libmesh-devel] Moving nodes...

[Derek G. <fri...@gm...>]

It turns out that the call to prepare_for_use was unnecessary.... somewhere
along the line I screwed up my cause and effect ;-)

I do get negative Jacobians sometimes.... well... I don't think they're
actually negative as much as they are possibly -0...

It happens when the smoother pushes points too close together... which is of
course not good, but that's what I'm working on....

I thought I was getting this error prematurely, but it looks like I
wasn't... so false alarm...

Thanks for the reply,
Derek

On 6/7/06, Roy Stogner <roy...@ic...> wrote:
>
> On Tue, 6 Jun 2006, Derek Gaston wrote:
>
> > So I've implemented Larisa's smoother inside libmesh (well... I've
> > shoehorned her code into a mesh_smoother based class and hooked
> everything
> > up so it works... there is still a _lot_ of improvement left to be done)
> and
> > now I'm trying to use it... I was trying to use it in mid-iteration
> during
> > an explicit solve (modified example10)... and after doing the smooth I
> was
> > getting an error of:
> >
> > ERROR: negative Jacobian!
> > [0] src/fe/fe_map.C, line 312, compiled Jun  5 2006 at 20:27:59
> >
> > After thinking about it for a while I decided to run
> mesh.prepare_for_use().
> > This seems to work.... but I'm kind of in the dark as to why.  What is
> it
> > about moving the mesh nodes that needs prepare_for_use?  Further, is
> this
> > really what I should be doing, or is there another function I should be
> > using instead?
>
> If you just change the node positions, then it's of course possible to
> accidentally invert an element and get a negative Jacobian error from
> fe_map.C... but there shouldn't be anything that prepare_for_use()
> does that would affect that.
>
> Have you run this through the debugger yet, to see why you're getting
> a negative Jacobian on one of your elements?
> ---
> Roy
>