On Fri, Mar 7, 2008 at 2:46 AM, Jan Biermann <[EMAIL PROTECTED]> wrote: > Hey all, > sorry in advance for bothering you with probably a stupid question but I > am just confused by the following problem: > > I performed a simulation using a mesh with infinite elements and all is > fine. then I want to do some post-processing (getting the solution on > several single points in the computational domain) but all of a sudden I > get an error from the compute_map() function saying "negative Jacobian". > First thing is that the simulation worked fine without errors so the > mesh should be ok. Furthermore, it makes a difference if I read the > simulation mesh for the post-processing (that I wrote during the > simulation after building the infinite elements) or if I read just the > fe-mesh and reconstruct the final mesh by building the IFE in the
Out of curiosity, what file format are we talking about here? xda? Sounds like the error is in reading a mesh that has IFEs, not one with FEs only. I don't have experience with either. > post-processing code (the result is the same mesh). The error then pops > up for different elements. When I dump on the screen all the values that > are computed for the jacobian in "compute_map()" I always get "nan" and Wait, you are getting NaN for *every* element until you eventually get a negative Jacobian? It sounds like the whole mesh may have trouble and not just one element. Any idea if the neg. Jacobian is coming from a regular geometric finite element or an infinite element? > all of a sudden a number other than "nan" is computed which is negative > and causes the error. But like I said, using the "read in" mesh a > certain element causes a "nan" (and hence, no error message) and the > same element causes a negative value and the error when the IFE are > build in the post-processing code. This all makes no sense to me. Sounds like it must be a problem with the post-processing code. Also, I'm curious how you know it is the "same" element both times. Same connectivity? Is it possible some of the nodes were renumbered? A common way for a negative Jacobian to pop up is for the order of two nodes in the connectivity list to be transposed, effectively inverting the element. > (especially why in general a Jacobian=nan is computed). > > I hope this was not too confusing and stupid. Definitely confusing, but we won't know if it's stupid until we find the bug :-) I am in agreement with Ben here, if possible could you see if you could reproduce the problem on a mesh with one or two elements? -John > Thanks in advance for your help, > > Jan > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Libmesh-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/libmesh-users > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
