Re: [Libmesh-devel] help on errors in using Gmsh with libmesh

[John P. <jwp...@gm...>]

Hi Rochan,

>    n_dofs()=0
>    n_local_dofs()=0
>    n_constrained_dofs()=0
>    n_vectors()=1
>
> The mesh is read correctly. However, it does not display the number of
> degrees of freedom. I would surmise that given the mesh (a structured
> mesh with quadrilaterals) and the approximation order it ought to be
> able to tell the number of degrees of freedom.

This issue popped up a couple days ago in the context of the TetGen reader.

You have to call mesh.prepare_for_use() after reading in the mesh so
that it is properly partitioned; this should fix the n_dofs() problem


> In hte code, I only replaced the libMesh mesh generation in example 3
> with the line
> GmshIO(mesh).read("gmsh_ex3.msh");
>
> Further the above errors are with first order approximation. If I use
> second order:
>
>  equation_systems.get_system("Poisson").add_variable("u", SECOND);
>
> Then I receive the following error message:
>
> [0] src/fe/fe_lagrange.C, line 632, compiled Mar  2 2011 at 09:35:54
> terminate called after throwing an instance of 'libMesh::LogicError'
>  what():  Error in libMesh internal logic

Are these QUAD4's from GMSH?  You won't be able to use second-order
elements on QUAD4's, you can convert them to QUAD9's with a call to
mesh.all_second_order().

-- 
John