[Gmsh] [deal.II] Problems with gmsh 2D quad grids and deal.ii

[Wolfgang Bangerth]

> Of these 31 fail with the error message:
>
> The violated condition was:
> n_negative_cells==0 || n_negative_cells==cells.size()

This typically happens if you have inverted cells or cells that are not convex 
in your mesh. This would be a result of what gmsh outputs.

(The test verifies that either no cells are inverted, or all are. If all are, 
deal.II inverts all cells.)


> and 8 fail with the error message:
>
> The violated condition was:
>      needed_lines.find(std::make_pair(line_vertices.second,
>      line_vertices.first)) == needed_lines.end()

I don't know about this one (or the variant Mikhail posted -- thanks!). It 
would be useful to have an input file that triggers this.

Best
  W.

-- 
------------------------------------------------------------------------
Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/