GRUMMP is quite successful in coarsening isotropic unstructured meshes -- nearly all vertices are removed in each case, and mesh quality is quite good. Two-dimensional anisotropic meshes are also handled well. The weakest area, by far, is anisotropic three-dimensional meshes, where the number of vertices that can not be removed climbs sharply, and mesh quality is poor (even allowing for anisotropy).

Two strategies that have some chance at success have not yet been investigated:

Carl Ollivier-Gooch 2017-07-20