How to coarse my grid
 

Dear friends, I'm facing a problem and I hope somebody can help me. I have a grid and I need to coarse it during my computation as if I had to run a sort of multigrid algorithm. I 'd like to coarse my grid, reducing the number of cell of 5-10 times, creating bigger elements (all bigger tetrahedra may be OK). Anybody can suggest me a library dedicated in grid coarsening? Thank you so much for your attention.Luca