Thèse de doctorat
Résumé : We give a 2-approximation algorithm for Cluster Vertex Deletion. This tight result matches the hardness lower bound. We obtain a new deterministic 7/3-approximation algorithm for Feedback Vertex Set in Tournaments. This result is based on the LP given by just one round of Sherali-Adams. We find a new, simpler deterministic (2 + epsilon)-approximation algorithm for Split Vertex Deletion. We give a 2-approximation algorithm for Claw-Free Vertex Deletion in triangle-free graphs. In the case of general graphs we prove that it is UGC-hard to obtain an approximation ratio lower than 3.