Erdős and Simonovits asked the following question: For an integer r ≥ 2 and a family of non-bipartite graphs ℋ, what is the tight bound of α such that any ℋ-free n-vertex graph with minimum degree at least αn has chromatic number at most r? We answer this question for ℋ = {C_(2k+1)}, r ≥ 2 and k ≥ 3r + 4. This is a joint work with Yan Zilong and Yuan Xiaoli.

彭岳建，湖南大学数学学院教授、博士生导师。2001年于美国Emory大学获理学博士学位，2002-2012年在美国印第安纳州立大学数学系工作并获终身教授，后作为“湖南省百人计划”特聘教授回到湖南大学。彭岳建教授在极值组合、图论及相关领域做出了许多出色的工作，在国际组合图论权威刊物J. Combin. Theory Ser. B、J. Combin. Theory Ser. A、SIAM J. Discrete Math.、J. Graph Theory等发表论文90余篇。主持国家自然科学基金面上项目和重点项目。