What does the ending of Pi mean to you?

Well the ending is quite simple if we do not try to give unnecessary wings to our imagination. It is a story about a genius who has to carry his burden of being a genius and perform his self imposed duties of doing something miraculous to benefit the mankind. He is ambitious and devoted but the genius is taking its toll on him. He has to fight his growing hallucinations and battle between reality and illusion. So at the end he is tired of all this and damages that part of the brain which is responsible for his higher mathematical skills. At the end when the girl comes up to him, that scene is used to depict that he has lost his mathematical skills and is now at peace with himself, for he is found smiling.