    def optimize_Tc(self):
        '''
        determines the coalescent time scale that optimizes the coalescent likelihood of the tree
        '''
        from scipy.optimize import minimize_scalar
        initial_Tc = self.Tc
        def cost(Tc):
            self.set_Tc(Tc)
            return -self.total_LH()

        sol = minimize_scalar(cost, bounds=[ttconf.TINY_NUMBER,10.0])
        if "success" in sol and sol["success"]:
            self.set_Tc(sol['x'])
        else:
            self.logger("merger_models:optimze_Tc: optimization of coalescent time scale failed: " + str(sol), 0, warn=True)
            self.set_Tc(initial_Tc.y, T=initial_Tc.x)