def METHOD_NAME(self, x, first_step=False):
    if first_step:
        self.log = Log([['O'], ['E_f', 'E_m'], ['v_f', 'v_m']],
            ylabels=['Obj. fun.', "Young's modulus", "Poisson's ratio"],
            xlabels=['iter', 'iter', 'iter'],
            aggregate=0)
        self.istep = 0
        self.log(0.5, x[0], x[2], x[1], x[3],
            x=[0, 0, 0, 0])
    else:
        self.istep += 1
        self.log(self.eval_f[-1], x[0], x[2], x[1], x[3],
            x=(self.istep,)*4)