<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def restore_values(self):
 """ Restore x, y, and f values if not converged Returns ------- None """

        if self.convergence is True:
            return
        dae = self.system.dae
        system = self.system

        inc_g = self.inc[dae.n:dae.m + dae.n]
        max_g_err_sign = 1 if abs(max(inc_g)) > abs(min(inc_g)) else -1
        if max_g_err_sign == 1:
            max_g_err_idx = list(inc_g).index(max(inc_g))
        else:
            max_g_err_idx = list(inc_g).index(min(inc_g))
        logger.debug(
            'Maximum mismatch = {:.4g} at equation <{}>'.format(
                max(abs(inc_g)), system.varname.unamey[max_g_err_idx]))
        logger.debug(
            'Reducing time step h={:.4g}s for t={:.4g}'.format(self.h, self.t))

        # restore initial variable data
        dae.x = matrix(self.x0)
        dae.y = matrix(self.y0)
        dae.f = matrix(self.f0)