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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def initialize_time(self, control_freq):
 """ Initializes the time constants used for simulation. """

        self.cur_time = 0
        self.model_timestep = self.sim.model.opt.timestep
        if self.model_timestep <= 0:
            raise XMLError("xml model defined non-positive time step")
        self.control_freq = control_freq
        if control_freq <= 0:
            raise SimulationError(
                "control frequency {} is invalid".format(control_freq)
            )
        self.control_timestep = 1. / control_freq