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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 start_circle_left(self, radius_m, velocity=VELOCITY):
 """ Start a circular motion to the left. This function returns immediately. :param radius_m: The radius of the circle (meters) :param velocity: The velocity of the motion (meters/second) :return: """

        circumference = 2 * radius_m * math.pi
        rate = 360.0 * velocity / circumference

        self._set_vel_setpoint(velocity, 0.0, 0.0, -rate)