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```* documentation matches code

The returned angle is returned in the unit of radians and not degrees.

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 """ Classic cart-pole system implemented by Rich Sutton et al. Copied from http://incompleteideas.net/sutton/book/code/pole.c permalink: https://perma.cc/C9ZM-652R """ import math import gym from gym import spaces, logger from gym.utils import seeding import numpy as np class CartPoleEnv(gym.Env): """ Description: A pole is attached by an un-actuated joint to a cart, which moves along a frictionless track. The pendulum starts upright, and the goal is to prevent it from falling over by increasing and reducing the cart's velocity. Source: This environment corresponds to the version of the cart-pole problem described by Barto, Sutton, and Anderson Observation: Type: Box(4) Num Observation Min Max 0 Cart Position -4.8 4.8 1 Cart Velocity -Inf Inf 2 Pole Angle -0.418 rad (-24 deg) 0.418 rad (24 deg) 3 Pole Angular Velocity -Inf Inf Actions: Type: Discrete(2) Num Action 0 Push cart to the left 1 Push cart to the right Note: The amount the velocity that is reduced or increased is not fixed; it depends on the angle the pole is pointing. This is because the center of gravity of the pole increases the amount of energy needed to move the cart underneath it Reward: Reward is 1 for every step taken, including the termination step Starting State: All observations are assigned a uniform random value in [-0.05..0.05] Episode Termination: Pole Angle is more than 12 degrees. Cart Position is more than 2.4 (center of the cart reaches the edge of the display). Episode length is greater than 200. Solved Requirements: Considered solved when the average return is greater than or equal to 195.0 over 100 consecutive trials. """ metadata = { 'render.modes': ['human', 'rgb_array'], 'video.frames_per_second': 50 } def __init__(self): self.gravity = 9.8 self.masscart = 1.0 self.masspole = 0.1 self.total_mass = (self.masspole + self.masscart) self.length = 0.5 # actually half the pole's length self.polemass_length = (self.masspole * self.length) self.force_mag = 10.0 self.tau = 0.02 # seconds between state updates self.kinematics_integrator = 'euler' # Angle at which to fail the episode self.theta_threshold_radians = 12 * 2 * math.pi / 360 self.x_threshold = 2.4 # Angle limit set to 2 * theta_threshold_radians so failing observation # is still within bounds. high = np.array([self.x_threshold * 2, np.finfo(np.float32).max, self.theta_threshold_radians * 2, np.finfo(np.float32).max], dtype=np.float32) self.action_space = spaces.Discrete(2) self.observation_space = spaces.Box(-high, high, dtype=np.float32) self.seed() self.viewer = None self.state = None self.steps_beyond_done = None def seed(self, seed=None): self.np_random, seed = seeding.np_random(seed) return [seed] def step(self, action): err_msg = "%r (%s) invalid" % (action, type(action)) assert self.action_space.contains(action), err_msg x, x_dot, theta, theta_dot = self.state force = self.force_mag if action == 1 else -self.force_mag costheta = math.cos(theta) sintheta = math.sin(theta) # For the interested reader: # https://coneural.org/florian/papers/05_cart_pole.pdf temp = (force + self.polemass_length * theta_dot ** 2 * sintheta) / self.total_mass thetaacc = (self.gravity * sintheta - costheta * temp) / (self.length * (4.0 / 3.0 - self.masspole * costheta ** 2 / self.total_mass)) xacc = temp - self.polemass_length * thetaacc * costheta / self.total_mass if self.kinematics_integrator == 'euler': x = x + self.tau * x_dot x_dot = x_dot + self.tau * xacc theta = theta + self.tau * theta_dot theta_dot = theta_dot + self.tau * thetaacc else: # semi-implicit euler x_dot = x_dot + self.tau * xacc x = x + self.tau * x_dot theta_dot = theta_dot + self.tau * thetaacc theta = theta + self.tau * theta_dot self.state = (x, x_dot, theta, theta_dot) done = bool( x < -self.x_threshold or x > self.x_threshold or theta < -self.theta_threshold_radians or theta > self.theta_threshold_radians ) if not done: reward = 1.0 elif self.steps_beyond_done is None: # Pole just fell! self.steps_beyond_done = 0 reward = 1.0 else: if self.steps_beyond_done == 0: logger.warn( "You are calling 'step()' even though this " "environment has already returned done = True. You " "should always call 'reset()' once you receive 'done = " "True' -- any further steps are undefined behavior." ) self.steps_beyond_done += 1 reward = 0.0 return np.array(self.state), reward, done, {} def reset(self): self.state = self.np_random.uniform(low=-0.05, high=0.05, size=(4,)) self.steps_beyond_done = None return np.array(self.state) def render(self, mode='human'): screen_width = 600 screen_height = 400 world_width = self.x_threshold * 2 scale = screen_width/world_width carty = 100 # TOP OF CART polewidth = 10.0 polelen = scale * (2 * self.length) cartwidth = 50.0 cartheight = 30.0 if self.viewer is None: from gym.envs.classic_control import rendering self.viewer = rendering.Viewer(screen_width, screen_height) l, r, t, b = -cartwidth / 2, cartwidth / 2, cartheight / 2, -cartheight / 2 axleoffset = cartheight / 4.0 cart = rendering.FilledPolygon([(l, b), (l, t), (r, t), (r, b)]) self.carttrans = rendering.Transform() cart.add_attr(self.carttrans) self.viewer.add_geom(cart) l, r, t, b = -polewidth / 2, polewidth / 2, polelen - polewidth / 2, -polewidth / 2 pole = rendering.FilledPolygon([(l, b), (l, t), (r, t), (r, b)]) pole.set_color(.8, .6, .4) self.poletrans = rendering.Transform(translation=(0, axleoffset)) pole.add_attr(self.poletrans) pole.add_attr(self.carttrans) self.viewer.add_geom(pole) self.axle = rendering.make_circle(polewidth/2) self.axle.add_attr(self.poletrans) self.axle.add_attr(self.carttrans) self.axle.set_color(.5, .5, .8) self.viewer.add_geom(self.axle) self.track = rendering.Line((0, carty), (screen_width, carty)) self.track.set_color(0, 0, 0) self.viewer.add_geom(self.track) self._pole_geom = pole if self.state is None: return None # Edit the pole polygon vertex pole = self._pole_geom l, r, t, b = -polewidth / 2, polewidth / 2, polelen - polewidth / 2, -polewidth / 2 pole.v = [(l, b), (l, t), (r, t), (r, b)] x = self.state cartx = x * scale + screen_width / 2.0 # MIDDLE OF CART self.carttrans.set_translation(cartx, carty) self.poletrans.set_rotation(-x) return self.viewer.render(return_rgb_array=mode == 'rgb_array') def close(self): if self.viewer: self.viewer.close() self.viewer = None