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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 SwingUpEnv(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 -Inf Inf
+ 3 Pole Velocity At Tip -Inf Inf
+
+ Actions:
+ Type: Box(1)
+ Num Action Min Max
+ 0 Push cart -1 1
+
+ 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 reward 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.x_threshold = 2.4
+ self.x_dot_threshold = 10.
+ self.theta_dot_threshold = 3*np.pi
+
+ # Angle limit set to 2 * theta_threshold_radians so failing observation is still within bounds
+ high = np.array([
+ self.x_threshold*2,
+ self.x_dot_threshold,
+ np.finfo(np.float32).max,
+ np.finfo(np.float32).max])
+
+
+ self.action_space = spaces.Box(-np.ones(1),np.ones(1),dtype=np.float32)
+ 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):
+ assert self.action_space.contains(action), "%r (%s) invalid"%(action, type(action))
+ state = self.state
+ x, x_dot, theta, theta_dot = state
+ force = self.force_mag * action[0]
+
+ costheta = math.cos(theta)
+ sintheta = math.sin(theta)
+
+ if costheta > 0:
+ self.up_time += 1
+ self.max_up_time = np.max([self.up_time,self.max_up_time])
+
+ else:
+ self.up_time = 0
+
+ temp = (force + self.polemass_length * theta_dot * theta_dot * sintheta) / self.total_mass
+ thetaacc = (self.gravity * sintheta - costheta* temp) / (self.length * (4.0/3.0 - self.masspole * costheta * costheta / 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 = x < -self.x_threshold \
+ or x > self.x_threshold \
+ or theta_dot < -self.theta_dot_threshold \
+ or theta_dot > self.theta_dot_threshold
+ done = bool(done)
+
+ if not done:
+ reward = np.ceil(costheta)
+ elif self.steps_beyond_done is None:
+ # Pole just fell!
+ self.steps_beyond_done = 0
+ reward = -(100 * (np.abs(x_dot)+np.abs(theta_dot)))
+ 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, {'max_up_time' : self.max_up_time}
+
+ def reset(self):
+ self.state = self.np_random.uniform(low=-.5,high=.5,size=(4,))
+ self.state[2] += np.pi
+ self.up_time = 0
+ self.max_up_time = 0
+ self.up = False
+ 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[0]*scale+screen_width/2.0 # MIDDLE OF CART
+ self.carttrans.set_translation(cartx, carty)
+ self.poletrans.set_rotation(-x[2])
+
+ return self.viewer.render(return_rgb_array = mode=='rgb_array')
+
+ def close(self):
+ if self.viewer:
+ self.viewer.close()
+ self.viewer = None