class CartPole(Environment):
"""
The Inverted Pendulum on a Cart environment as presented in:
"Least-Squares Policy Iteration". Lagoudakis M. G. and Parr R.. 2003.
"""
def __init__(self,
m=2.,
M=8.,
l=.5,
g=9.8,
mu=1e-2,
max_u=50.,
noise_u=10.,
horizon=3000,
gamma=.95):
"""
Constructor.
Args:
m (float, 2.0): mass of the pendulum;
M (float, 8.0): mass of the cart;
l (float, .5): length of the pendulum;
g (float, 9.8): gravity acceleration constant;
max_u (float, 50.): maximum allowed input torque;
noise_u (float, 10.): maximum noise on the action;
horizon (int, 3000): horizon of the problem;
gamma (float, .95): discount factor.
"""
# MDP parameters
self._m = m
self._M = M
self._l = l
self._g = g
self._alpha = 1 / (self._m + self._M)
self._mu = mu
self._dt = .1
self._max_u = max_u
self._noise_u = noise_u
high = np.array([np.inf, np.inf])
# MDP properties
observation_space = spaces.Box(low=-high, high=high)
action_space = spaces.Discrete(3)
mdp_info = MDPInfo(observation_space, action_space, gamma, horizon)
# Visualization
self._viewer = Viewer(2.5 * l, 2.5 * l)
self._last_u = None
self._state = None
super().__init__(mdp_info)
def reset(self, state=None):
if state is None:
angle = np.random.uniform(-np.pi / 8., np.pi / 8.)
self._state = np.array([angle, 0.])
else:
self._state = state
self._state[0] = normalize_angle(self._state[0])
self._last_u = 0
return self._state
def step(self, action):
if action == 0:
u = -self._max_u
elif action == 1:
u = 0.
else:
u = self._max_u
self._last_u = u
u += np.random.uniform(-self._noise_u, self._noise_u)
new_state = odeint(self._dynamics, self._state, [0, self._dt], (u, ))
self._state = np.array(new_state[-1])
self._state[0] = normalize_angle(self._state[0])
if np.abs(self._state[0]) > np.pi * .5:
reward = -1.
absorbing = True
else:
reward = 0.
absorbing = False
return self._state, reward, absorbing, {}
def render(self, mode='human'):
start = 1.25 * self._l * np.ones(2)
end = 1.25 * self._l * np.ones(2)
end[0] += self._l * np.sin(self._state[0])
end[1] += self._l * np.cos(self._state[0])
self._viewer.line(start, end)
self._viewer.square(start, 0, self._l / 10)
self._viewer.circle(end, self._l / 20)
direction = -np.sign(self._last_u) * np.array([1, 0])
value = np.abs(self._last_u)
self._viewer.force_arrow(start, direction, value, self._max_u,
self._l / 5)
self._viewer.display(self._dt)
def stop(self):
self._viewer.close()
def _dynamics(self, state, t, u):
theta = state[0]
omega = state[1]
d_theta = omega
d_omega = (self._g * np.sin(theta) - self._alpha * self._m * self._l *
.5 * d_theta**2 * np.sin(2 * theta) * .5 -
self._alpha * np.cos(theta) * u) / (
2 / 3 * self._l -
self._alpha * self._m * self._l * .5 * np.cos(theta)**2)
return d_theta, d_omega
class AbstractGridWorld(Environment):
"""
Abstract class to build a grid world.
"""
def __init__(self, mdp_info, height, width, start, goal):
"""
Constructor.
Args:
height (int): height of the grid;
width (int): width of the grid;
start (tuple): x-y coordinates of the goal;
goal (tuple): x-y coordinates of the goal.
"""
assert not np.array_equal(start, goal)
assert goal[0] < height and goal[1] < width,\
'Goal position not suitable for the grid world dimension.'
self._state = None
self._height = height
self._width = width
self._start = start
self._goal = goal
# Visualization
self._viewer = Viewer(self._width, self._height, 500,
self._height * 500 // self._width)
super().__init__(mdp_info)
def reset(self, state=None):
if state is None:
state = self.convert_to_int(self._start, self._width)
self._state = state
return self._state
def step(self, action):
state = self.convert_to_grid(self._state, self._width)
new_state, reward, absorbing, info = self._step(state, action)
self._state = self.convert_to_int(new_state, self._width)
return self._state, reward, absorbing, info
def render(self):
for row in range(1, self._height):
for col in range(1, self._width):
self._viewer.line(np.array([col, 0]),
np.array([col, self._height]))
self._viewer.line(np.array([0, row]),
np.array([self._width, row]))
goal_center = np.array(
[.5 + self._goal[1], self._height - (.5 + self._goal[0])])
self._viewer.square(goal_center, 0, 1, (0, 255, 0))
start_grid = self.convert_to_grid(self._start, self._width)
start_center = np.array(
[.5 + start_grid[1], self._height - (.5 + start_grid[0])])
self._viewer.square(start_center, 0, 1, (255, 0, 0))
state_grid = self.convert_to_grid(self._state, self._width)
state_center = np.array(
[.5 + state_grid[1], self._height - (.5 + state_grid[0])])
self._viewer.circle(state_center, .4, (0, 0, 255))
self._viewer.display(.1)
def _step(self, state, action):
raise NotImplementedError('AbstractGridWorld is an abstract class.')
def _grid_step(self, state, action):
if action == 0:
if state[0] > 0:
state[0] -= 1
elif action == 1:
if state[0] + 1 < self._height:
state[0] += 1
elif action == 2:
if state[1] > 0:
state[1] -= 1
elif action == 3:
if state[1] + 1 < self._width:
state[1] += 1
@staticmethod
def convert_to_grid(state, width):
return np.array([state[0] // width, state[0] % width])
@staticmethod
def convert_to_int(state, width):
return np.array([state[0] * width + state[1]])
