在学习强化学习，为什么强化学习的gym.reset() 返回的是一个不为零的数组，我理解的重置不就是归零吗？ 比如
CartPole-v0 环境。为什么def reset()那儿要返回4个-0.05到0.05的随机数呢？
def reset(
self,
*,
seed: Optional[int] = None,
return_info: bool = False,
options: Optional[dict] = None,
):
super().reset(seed=seed)
** self.state = self.np_random.uniform(low=-0.05, high=0.05, size=(4,))
** self.steps_beyond_done = None
if not return_info:
return np.array(self.state, dtype=np.float32)
else:
return np.array(self.state, dtype=np.float32), {}
"""
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
from typing import Optional, Union
import numpy as np
import gym
from gym import logger, spaces
from gym.error import DependencyNotInstalled
class CartPoleEnv(gym.Env[np.ndarray, Union[int, np.ndarray]]):
"""
### Description
This environment corresponds to the version of the cart-pole problem described by Barto, Sutton, and Anderson in
["Neuronlike Adaptive Elements That Can Solve Difficult Learning Control Problem"](https://ieeexplore.ieee.org/document/6313077).
A pole is attached by an un-actuated joint to a cart, which moves along a frictionless track.
The pendulum is placed upright on the cart and the goal is to balance the pole by applying forces
in the left and right direction on the cart.
### Action Space
The action is a `ndarray` with shape `(1,)` which can take values `{0, 1}` indicating the direction
of the fixed force the cart is pushed with.
| Num | Action |
|-----|------------------------|
| 0 | Push cart to the left |
| 1 | Push cart to the right |
**Note**: The velocity that is reduced or increased by the applied force is not fixed and it depends on the angle
the pole is pointing. The center of gravity of the pole varies the amount of energy needed to move the cart underneath it
### Observation Space
The observation is a `ndarray` with shape `(4,)` with the values corresponding to the following positions and velocities:
| Num | Observation | Min | Max |
|-----|-----------------------|---------------------|-------------------|
| 0 | Cart Position | -4.8 | 4.8 |
| 1 | Cart Velocity | -Inf | Inf |
| 2 | Pole Angle | ~ -0.418 rad (-24°) | ~ 0.418 rad (24°) |
| 3 | Pole Angular Velocity | -Inf | Inf |
**Note:** While the ranges above denote the possible values for observation space of each element,
it is not reflective of the allowed values of the state space in an unterminated episode. Particularly:
- The cart x-position (index 0) can be take values between `(-4.8, 4.8)`, but the episode terminates
if the cart leaves the `(-2.4, 2.4)` range.
- The pole angle can be observed between `(-.418, .418)` radians (or **±24°**), but the episode terminates
if the pole angle is not in the range `(-.2095, .2095)` (or **±12°**)
### Rewards
Since the goal is to keep the pole upright for as long as possible, a reward of `+1` for every step taken,
including the termination step, is allotted. The threshold for rewards is 475 for v1.
### Starting State
All observations are assigned a uniformly random value in `(-0.05, 0.05)`
### Episode Termination
The episode terminates if any one of the following occurs:
1. Pole Angle is greater than ±12°
2. Cart Position is greater than ±2.4 (center of the cart reaches the edge of the display)
3. Episode length is greater than 500 (200 for v0)
### Arguments
```
gym.make('CartPole-v1')
```
No additional arguments are currently supported.
"""
metadata = {"render_modes": ["human", "rgb_array"], "render_fps": 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.screen = None
self.clock = None
self.isopen = True
self.state = None
self.steps_beyond_done = None
def step(self, action):
err_msg = f"{action!r} ({type(action)}) invalid"
assert self.action_space.contains(action), err_msg
assert self.state is not None, "Call reset before using step method."
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, dtype=np.float32), reward, done, {}
def reset(
self,
*,
seed: Optional[int] = None,
return_info: bool = False,
options: Optional[dict] = None,
):
super().reset(seed=seed)
self.state = self.np_random.uniform(low=-0.05, high=0.05, size=(4,))
self.steps_beyond_done = None
if not return_info:
return np.array(self.state, dtype=np.float32)
else:
return np.array(self.state, dtype=np.float32), {}
def render(self, mode="human"):
try:
import pygame
from pygame import gfxdraw
except ImportError:
raise DependencyNotInstalled(
"pygame is not installed, run `pip install gym[classic_control]`"
)
screen_width = 600
screen_height = 400
world_width = self.x_threshold * 2
scale = screen_width / world_width
polewidth = 10.0
polelen = scale * (2 * self.length)
cartwidth = 50.0
cartheight = 30.0
if self.state is None:
return None
x = self.state
if self.screen is None:
pygame.init()
pygame.display.init()
self.screen = pygame.display.set_mode((screen_width, screen_height))
if self.clock is None:
self.clock = pygame.time.Clock()
self.surf = pygame.Surface((screen_width, screen_height))
self.surf.fill((255, 255, 255))
l, r, t, b = -cartwidth / 2, cartwidth / 2, cartheight / 2, -cartheight / 2
axleoffset = cartheight / 4.0
cartx = x[0] * scale + screen_width / 2.0 # MIDDLE OF CART
carty = 100 # TOP OF CART
cart_coords = [(l, b), (l, t), (r, t), (r, b)]
cart_coords = [(c[0] + cartx, c[1] + carty) for c in cart_coords]
gfxdraw.aapolygon(self.surf, cart_coords, (0, 0, 0))
gfxdraw.filled_polygon(self.surf, cart_coords, (0, 0, 0))
l, r, t, b = (
-polewidth / 2,
polewidth / 2,
polelen - polewidth / 2,
-polewidth / 2,
)
pole_coords = []
for coord in [(l, b), (l, t), (r, t), (r, b)]:
coord = pygame.math.Vector2(coord).rotate_rad(-x[2])
coord = (coord[0] + cartx, coord[1] + carty + axleoffset)
pole_coords.append(coord)
gfxdraw.aapolygon(self.surf, pole_coords, (202, 152, 101))
gfxdraw.filled_polygon(self.surf, pole_coords, (202, 152, 101))
gfxdraw.aacircle(
self.surf,
int(cartx),
int(carty + axleoffset),
int(polewidth / 2),
(129, 132, 203),
)
gfxdraw.filled_circle(
self.surf,
int(cartx),
int(carty + axleoffset),
int(polewidth / 2),
(129, 132, 203),
)
gfxdraw.hline(self.surf, 0, screen_width, carty, (0, 0, 0))
self.surf = pygame.transform.flip(self.surf, False, True)
self.screen.blit(self.surf, (0, 0))
if mode == "human":
pygame.event.pump()
self.clock.tick(self.metadata["render_fps"])
pygame.display.flip()
if mode == "rgb_array":
return np.transpose(
np.array(pygame.surfarray.pixels3d(self.screen)), axes=(1, 0, 2)
)
else:
return self.isopen
def close(self):
if self.screen is not None:
import pygame
pygame.display.quit()
pygame.quit()
self.isopen = False
