Centipede#

../../../_images/centipede.gif

This environment is part of the Atari environments. Please read that page first for general information.

Action Space

Discrete(18)

Observation Shape

(210, 160, 3)

Observation High

255

Observation Low

0

Import

gymnasium.make("ALE/Centipede-v5")

For more Centipede variants with different observation and action spaces, see the variants section.

Description#

You are an elf and must use your magic wands to fend off spiders, fleas and centipedes. Your goal is to protect mushrooms in an enchanted forest. If you are bitten by a spider, flea or centipede, you will be temporally paralyzed and you will lose a magic wand. The game ends once you have lost all wands. You may receive additional wands after scoring a sufficient number of points.

For a more detailed documentation, see the AtariAge page

Actions#

Centipede has the action space Discrete(18) with the table below lists the meaning of each action’s meanings. As Centipede uses the full set of actions then specifying full_action_space=True will not modify the action space of the environment if passed to gymnasium.make.

Value

Meaning

Value

Meaning

Value

Meaning

0

NOOP

1

FIRE

2

UP

3

RIGHT

4

LEFT

5

DOWN

6

UPRIGHT

7

UPLEFT

8

DOWNRIGHT

9

DOWNLEFT

10

UPFIRE

11

RIGHTFIRE

12

LEFTFIRE

13

DOWNFIRE

14

UPRIGHTFIRE

15

UPLEFTFIRE

16

DOWNRIGHTFIRE

17

DOWNLEFTFIRE

Observations#

Atari environment have two possible observation types, the observation space is listed below. See variants section for the type of observation used by each environment id.

  • obs_type="rgb" -> observation_space=Box(0, 255, (210, 160, 3), np.uint8)

  • obs_type="ram" -> observation_space=Box(0, 255, (128,), np.uint8)

Additionally, obs_type="grayscale" cause the environment return a grayscale version of the rgb array for observations with the observation space being Box(0, 255, (210, 160), np.uint8)

Rewards#

You score points by hitting centipedes, scorpions, fleas and spiders. Additional points are awarded after every round (i.e. after you have lost a wand) for mushrooms that were not destroyed. Detailed documentation can be found on the AtariAge page.

Variants#

Centipede has the following variants of the environment id which have the following differences in observation, the number of frame-skips and the repeat action probability.

Env-id

obs_type=

frameskip=

repeat_action_probability=

Centipede-v0

"rgb"

(2, 5)

0.25

Centipede-ram-v0

"ram"

(2, 5)

0.25

Centipede-ramDeterministic-v0

"ram"

4

0.25

Centipede-ramNoFrameskip-v0

"ram"

1

0.25

CentipedeDeterministic-v0

"rgb"

4

0.25

CentipedeNoFrameskip-v0

"rgb"

1

0.25

Centipede-v4

"rgb"

(2, 5)

0.0

Centipede-ram-v4

"ram"

(2, 5)

0.0

Centipede-ramDeterministic-v4

"ram"

4

0.0

Centipede-ramNoFrameskip-v4

"ram"

1

0.0

CentipedeDeterministic-v4

"rgb"

4

0.0

CentipedeNoFrameskip-v4

"rgb"

1

0.0

ALE/Centipede-v5

"rgb"

4

0.25

ALE/Centipede-ram-v5

"ram"

4

0.25

Difficulty and modes#

It is possible to specify various flavors of the environment via the keyword arguments difficulty and mode. A flavor is a combination of a game mode and a difficulty setting. The table below lists the possible difficulty and mode values along with the default values.

Available Modes

Default Mode

Available Difficulties

Default Difficulty

[22, 86]

22

[0]

0

Version History#

A thorough discussion of the intricate differences between the versions and configurations can be found in the general article on Atari environments.

  • v5: Stickiness was added back and stochastic frameskipping was removed. The environments are now in the “ALE” namespace.

  • v4: Stickiness of actions was removed

  • v0: Initial versions release