---
title: Centipede
---

# Centipede

```{figure} ../../_static/videos/atari/centipede.gif
:width: 120px
:name: Centipede
```

This environment is part of the <a href='..'>Atari environments</a>. Please read that page first for general information.

## 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](https://atariage.com/manual_html_page.php?SoftwareID=911)

## 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         |
|---------|-----------------|
| `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](https://atariage.com/manual_html_page.php?SoftwareID=911).

## 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
