Terminations

Termination terms define when an episode ends. Each term is a function that returns a boolean per-environment tensor every step. The termination manager aggregates all terms and reports the result to the training framework as either a terminal failure or a truncation.

Each term is registered by name with a TerminationTermCfg. Setting time_out=True marks the condition as a truncation rather than a terminal failure. Truncations map to the truncated signal in the Gym interface; failures map to terminated. This distinction matters for value bootstrapping: the agent should estimate future value beyond a truncation but not beyond a failure.

from mjlab.envs.mdp import terminations
from mjlab.managers.termination_manager import TerminationTermCfg

terminations_cfg = {
    "time_out": TerminationTermCfg(
        func=terminations.time_out, time_out=True,
    ),
    "fallen": TerminationTermCfg(
        func=terminations.bad_orientation,
        params={"limit_angle": 1.0},
    ),
}

Built-in termination functions

The functions below are available in mjlab.envs.mdp.terminations and are shared across tasks. Individual tasks may define additional termination functions specific to their objective. All termination functions return a boolean tensor of shape [num_envs].

Function	Description
time_out	Returns True when the episode length reaches env.max_episode_length. Register with time_out=True so the manager treats it as a truncation.
bad_orientation	Returns True when the angle between the asset’s up axis and world up exceeds limit_angle (radians).
root_height_below_minimum	Returns True when the asset’s root link height is below minimum_height (meters).
nan_detection	Returns True when NaN or Inf values appear anywhere in the physics state. A safety net to terminate diverged simulations cleanly.

Writing custom termination functions

Custom termination functions follow the same patterns as reward functions. A plain function accepts env and returns a boolean [num_envs] tensor. See Term configuration pattern for the general pattern.