newton.solvers.MuJoCoSolver

class newton.solvers.MuJoCoSolver(model, *, mjw_model=None, mjw_data=None, separate_envs_to_worlds=None, nefc_per_env=100, iterations=20, ls_iterations=10, solver='cg', integrator='euler', use_mujoco=False, disable_contacts=False, register_collision_groups=True, default_actuator_gear=None, actuator_gears=None, update_data_every=1, save_to_mjcf=None)

This solver provides an interface to simulate physics using the MuJoCo physics engine, optimized with GPU acceleration through mujoco_warp. It supports both MuJoCo and mujoco_warp backends, enabling efficient simulation of articulated systems with contacts and constraints.

Note

• This solver requires mujoco_warp and its dependencies to be installed.

• For installation instructions, see the mujoco_warp repository.

Example

solver = newton.MuJoCoSolver(model)

# simulation loop
for i in range(100):
    solver.step(model, state_in, state_out, control, contacts, dt)

Methods

__init__(model, *[, mjw_model, mjw_data, ...])
convert_to_mjc(model[, state, ...])	Convert a Newton model and state to MuJoCo (Warp) model and data.
integrate_bodies(model, state_in, state_out, dt)	Integrate the rigid bodies of the model.
integrate_particles(model, state_in, ...)	Integrate the particles of the model.
step(model, state_in, state_out, control, ...)	Simulate the model for a given time step using the given control input.

Attributes

device

Get the device used by the solver.

__init__(model, *, mjw_model=None, mjw_data=None, separate_envs_to_worlds=None, nefc_per_env=100, iterations=20, ls_iterations=10, solver='cg', integrator='euler', use_mujoco=False, disable_contacts=False, register_collision_groups=True, default_actuator_gear=None, actuator_gears=None, update_data_every=1, save_to_mjcf=None)

Parameters:

• model (Model) – the model to be simulated.

• mjw_model (MjWarpModel | None) – Optional pre-existing MuJoCo Warp model. If provided with mjw_data, conversion from Newton model is skipped.

• mjw_data (MjWarpData | None) – Optional pre-existing MuJoCo Warp data. If provided with mjw_model, conversion from Newton model is skipped.

• separate_envs_to_worlds (bool | None) – If True, each Newton environment is mapped to a separate MuJoCo world. Defaults to not use_mujoco.

• nefc_per_env (int) – Number of constraints per environment (world).

• iterations (int) – Number of solver iterations.

• ls_iterations (int) – Number of line search iterations for the solver.

• solver (int | str) – Solver type. Can be “cg” or “newton”, or their corresponding MuJoCo integer constants.

• integrator (int | str) – Integrator type. Can be “euler”, “rk4”, or “implicit”, or their corresponding MuJoCo integer constants.

• use_mujoco (bool) – If True, use the pure MuJoCo backend instead of mujoco_warp.

• disable_contacts (bool) – If True, disable contact computation in MuJoCo.

• register_collision_groups (bool) – If True, register collision groups from the Newton model in MuJoCo.

• default_actuator_gear (float | None) – Default gear ratio for all actuators. Can be overridden by actuator_gears.

• actuator_gears (dict[str, float] | None) – Dictionary mapping joint names to specific gear ratios, overriding the default_actuator_gear.

• update_data_every (int) – Frequency (in simulation steps) at which to update the MuJoCo Data object from the Newton state. If 0, Data is never updated after initialization.

• save_to_mjcf (str | None) – Optional path to save the generated MJCF model file.

step(model, state_in, state_out, control, contacts, dt)

Simulate the model for a given time step using the given control input.

Parameters:

• model (Model) – The model to simulate.

• state_in (State) – The input state.

• state_out (State) – The output state.

• dt (float) – The time step (typically in seconds).

• control (Control) – The control input. Defaults to None which means the control values from the Model are used.

notify_model_changed(flags)

Notify the solver that parts of the Model were modified.

The flags argument is a bit-mask composed of the NOTIFY_FLAG_* constants defined in newton.core.types. Each flag represents a category of model data that may have been updated after the solver was created. Passing the appropriate combination of flags enables a solver implementation to refresh its internal buffers without having to recreate the whole solver object. Valid flags are:

Constant	Description
NOTIFY_FLAG_JOINT_PROPERTIES	Joint transforms or coordinates have changed.
NOTIFY_FLAG_JOINT_AXIS_PROPERTIES	Joint axis limits, targets, or modes have changed.
NOTIFY_FLAG_DOF_PROPERTIES	Joint DOF state or force buffers have changed.
NOTIFY_FLAG_BODY_PROPERTIES	Rigid-body pose or velocity buffers have changed.
NOTIFY_FLAG_BODY_INERTIAL_PROPERTIES	Rigid-body mass or inertia tensors have changed.
NOTIFY_FLAG_SHAPE_PROPERTIES	Shape transforms or geometry have changed.

Parameters:

flags (int) – Bit-mask of model-update flags indicating which model properties changed.

property device: Device

Get the device used by the solver.

Returns:

The device used by the solver.

Return type:

wp.Device

integrate_bodies(model, state_in, state_out, dt, angular_damping=0.0)

Integrate the rigid bodies of the model.

Parameters:

• model (Model) – The model to integrate.

• state_in (State) – The input state.

• state_out (State) – The output state.

• dt (float) – The time step (typically in seconds).

• angular_damping (float, optional) – The angular damping factor. Defaults to 0.0.

integrate_particles(model, state_in, state_out, dt)

Integrate the particles of the model.

Parameters:

• model (Model) – The model to integrate.

• state_in (State) – The input state.

• state_out (State) – The output state.

• dt (float) – The time step (typically in seconds).

convert_to_mjc(model, state=None, *, separate_envs_to_worlds=True, iterations=20, ls_iterations=10, nefc_per_env=100, solver='cg', integrator='euler', disableflags=0, impratio=1.0, tolerance=1e-8, ls_tolerance=0.01, timestep=0.01, cone=0, register_collision_groups=True, joint_limit_threshold=1e3, geom_solref=(0.02, 1.0), geom_solimp=(0.9, 0.95, 0.001, 0.5, 2.0), geom_friction=(1.0, 0.05, 0.05), geom_condim=3, target_filename=None, default_actuator_args=None, default_actuator_gear=None, actuator_gears=None, actuated_axes=None, skip_visual_only_geoms=True, add_axes=True)

Convert a Newton model and state to MuJoCo (Warp) model and data.

Parameters:

• Model (newton.Model) – The Newton model to convert.

• State (newton.State) – The Newton state to convert.

Returns:

A tuple containing the model and data objects for mujoco_warp and MuJoCo.

Return type:

tuple[MjWarpModel, MjWarpData, MjModel, MjData]