newton.solvers.SolverBase#

class newton.solvers.SolverBase(model)[source]#

Bases: object

Generic base class for solvers.

The implementation provides helper kernels to integrate rigid bodies and particles. Concrete solver back-ends should derive from this class and override step() as well as notify_model_changed() where necessary.

classmethod register_custom_attributes(builder)#

Register custom attributes for the solver.

Parameters:

builder (ModelBuilder) – The model builder to register the custom attributes to.

__init__(model)#
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).

notify_model_changed(flags)#

Notify the solver that parts of the Model were modified.

The flags argument is a bit-mask composed of the ModelFlags enums or custom int bits. 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:

  • ModelFlags.JOINT_PROPERTIES: Joint transforms or coordinates have changed.

  • ModelFlags.JOINT_DOF_PROPERTIES: Joint axis limits, targets, modes, DOF state, or force buffers have changed.

  • ModelFlags.BODY_PROPERTIES: Rigid-body pose or velocity buffers have changed.

  • ModelFlags.BODY_INERTIAL_PROPERTIES: Rigid-body mass or inertia tensors have changed.

  • ModelFlags.SHAPE_PROPERTIES: Shape transforms or geometry have changed.

  • ModelFlags.MODEL_PROPERTIES: Model global properties (e.g., gravity) have changed.

  • ModelFlags.CONSTRAINT_PROPERTIES: Constraint definitions, coefficients, or enable flags have changed.

  • ModelFlags.TENDON_PROPERTIES: Tendon stiffness or related tendon properties have changed.

  • ModelFlags.ACTUATOR_PROPERTIES: Actuator gains, biases, limits, or force properties have changed.

Parameters:

flags (ModelFlags | int) – Bit-mask of ModelFlags or custom int bits indicating which model properties changed.

reset(state, world_mask=None, flags=None)#

Reset the solver internal state data.

Modifies the given state in place. Derived solvers override this to reset solver-specific internal buffers or custom state attributes when environments are reset (e.g. during RL training).

The default implementation is a no-op so solvers that do not require special reset logic need not override this method.

Parameters:

  • state (State) – The simulation state to reset (modified in place).

  • world_mask (array | None) – Optional boolean mask of shape (num_worlds,) specifying which worlds to reset. If None, all worlds are reset.

  • flags (StateFlags | int | None) – Optional StateFlags or int bitmask controlling which state attributes need to be reset. If None, all state attributes are reset.

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

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

Parameters:

  • state_in (State) – The input state.

  • state_out (State) – The output state.

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

  • contacts (Contacts | None) – The contact information.

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

update_contacts(contacts, state=None)#

Update a Contacts object with forces from the solver state. Where the solver state contains other contact data, convert that data to the Contacts format.

Parameters:

  • contacts (Contacts) – The object to update from the solver state.

  • state (State | None) – Optional simulation state, used by some solvers.

property device: Device#

Get the device used by the solver.

Returns:

The device used by the solver.

Return type:

wp.Device