trep
- param system
An instance of
Systemto add the constraint to.- type system
System- param name
A string that uniquely identifies the constraint.
- param tolerance
Tolerance to consider the constraint satisfied.
- type tolerance
Float
This is the base class for all holonomic constraints in a System. It should never be created directly. Constraints are created by instantiating a specific type of constraint.
See builtin_constraints for the built-in types of constraints. Additional constraints can be added through either the Python or C-API.
Holonomic constraints restrict the allowable configurations of a mechanical system. Every constraint has an associated constraint function h(q) : Q → R. A configuration q is acceptable if and only if h(q) = 0.
Constraint.system
The System that this constraint belongs to.
(read-only)
Constraint.name
The name of this constraint or None.
Constraint.index
The index of the constraint in System.constraints. This is also the index of the constraint's force in any values of λ or its derivatives used through trep.
(read-only)
Constraint.tolerance
The constraint should be considered satisfied if |h(q)| < tolerance. This is primarly used by the variational integrator when it finds the next configuration, or by System.satisfy_constraints().
Constraint.h()
- rtype
Float
Return the value of the constraint function at the system's current state. This function should be implemented by derived Constraints.
Constraint.h_dq(q1)
- param q1
Derivative variable
- type q1
Config- rtype
Float
Return the derivative of h with respect to q1.
Constraint.h_dqdq(q1, q2)
- param q1
Derivative variable
- type q1
Config- param q2
Derivative variable
- type q2
Config- rtype
Float
Return the second derivative of h with respect to q1 and q2.
Constraint.h_dqdqdq(q1, q2, q3)
- param q1
Derivative variable
- type q1
Config- param q2
Derivative variable
- type q2
Config- param q3
Derivative variable
- type q3
Config- rtype
Float
Return the third derivative of h with respect to q1, q2, and q3.
Constraint.h_dqdqdqdq(q1, q2, q3, q4)
- param q1
Derivative variable
- type q1
Config- param q2
Derivative variable
- type q2
Config- param q3
Derivative variable
- type q3
Config- param q4
Derivative variable
- type q4
Config- rtype
Float
Return the fourth derivative of h with respect to q1, q2, q3, and q4.
It is important that the derivatives of h are correct. The easiest way to check their correctness is to approximate each derivative using numeric differentiation. These methods are provided to perform this test. The derivatives are only compared at the current configuration of the system. For improved coverage, try running each test several times at different configurations.
Constraint.validate_h_dq(delta=1e-6, tolerance=1e-6, verbose=False) Constraint.validate_h_dqdq(delta=1e-6, tolerance=1e-6, verbose=False) Constraint.validate_h_dqdqdq(delta=1e-6, tolerance=1e-6, verbose=False) Constraint.validate_h_dqdqdqdq(delta=1e-6, tolerance=1e-6, verbose=False)
- param delta
Amount to add to each configuration
- param tolerance
Acceptable difference between the calculated and approximate derivatives
- param verbose
Boolean to print error and result messages.
- rtype
Boolean indicating if all tests passed
Check the derivatives against the approximate numeric derivative calculated from one less derivative (ie, approximate h_dq from h and h_dqdq from h_dq).
See System.test_derivative_dq for details of the approximation and comparison.
Constraint.opengl_draw()
Draw a representation of this constraint in the current OpenGL context. The OpenGL coordinate frame will be in the System's root coordinate frame.
This function is called by the automatic visualization tools. The default implementation does nothing.