Struct SolRef 

pub struct SolRef {
    pub timeconst: f64,
    pub dampratio: f64,
}

MuJoCo-style solref: the reference response of a violated constraint.

The pair (timeconst, dampratio) describes the mass-normalized damped spring the solver pretends the constraint is, rather than a raw stiffness/damping pair. Parameterizing by a time constant is what makes the behaviour independent of the contacting bodies’ masses: a 20 ms recovery is 20 ms whether the box weighs a gram or a tonne.

Fields

timeconst: f64

Time constant of the constraint’s reference response, in seconds.

MuJoCo’s default is 0.02, and its guidance — that it should be at least twice the timestep — applies here for the same reason: the discrete correction below reduces to a per-step gain of dt / (2*timeconst*dampratio^2 + dt), which saturates at 1 (a full, popping correction in one step) as timeconst -> 0.

dampratio: f64

Damping ratio. 1 is critically damped, which is what a contact wants: penetration decays without overshooting into a bounce.

Implementations

impl SolRef

pub fn error_reduction(&self, dt: f64) -> f64

Fraction of the current penetration to remove in a step of dt.

Derived from the reference spring rather than picked: a critically damped spring with time constant tau and damping ratio zeta has mass-normalized k = 1/(tau^2 zeta^2) and b = 2/(tau zeta^2). One implicit step of that spring removes

  dt*k / (b + dt*k)  =  dt / (2*tau*zeta^2 + dt)

of the violation. Taking the implicit (rather than the explicit dt^2 k) gain is what keeps the correction bounded by 1 for every dt, so a large step can never over-correct and launch the body.

Trait Implementations

impl Clone for SolRef

fn clone(&self) -> SolRef

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for SolRef

impl Debug for SolRef

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for SolRef

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for SolRef

fn eq(&self, other: &SolRef) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for SolRef