Struct ConvexAdjointGradients 

pub struct ConvexAdjointGradients {
    pub objective: f64,
    pub d_q0: DVec,
    pub d_v0: DVec,
    pub d_ctrl: Vec<DVec>,
    pub d_inertia: Vec<[f64; 10]>,
    pub d_friction: f64,
    pub d_restitution: f64,
}

Everything one unified backward pass produces.

Fields

objective: f64

The objective at the nominal rollout.

d_q0: DVec

dJ/dq0 (length nq).

d_v0: DVec

dJ/dv0 (length nv).

d_ctrl: Vec<DVec>

dJ/du_t per step (each length nv).

d_inertia: Vec<[f64; 10]>

dJ/dπ per body, canonical packing [m, cx, cy, cz, Ixx, Iyy, Izz, Ixy, Ixz, Iyz].

d_friction: f64

dJ/dμ — the friction coefficient of ConvexContactRollout::material.

One scalar, not one per contact, because the rollout applies a single material to every body; this is the total derivative with respect to that shared coefficient.

Only sliding contacts contribute. A sticking contact sits strictly inside the cone, so moving the cone boundary does not move the solution, and a separating one carries no impulse. So a trajectory that never slips reports exactly 0 here — a real property of Coulomb friction rather than a missing term, and one a finite difference reproduces exactly.

d_restitution: f64

dJ/de — the restitution coefficient of ConvexContactRollout::material, likewise a single shared scalar.

Zero for any trajectory whose contacts all approach below ContactSolverConfig::restitution_threshold, where the low-speed ramp has taken the effective restitution to zero — again a genuine flat region of the model, not an omission.