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nav: DynBikePH.Golden, the pH form and its books for GRL-SNAM's twin - #848
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A golden for dyn_bike's port-Hamiltonian form, as DynBike.Golden is for the plant: tests/data/dyn_bike_ph_golden.json, written with CVC_DYN_BIKE_PH_GOLDEN_WRITE=1 and otherwise checked to 1e-9 relative. On DynBike.Golden's Humvee (lags, low-speed blend), at its seven states (cruising, a hard corner, trail braking, past the tire's peak, backing up, creeping, pulling away from rest) and a stop at the speed clamp, each case records: - the parts at its state (dyn_ph_parts_at): u, sg, Fxf, Fxr, Fyf, Fyr, wf, wr, w0f, the secants Sf and Sr, Dx, cos delta; - the rates at its state (dyn_ph_rates_at): dissipated, supplied, floor, grade; - one dyn_plant_books step: the next state, the twist before the limiters (dyn_step_free), and the books (dH, the trapezoid's dissipated, supplied, floor and grade, limiter, residual); - the gradient of a fixed weighting of the books on the state and the commands, by forward-mode duals. The test also checks that dyn_plant_books steps exactly as dyn_plant. DynBike.Golden and dyn_bike_golden.json are unchanged. nav_dyn_bike_test: 22 tests pass (MSVC 14.44 Release).
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…t slip in its wheel's frame (#138) Two commits, for Joe to review before merging: 1. a torch twin of libcvc's single-track vehicle in port-Hamiltonian form, with its per-step energy books; 2. `dyn_bike`'s front slip moved into its wheel's frame, following libcvc. They sit beside `dyn_plant` in `grl_snam/dyn_bike.py`. The whitepaper (#137, `docs/vehicle-ph-plant.tex` §8.2–8.3 and §10) lists the twin as missing. **1. The pH twin** (held to libcvc's `DynBikePH.Golden`, transfix/libcvc#848). New in `grl_snam/dyn_bike.py`, mirroring libcvc's `dyn_ph_*` in `cvc/nav/detail/dyn_bike.h`: - `dyn_ph_parts_at`: everything the form is built from at a state: - the axle forces (the port); - the tires' lateral forces and secant stiffnesses; - `u`, `sg`, `uf` and `Dx`; - the vectors `n_f`, `n_r`, `t_f`, `t_r`. - `dyn_ph_rates_at`: the power balance dH/dt = supplied − dissipated + floor + grade. - `dyn_ph_hamiltonian`: ½ vᵀMv. - `dyn_plant_books`: `dyn_plant`'s step, unchanged, plus its books: - the trapezoid of the rates between the step's start (with the actuators' outputs δ₁, a₁) and the twist the step reached before its limiters; - `limiter`: dH across the speed clamp and the low-speed blend; - `residual`: the rest. - `dyn_plant(..., with_free=True)` also returns the pre-limiter twist (libcvc's `dyn_step_free`). - `dyn_plant`'s step 2 moves into `_axles`, which the parts share. `tests/test_dyn_bike_ph_parity.py` checks the twin against `dyn_bike_ph_golden.json`, double tier, 1e-9 relative, on eight Humvee cases. Each case checks: - the parts and the rates; - one step's next state, pre-limiter twist and books; - the autograd gradient of a weighting of the books against libcvc's forward-mode duals. The file also tests that a batch books like its rows. A torch-only gate checks that the books close to second order on a swerve. **2. The wheel-frame front slip** (follows transfix/libcvc#852, approved by Joe). The front slip becomes the wheel-frame slip `dyn4`'s tires use: - alpha_f = −atan2(w_f, u_f); - w_f = cos δ (vy + lf r) − sin δ vx, which is n_f·v; - u_f is the floored forward speed in the wheel's frame; - the secant is rooted at w_f = 0. The implicit step's Jacobian takes the front tire's −S_f cos² δ (1, lf) on the body's y. In the pH twin, R's front term becomes S_f n_f n_fᵀ, and f_ε is round-off. Three fixtures are regenerated from libcvc#852: - `dyn_bike_golden.json`; - `dyn_bike_ph_golden.json`; - `material_ext_golden.json`: only its dynamic case changes; the surrogate and bicycle cases are byte-identical. **Measured** (torch 2.8, CPU, after both commits): - Worst relative difference from libcvc: | Values | Worst relative difference | |---|---| | Plant next state | 0 | | Plant gradient | 2.8e-16 | | pH parts | 3.4e-16 | | pH rates | 3.4e-16 | | Books | 7.1e-14 | | Books gradient | 4.4e-14 | - On the golden's cases, the floor power is at most 6e-13 W. - On the swerve, the mean |residual| per step falls 3.94× and then 3.97× per halving of the step. - `test_dyn_bike_parity`, `test_dyn_bike_ph_parity`, `test_material_ext_parity`, `test_dyn4_parity` and `test_material_bike_parity` give 57 passed and 6 skipped. The skips are live-pycvc checks that this machine's pycvc lacks. - ruff and black are clean on the changed files. pycvc has no dynamic binding, so none of this depends on a pycvc release.
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… 0) (#852) **Follows #848** (merged as 9b9270b; master is merged in, so the diff is the switch alone). The front slip of `dyn_bike` becomes the wheel-frame slip that `dyn_4w` uses (approved by Joe): alpha_f = -atan2(w_f, u_f) w_f = cos(delta) (vy + lf r) - sin(delta) vx (= n_fᵀ v, the front axle's sideways velocity in its wheel's frame) u_f = sqrt((cos(delta) vx + sin(delta) (vy + lf r))² + eps²) The front secant is now rooted at w_f = 0. Before, it was rooted at the floored speed's root, u tan(sg δ). The rear slip was already in its wheel's frame. The implicit step's Jacobian takes the front tire's d(F_yf cos δ)/d(vy, r) = −S_f cos² δ (1, lf), as `dyn_4w`'s does. **The pH form** - R's front term is S_f n_f n_fᵀ (it was (S_f / cos δ) n_f n_fᵀ). It is positive semi-definite at any δ. - f_ε is now round-off. The speed floor enters only the slips' forward speeds. The `floor` line stays in `dyn_ph_rates`, `dyn_ph_books` and `dyn_bike_books`, so their APIs don't change. - `dyn_ph_parts` gains `uf` and loses `w0f`. - `dyn_ph_tangent_D` takes the wheel-frame slip. Its front sensitivity is exact in (vy, r), including the forward speed's dependence, which runs along the same (1, lf). **Tests** (`nav_dyn_bike_test`, 23 tests) - `DynBikePH.TheFloorTermVanishesWithTheFloor` becomes `TheFloorTermIsRoundOff`. |floor power| / (dissipated + |supplied| + 1 W) is ≤ 2.2e-16 at every floor from 0.5 to 1e-9 m/s. Before, it was 5.35e-4 at 0.5 m/s. - New: `DynBikePH.TheTangentIsTheTiresDerivative` checks `dyn_ph_tangent_D` against central differences of the tires' lateral force and moment. Worst error: 1.4e-7 of its scale. - Three goldens are regenerated: - `DynBike.Golden`; - `DynBikePH.Golden` (the key `w0f` becomes `uf`); - `NavMaterialExt.Golden`'s dynamic case. Its surrogate and bicycle cases stay byte-identical. **Measured, before → after** (MSVC 14.44 Release) | Measure | Before | After | |---|---|---| | Kinematic-limit gap (`DynBike.KinematicLimitFollowsBikeStep`) | 0.01074 | 0.01074 | | Vector field vs plant, mu 0.9 / 0.6 | 1.62e-4 / 1.06e-4 m g | unchanged | | States past the peak | 244 of 500 per mu | unchanged | | Tangent bins | | unchanged to 0.1%: the front passes its peak from about 0.5 mu g; the rear never does | | Swerve: mean \|residual\| ratio per halving | 3.83 / 3.92 / 3.95 | unchanged | | Swerve: \|sum\| / flow at hdt 0.01 | 1.21e-3 | unchanged | | Braking to a stop, hdt 0.01: limiter / \|sum residual\| / flow | −353.5 J / 7.23e-7 | −358.2 J / 4.43e-6 | | Braking to a stop, hdt 0.005: limiter / \|sum residual\| / flow | −1.722 J / 1.72e-5 | −8.463 J / 1.76e-5 | | `physics_dyn_bike_plant_test`, Humvee: floor / residual share | 1.14 J / 1.10e-4 | −5.4e-15 J / 1.10e-4 | | `physics_dyn_bike_plant_test`, RoboRacer: residual share | 8.86e-4 | 8.88e-4 | | `nav_dyn_4w_test` single-track limit | 0.130 m / 0.016 m/s | unchanged | Also passing locally: | Suite | Tests | |---|---| | `nav_binding` | 6 | | `nav_dyn_4w` | 16 | | `nav_material_bike_rollout` | 12 | | `nav_material_ext` | 11 (with the regenerated golden) | | `physics_dyn_bike_plant` | 3 | | `physics_plant_host` | 5 | | `nav_sim_world` | 3 | `nav_plant`, `physics_plant_log`, `nav_coef_train` and `nav_potential` were still running when this was opened. GRL-SNAM follows in CVC-Lab/GRL-SNAM#138, which brings the torch `dyn_bike.py` and the three fixtures over. It matches the new goldens to 2.8e-16 on the plant and 7.1e-14 on the books. **Not changed:** `dyn_power.h`'s `dyn_tire_power` still uses the old front slip angle, sg δ − atan2(vy + lf r, u). Its tire-slip power therefore no longer reads the plant's own front slip. It wasn't part of the approved switch, and changing it moves the fitted power model, so it's left for a decision.
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The project version and the cvcpkg recipe family move to 3.7.2. Every recipe is at cvc_revision 1 already, so none restarts. 3.7.2 carries the dynamic plants on the terrain and in a Jolt world, and the four-wheel plant (#869): --plant dynamic and dynamic4w drive the ground, collide with the buildings and each other, and book the collisions. It also carries dyn_4w's port-Hamiltonian form (#850), dyn_bike's wheel-frame front slip (#852), the books goldens for GRL-SNAM's twins (#848, #849), pycvc's drive telemetry (#857) and keep-alives (#864), the macOS SDK's openssl (#846), and the state_exec scheduler and evaluator work (#842, #843, #844, #861, #863).
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A golden for
dyn_bike's port-Hamiltonian form (#831) and its per-step books, asDynBike.Goldenis for the plant. GRL-SNAM's torch twin ofdyn_ph_parts_at,dyn_ph_rates_atanddyn_plant_bookswill be held to it.TEST(DynBikePH, Golden)writessrc/cvc/tests/data/dyn_bike_ph_golden.jsonwhenCVC_DYN_BIKE_PH_GOLDEN_WRITE=1is set, and otherwise checks it to 1e-9 relative (the double tier).Cases. It uses
DynBike.Golden's Humvee (steering and drive lags, the low-speed blend) and its seven states: cruising, a hard corner, trail braking, past the tire's peak, backing up, creeping, and pulling away from rest. An eighth case brakes to a stop at the speed clamp, so the clamp's share of the limiter term is covered as well as the blend's.What each case records:
dyn_ph_parts_at):u,sg,Fxf,Fxr,Fyf,Fyr,wf,wr,w0f, the secantsSfandSr,Dx, andcd;dyn_ph_rates_at): dissipated, supplied, floor, and grade;dyn_plant_booksstep:dyn_step_free);g_books) with respect to the state and the commands, by forward-mode duals. The twin's gradient comes from autograd, so the two are independent derivations, as inDynBike.Golden.The test also checks that
dyn_plant_bookssteps exactly asdyn_plantdoes.DynBike.Goldenanddyn_bike_golden.jsonare unchanged.Locally (MSVC 14.44, Release):
nav_dyn_bike_testpasses all 22 tests,DynBike.Goldenincluded. clang-format 18 reports no changes on the changed lines.