Solver Options

Solver Options

Termination and stepping options live in LobContext and are set via the builder. All default to “off” unless noted — the solver then uses its 1-yard Heun grid and runs to the last requested range unless another stop fires. (max_time defaults to NaN for “no limit”; see below.)

Step size

• Builder: StepSize(uint16_t inches) / LobBuilderStepSize
• Context: step_size inches, 0 = default 1 yard (36 in)
• Code: source/solve_step.cpp SolveStep — Δx = min(target−x, step_size) (last step clamped), Heun k1+k2 + trapezoidal TOF += 2·Δx/(vx_old+vx_new).

Smaller Δx reduces truncation error monotonically; benchmark/ode.cpp shows linear cost in 1/Δx. Default 1 yd meets the validation_overview tolerances out to 1000 yd — tighten only when you need it and can pay for it.

Maximum time

• Builder: MaximumTime(double seconds) — ≥ 0 else kMaximumTimeOOR
• Context: max_time seconds, NaN = no limit (builder leaves NaN, BuildOptions checks <0 only)
• Solver: source/lob_solve.cpp LobSolve — if s.TOF ≥ max_time and previous < max_time, the last Output is linearly interpolated to max_time via LerpOutput. No further ranges are attempted.

Minimum speed / energy

• Builder: MinimumSpeed(uint16_t fps), MinimumEnergy(uint16_t ft·lbf)
• Context: minimum_speed fps — BuildOptions (source/lob_builder.cpp) computes speed_from_energy = CalculateVelocityFromKineticEnergy(minimum_energy, mass) (source/calc.hpp) and stores max(explicit, from_energy).
• Solver: if |v| ≤ minimum_speed and previous > minimum_speed, last Output is interpolated to that speed (source/lob_solve.cpp). Both are floors — whistling past either stops the trajectory.

max_time, minimum_speed, minimum_energy, and tumble are forward-stop “stop and interpolate” conditions: the output at the stop is a LerpOutput between the two Heun steps straddling the limit, and LobSolve returns only up to that point. Any of those stops may therefore shorten kForwardSolves independently of angle solving. Separately, LobSolveInverse stops when SolveAngle returns NaN for an unreachable angle (Inverse Solve).

Optic and zero helpers

• OpticHeightInches(double) — feet internally (FeetT(InchT(...))), default 1.5 in (source/lob_builder.cpp BuildOpticHeight).
• ZeroAngleMOA vs ZeroDistanceYds (+ ZeroImpactHeightInches) — exactly one is required; the distance path is solved via the shared angle solver (Zero-Angle Solver, Shared Angle Solver) with vacuum-parabola seed 0.5·g·R/v0² clamped to ±45°.
• RangeAngleDeg — inclination, gravity rotated gx=−g·sin, gy=−g·cos (source/lob_builder.cpp BuildEnvironment); validated |angle| < 90°.

Atmosphere, wind, Coriolis

• Atmosphere inputs (AltitudeOfFiringSiteFt, AirPressureInHg, AltitudeOfBarometerFt, TemperatureDegF, AltitudeOfThermometerFt, RelativeHumidityPercent) only affect speed_of_sound and drag_coeff at Build() time — see Atmospheric Model.
• Wind (WindHeading/WindHeadingDeg + WindSpeed*) only enters as v−w in DsDx and w_z in jump — see Wind and Coriolis.
• Coriolis needs both AzimuthDeg and LatitudeDeg; otherwise zeroed.

None of these allocate; Context is self-contained after Build() (Context and Results).