API Reference

Estimate initial orbital parameters.

SimulationSupport.EccentricityControl.InitialOrbitalParameters.initial_orbital_parameters(target_params, separation=None, orbital_angular_velocity=None, radial_expansion_velocity=None)

Estimate initial orbital parameters from a Post-Newtonian approximation.

Given the target eccentricity and one other orbital parameter, this routine estimates the initial separation D, orbital angular velocity Omega_0, and radial expansion velocity adot_0 for a binary system. The resulting parameters can be fed into an eccentricity control loop to refine the starting parameters.

Parameters:

• target_params (dict) –

  Simulation parameters that describe the binary. The dictionary must include the following keys:

  • "MassRatio": Mass ratio \(q = M_A / M_B \ge 1\).

  • "DimensionlessSpinA": Dimensionless spin vector of the larger black hole (length 3).

  • "DimensionlessSpinB": Dimensionless spin vector of the smaller black hole (length 3).

  • "Eccentricity": Target orbital eccentricity. Provide this value together with exactly one of the orbital parameters below.

  Optional keys:

  • "MeanAnomalyFraction": Mean anomaly divided by \(2\pi\) (between 0 and 1). Required for nonzero eccentricity.

  • "NumOrbits": Desired number of inspiral orbits until merger.

  • "TimeToMerger": Desired time to merger.

• separation (float, optional) – Coordinate separation D of the black holes.

• orbital_angular_velocity (float, optional) – Orbital angular velocity Omega_0.

• radial_expansion_velocity (float, optional) – Radial expansion velocity adot_0.

Returns:

A tuple (D_0, Omega_0, adot_0) with the initial separation, orbital angular velocity, and radial expansion velocity.

Return type:

tuple[float, float, float]