Velocity-space distributions
Kinetic backgrounds
A kinetic background is the distribution f₀ a kinetic species starts from. It sets the initial marker sampling, appears in the numerator of the particle weights, and is subtracted off again in the control-variate method that keeps PIC noise down. Where a fluid equilibrium describes a background in space, these describe one in velocity — each in its own velocity coordinates.
CanonicalMaxwellian2D
Canonical Maxwellian distribution function in (η₁, η₂, η₃, v∥, μ) coordinates.
No velocity space
ColdPlasma
Base class for a distribution as a Dirac-delta in velocity (vth = 0).
GyroMaxwellian2D
A gyrotropic Maxwellian depending on two velocities (v∥, μ), n=2, where v∥ = 𝐯 · b₀ and μ = v⟂²/(2B₀) is the magnetic moment, with B₀ the background magnetic field strength.
GyroMaxwellian2Dvperp
A gyrotropic Maxwellian depending on two velocities (v∥, v⟂), n=2, where v∥ = 𝐯 · b₀ and v⟂ is the radial component of a polar coordinate system perpendicular to the magentic direction b₀.
Maxwellian3D
A Maxwellian depending (η₁, η₂, η₃) and on three (n=3) Cartesian velocities.
How these are sampled
Every plot on these pages is evaluated through struphy's own reduced_eval, which integrates the distribution over the phase-space axes that are not shown. Velocity space is sampled at the fixed logical point η = (0.5, 0.5, 0.5); that choice only matters for backgrounds whose moments vary in space, but it keeps the plots comparable across classes. Each class is shown with its constructor defaults, so a background that looks symmetric here can still be shifted or sheared by the moments you give it in a parameter file.