Configuration cards

Writing configuration cards

PineAPFEL uses YAML configuration files to specify all physics and numerical parameters. The theory card and operator card are required for both grid creation and evolution. An additional grid card is needed when creating grids with build_grid() or pineapfel-build (see Grid creation for the full grid card reference).

Theory card

# Initial evolution scale in GeV.
mu0: 1.0

# QCD perturbative order:
#   0 = LO
#   1 = NLO
#   2 = NNLO
PerturbativeOrder: 2

# Reference scale for alpha_s in GeV.
QRef: 91.1876

# Value of alpha_s(Q_ref)
AlphaQCDRef: 0.118

# Quark mass thresholds in GeV, one per active flavor.
# Ordering: up, down, strange, charm, bottom.
# Use 0.0 for massless quarks. The length determines the maximum number
# of active flavors (nf_max).
QuarkThresholds: [0.0, 0.0, 0.0, 1.4, 4.75]

# Physical heavy-quark masses for massive coefficient functions, all 6
# flavors required (up, down, strange, charm, bottom, top) in GeV.
# Used when MassScheme: FFN or MassScheme: FONLL is set in the grid card.
# Defaults to QuarkThresholds padded to 6 entries (top = 172.0 GeV) if absent.
HeavyQuarkMasses: [0.0, 0.0, 0.0, 1.4, 4.75, 172.0]

# CKM squared matrix elements |Vij|^2, 9 entries in row-major order:
# [Vud^2, Vus^2, Vub^2, Vcd^2, Vcs^2, Vcb^2, Vtd^2, Vts^2, Vtb^2]
# Only used for CC grids. Optional: defaults to standard PDG values if absent.
CKM: [0.94922, 0.05077, 0.00001, 0.05073, 0.94760, 0.00168, 0.00007, 0.00162, 0.99831]

# Output flavor PIDs written to the FK table.
# These define the pids_out dimension of the evolution operator.
# Standard PDG codes: 1=d, 2=u, 3=s, 4=c, 5=b, -1=dbar, ..., 21=gluon, 22=photon
Flavors: [-5, -4, -3, -2, -1, 1, 2, 3, 4, 5, 21]

# --- Massive coefficient function tabulation parameters ---
# These control the xi = Q^2/m^2 interpolation grid built by APFEL++ when
# MassScheme: FFN or MassScheme: FONLL is set in the grid card.
# All fields are optional; the values shown are the defaults.

# Number of xi interpolation points.
MassNxi: 150

# xi range [MassXiMin, MassXiMax] over which massive CFs are tabulated.
MassXiMin: 0.05
MassXiMax: 10000.0

# Polynomial interpolation degree in xi.
MassIntDeg: 3

# Lambda parameter for the xi-grid density (controls spacing near xi = 0).
MassLambda: 0.0005

# Interpolation mode passed to TabulateObject (0 = default).
MassIMod: 0

# Set to true to use combined QCD+QED evolution.
# When false (default), pure QCD evolution is used.
QED: false

# --- QED-specific fields (ignored when QED: false) ---

# Value of alpha_em at the reference scale
AlphaQEDRef: 0.00729927

# Lepton mass thresholds in GeV.
# Leave empty to forbid lepton creation during evolution.
LeptonThresholds: []

Operator card

# x-space interpolation grid.
# Each sub-grid is defined by:
#   n_knots:     number of interpolation knots
#   x_min:       lower edge of the sub-grid in Bjorken x
#   poly_degree: polynomial interpolation degree
#
# The sub-grids are joined into a single APFEL++ Grid object.
xgrid:
  - n_knots: 80
    x_min: 1.0e-5
    poly_degree: 3
  - n_knots: 40
    x_min: 1.0e-1
    poly_degree: 3

# Tabulation parameters for the running coupling(s).
# These are passed to the apfel::TabulateObject constructor:
#   n_points:     number of interpolation points
#   q_min:        minimum scale in GeV for the tabulation
#   n_steps:      number of steps in the tabulation grid
#   interp_degree: interpolation degree for the tabulated object
tabulation:
  n_points: 200
  q_min: 0.9
  n_steps: 13001
  interp_degree: 3

# Scale variation factors: [xi_R, xi_F, xi_A]
# Use [1.0, 1.0, 1.0] for central predictions.
xi: [1.0, 1.0, 1.0]

# --- Optional: SIDIS grid filling only ---
# Omit these for DIS/SIA-only workflows.
#
# sidis_mode: legacy | bsf_exact
# sidis_int_eps: <double>   # APFEL++ InitializeSidisObjects tolerance (default 1e-3)

SIDIS-only YAML fields

These keys are parsed into pineapfel::OperatorCard and affect build_grid() only when the grid card has Process: SIDIS.

YAML key	C++ default (if omitted)	Purpose
`sidis_mode`	`legacy`	`legacy` = Gauss–Legendre \(z\) quadrature in each \(z\) bin; `bsf_exact` = APFEL++-style \(z\) weights (`IntInterpolant`) for extended \(z\) bins.
`sidis_int_eps`	`1e-3`	Relative tolerance for `InitializeSidisObjects` / SIDIS NNLO setup (tests often use `1e-1`).

See Grid creation — Operator card: SIDIS-only settings for details.