qlat.fermion_action — Fermion Action Parameters for Domain-Wall Fermions

Source: qlat/qlat/fermion_action.py

Note: Update this document when updating the source file.

Outline

  1. Overview

  2. FermionAction Class

  3. Examples

Overview

fermion_action provides the FermionAction class, which encapsulates the parameters of a domain-wall fermion action. Two variants are supported:

  • Mobius — a single mobius_scale parameter controls the extent of the fifth dimension. This is the standard formulation used in most lattice QCD simulations with domain-wall fermions.

  • ZMobius — an explicit list of omega coefficients replaces the uniform Mobius scale, allowing finer control over the approximation to the sign function in the fifth dimension.

The class manages the lifetime of a C++ FermionAction object through the cdata attribute and the qlat.c backend.

FermionAction Class

Constructor

FermionAction(*, mass: float, ls: int, m5: float,
              mobius_scale: float = 1.0, omega: list = None)

Create a fermion action descriptor. If omega is None, a standard Mobius action is created. If omega is provided (a list of length ls), a ZMobius action is created instead.

Parameter

Type

Default

Description

mass

float

—

Quark mass

ls

int

—

Extent of the fifth dimension

m5

float

—

Domain-wall height (typically 1.0–1.8)

mobius_scale

float

1.0

Mobius scale parameter (Mobius variant only)

omega

list[float] or None

None

ZMobius coefficients; must have length ls

Raises: AssertionError if parameter types are incorrect, or if len(omega) != ls for the ZMobius variant.

Attribute Accessors

mass()

mass() -> float

Return the quark mass.

ls()

ls() -> int

Return the extent of the fifth dimension.

m5()

m5() -> float

Return the domain-wall height.

omega()

omega() -> list[float]

Return the ZMobius omega coefficients. For a standard Mobius action this returns the uniform omega values derived from mobius_scale.

mobius_scale()

mobius_scale() -> float

Return the Mobius scale parameter.

Assignment

__imatmul__ (@=)

fa1 @= fa2

Copy the contents of fa2 into fa1. Both must be FermionAction instances. This delegates to qlat.c.set_fermion_action.

Examples

Create a Mobius Fermion Action

import qlat as q

size_node_list = [
    [1, 1, 1, 1],
]

q.begin_with_mpi(size_node_list)

fa = q.FermionAction(mass=0.01, ls=24, m5=1.8, mobius_scale=2.0)

print(f"mass = {fa.mass()}")
print(f"ls   = {fa.ls()}")
print(f"m5   = {fa.m5()}")
print(f"mobius_scale = {fa.mobius_scale()}")

q.end_with_mpi()

Create a ZMobius Fermion Action

import qlat as q

size_node_list = [
    [1, 1, 1, 1],
]

q.begin_with_mpi(size_node_list)

omega = [0.5 + 0.1 * i for i in range(12)]
fa = q.FermionAction(mass=0.01, ls=12, m5=1.8, omega=omega)

print(f"mass  = {fa.mass()}")
print(f"ls    = {fa.ls()}")
print(f"m5    = {fa.m5()}")
print(f"omega = {fa.omega()}")

q.end_with_mpi()

Copy a Fermion Action

import qlat as q

size_node_list = [
    [1, 1, 1, 1],
]

q.begin_with_mpi(size_node_list)

fa1 = q.FermionAction(mass=0.01, ls=24, m5=1.8, mobius_scale=2.0)
fa2 = q.FermionAction(mass=0.08, ls=16, m5=1.0, mobius_scale=1.0)

fa2 @= fa1
print(f"fa2 mass = {fa2.mass()}")  # 0.01
print(f"fa2 ls   = {fa2.ls()}")    # 24

q.end_with_mpi()