Densities #
Ported from scottnarmstrong/Superdiffusion at 7f20476385d4af418f110303085ad0740c9eba46. Module imports, support namespace and local option directives adapted for Lean Pool.
Path densities for the coefficient perturbation a + t h #
Along the canonical perturbation path t ↦ perturbCoeffOn U a h t the doubled
energy density of a fixed doubled field expands exactly in t:
E_t(X)(x) = E_0(X)(x) + t · L(X)(x) + t² · Q(X)(x)
with the linear density L(X) = -(h X₁)·(bfA(a) X)₂ and the quadratic density
Q(X) = ½ (h X₁)·s⁻¹(h X₁). This module defines the two densities, proves
the a.e. expansion from the pointwise algebra in PointwiseExpansion, and
establishes the L¹ integrability needed to pass to averaged values.
Averages only see the a.e. class of the integrand.
The canonical path through the frozen perturbation #
The frozen perturbation body evaluated at a point.
At t = 0 the canonical path starts at the base field, up to a null set.
The linear and quadratic path densities #
Linear-response density of a doubled field along the path: the exact
cross term -(h X₁) · (bfA(a) X)₂ produced by the shear conjugation.
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Quadratic-response density of a doubled field along the path:
½ (h X₁) · s⁻¹ (h X₁).
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Averaged linear-response term.
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Averaged quadratic-response term.
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The exact pointwise and a.e. expansions along the path #
Exact expansion of the doubled energy density along the canonical path at a point where the perturbation is skew.
The a.e. exact expansion of the doubled energy density of a doubled field along the canonical path.
Square integrability of the block image of an L² doubled field #
The second block component of bfA(a) X is vector L² when the doubled
field has vector L² components.
The first block component of bfA(a) X is vector L² when the doubled
field has vector L² components.
Applying the a.e. inverse of the symmetric part preserves vector L².
Memberships from mu-admissibility #
The potential component of a mu-admissible doubled field is vector L².
The flux component of a mu-admissible doubled field is vector L².
Integrability of the densities #
The base doubled energy density of an L² doubled field is integrable.
The linear path density is integrable for L² doubled fields and L∞
perturbations.
The quadratic path density is integrable for L² doubled fields and L∞
perturbations.