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LeanPool.Superdiffusion.Algsuperdiff.Section24.Sensitivity.Provider.Path.Densities

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.

The canonical path through the frozen perturbation #

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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      The exact pointwise and a.e. expansions along the path #

      Square integrability of the block image of an L² doubled field #

      Memberships from mu-admissibility #

      Integrability of the densities #