Trilinear Hilbert transform: sep_one_atom_expansion #
Blueprint lem:separation, lines 1402–1407 (first part): the exact separation of
one atom in slot i along the other slots a, b and the time variable. The atom is
a finite sum over bounded carries of absolutely convergent series of products of
three chart atoms with matrices -α_a C, -α_b C, S C.
An atom whose amplitude is a modulated plateau cutoff of radius 3/4 is bounded
by 6^d, uniformly in the modulation and all phase parameters.
The separation coefficients are absolutely summable.
One term of the one-atom separation series.
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Blueprint lem:separation, line 1407: two atoms in distinct slots i, k are
separated along the remaining slots a, b and the time variable; their product is
an absolutely convergent series of products of separated factor atoms.
Normalizing a chart whose atom is bounded by M > 0 to a bounded atom.
The bounded slot-a factor of a separated pair.
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The bounded slot-b factor of a separated pair.
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The bounded time factor of a separated pair.
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The factors of a separated pair are bounded atoms.
Blueprint lem:separation, eq:separation: the exact expansion
φ_i(y_i) φ_k(y_k) = Σ c ψ_a(y_a) ψ_b(y_b) Q(t) with bounded factor atoms.
Quantitative bounds for the separated terms #
The three coordinate blocks of ℝ^(d+d+d) as continuous linear maps.
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- TrilinearHT.Auto.tripleFstCLM d = ContinuousLinearMap.pi fun (l : Fin d) => ContinuousLinearMap.proj (Fin.castAdd d (Fin.castAdd d l))
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Continuous linear projection onto the middle block of three coordinate blocks.
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- TrilinearHT.Auto.tripleSndCLM d = ContinuousLinearMap.pi fun (l : Fin d) => ContinuousLinearMap.proj (Fin.castAdd d (Fin.natAdd d l))
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Continuous linear projection onto the last block of three coordinate blocks.
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- TrilinearHT.Auto.tripleThdCLM d = ContinuousLinearMap.pi fun (l : Fin d) => ContinuousLinearMap.proj (Fin.natAdd (d + d) l)
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Geometric bounds for a chart amplitude from its complexity.
lem:separation, line 1407: explicit geometric derivative bounds of the coupled amplitude, from the chart complexity, the plateau and the partition Gevrey bounds.
lem:separation, line 1407: coefficient envelope and shell masses of the
separation coefficients, with the integration-by-parts order exceeding the
Fourier dimension 3d by q + 1.
The coupled-amplitude derivative budget is a power of any common bound W
of its parameters, with exponent linear in the order.
lem:separation, line 1407: the shell masses of the separation coefficients
are at most exp(D X^D) T^{-q} and their total mass at most exp(D X^D), where
X = 1 + log H and D depends only on the fixed Gevrey orders, q and the slot gaps.
Heights of products of rationals.
Higher derivatives of a real affine function are bounded by powers of its linear part.
The linear modulation phase w ↦ Σ_l p_l w_l / L as a continuous linear functional.
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- TrilinearHT.Auto.modulationFunctional L p = ∑ l : Fin d, (↑(p l) / L) • ContinuousLinearMap.proj l
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Geometric derivative bounds for a modulated plateau cutoff.
lem:separation, line 1407: complexity of a modulated-cutoff chart at Gevrey order
2Kψ. The parameter W must dominate the dimension, matrix heights, support and the
first-order derivative scale.
A one-dimensional chart whose atom is identically one, at a fixed Gevrey order.
Padding a chart to positive dimension without changing its atom.
The fixed constant in the factor-chart complexity bound of lem:separation.
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lem:separation, line 1407: a factor chart ψ_p with matrix q C has complexity
at most W at Gevrey order 2Kψ whenever W ≥ K Q² H² (1 + Σ_l |p_l|), where Q
bounds the height of the fixed rational q.
lem:separation, line 1407: complexity of the three factor charts of one separated atom.
lem:separation, line 1407: the normalized bounded factors of a separated pair have
complexity at most W⁶ at the fixed Gevrey order 2Kψ, where
W ≥ K Q² H² (1 + Σ|p_l| + Σ|p'_l|).
Separated forms: the kernel expansion and the Fourier supremum bound #
Coordinate-line derivatives of a cube periodization.
The derivative constant of the admissible kernel class at order m.
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- TrilinearHT.Auto.kernelDerivBound κ m = (κ.derivativeConstant * (↑m + 2)) ^ (κ.derivativeConstant * (↑m + 2))
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The uniform absolute Fourier mass of admissible kernels.
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lem:separation, line 1409: an admissible kernel has an absolutely convergent
two-variable Fourier expansion near its cell, with absolute coefficient mass
bounded uniformly over the kernel class. Only pure x- and t-derivatives enter.
Integrability of a pair of L¹ ∩ L² inputs along two distinct progression slots.
Fubini and the change of variables to a correlation along two progression slots.
lem:separation, line 1409: one modulated separated term is bounded by r A_r times
the L² norms of its two inputs supported in the cell.
lem:separation, line 1409: the separated single-scale form r⁻² ∫ w Q(t) F_a(y_a) F_b(y_b)
in two distinct slots is bounded by C A_r times the normalized L²(I) norms, where
A_r ≤ M bounds sup_ξ |∫ Q(ru) ζ(u) e(-ξu) du| and C depends only on the kernel class.
The separated phase (lem:separation, line 1411) #
A rational matrix acting as an orthogonal projection is symmetric.
The isotropy of the fast subspace as a matrix identity.
A one-variable chart regarded as a chart in one real variable.
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The Fourier transform on ℝ¹ of a function of the single coordinate.
Height of the separated phase matrix: quasipolynomial in the heights of C and Q.
Blueprint lem:separation, eq:separated-phase (line 1411): if the Fourier supremum
A_r of a time chart is at least δ, then on the scale-r window
Q(t) = e(λ_* t² + β t) Σ a_ℓ e(σ_ℓ·θ t) exactly and absolutely, with
λ_* = λ + θᵀ M θ for a rational matrix M of bounded height, |λ_*| r² ≤ D, and
rational frequencies σ_ℓ of height ≤ D(1+|ℓ|) and the shell bounds of lem:chartfourier;
everything is quasipolynomial in H and δ⁻¹.
Uniform separated approximation of the kernel (lem:separation, line 1411) #
A smooth function on ℝ² supported in [-4,4]² with coordinate-line derivative bounds
has an absolutely convergent Fourier expansion on [-8,8]² with explicit coefficient decay.
The admissible kernel times the chirp e(Λ u₁²), at unit scale.
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- TrilinearHT.Auto.chirpedKernelRescale a₀ r Λ w u = TrilinearHT.Auto.kernelUnitRescale a₀ r w u * ↑(Real.fourierChar (Λ * u 1 ^ 2))
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Cumulative derivative constant of the kernel class up to order m.
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- TrilinearHT.Auto.kernelDerivSum κ m = ∑ i ∈ Finset.range (m + 1), TrilinearHT.Auto.kernelDerivBound κ i
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The coordinate-line derivative constant of the chirped kernel.
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The constant of the chirped kernel's Fourier tail at order three.
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lem:separation, line 1411 (core): with a time-chart expansion
e(-Λ(t/r)²) Q(t) = Σ a_p e(γ_p t) on the window and the chirped kernel expansion,
the kernel w(x,t) Q(t) on I × I is approximated by a finite double sum of
pure linear phases in (x,t), with explicit truncation errors.
The fixed constant of the chirped kernel tail (depends only on the kernel class).
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The fixed constant of the chirped kernel bounds (depends only on the kernel class).
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Total Fourier mass of the chirped kernel.
Blueprint lem:separation, line 1411: if A_r ≥ δ, the two-variable kernel
w(x,t) Q(t) on I × I (with t = (y_b - y_a)/(b - a), x = y_a - a t) has a uniform
ε-approximation by a finite sum Σ c_ν e(α_ν y_a) e(β_ν y_b) of products of bounded
atoms (pure linear phases), with number of terms and absolute coefficient norm
quasipolynomial in H, δ⁻¹, ε⁻¹.
Packaging lem:separation: coefficient tails of the separated pair #
Shell bounds with decay T^{-q} give the pooled tail 2E/2^{Kq} past 2^K.
Tail mass past an arbitrary level T ≥ 1 from shell bounds of decay T^{-q}.
Mass and tail of a product of two coefficient families.
The normalized coefficient family of one separated atom: total mass and tails
(lem:separation, line 1407), quasipolynomial in H.