Imports
/- Copyright (c) 2026 Lazar Milikic. All rights reserved. Released under Apache 2.0 license as described in the file LICENSE. Authors: Lazar Milikic -/ module public import Physlib.SpaceAndTime.Space.Norm.Basic

Iterated Laplacians of norm distributions

i. Overview

This file proves the distributional identity corresponding to the classical odd-dimensional formula that, in dimension 2 * m + 1, applying the Laplacian m + 1 times to the norm gives a nonzero constant multiple of the Dirac delta at the origin.

ii. Key results

    iterated_distLaplacian_norm_zpow_odd_eq_smul_diracDelta : The (m + 1)-fold Laplacian of the norm in dimension 2 * m + 1 is a nonzero multiple of the Dirac delta.

iii. Table of contents

    A. The odd-dimensional iterated Laplacian of the norm

iv. References

@[expose] public section

A. The odd-dimensional iterated Laplacian of the norm

m:ℕk:ℕhk:k < mh:1 - 2 * ↑k - 2 + (2 * ↑m + 1) ≠ 0⊢ ↑(1 - 2 * ↑k - 2 + (2 * ↑m + 1)) ≠ 0 All goals completed! 🐙

The scalar factor in the odd-dimensional iterated Laplacian of the norm is nonzero.

m:ℕh:1 - 2 * ↑m ≠ 0⊢ ↑1 - 2 * ↑↑m ≠ 0 All goals completed! 🐙 m:ℕ⊢ 2 * ↑m + 1 ≠ 0 exact_mod_cast (m:ℕ⊢ 2 * m + 1 ≠ 0 All goals completed! 🐙 : (2 * m + 1 : ℕ) ≠ 0) m:ℕ⊢ volume.real (Metric.ball 0 1) ≠ 0 All goals completed! 🐙
⊢ distDiv (distOfFunction (fun x => (↑1 * ‖x‖ ^ (1 - 2)) • basis.repr x) ⋯) = ((↑1 - 2 * ↑↑0) * (2 * ↑0 + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 ⊢ distDiv (distOfFunction (fun x => ‖x‖ ^ (1 - 2) • basis.repr x) ⋯) = ((1 - 2 * ↑↑0) * (2 * ↑0 + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 ⊢ ((1 - 2 * ↑↑0) * (2 * ↑0 + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 = (↑1 * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 ⊢ ((1 - 2 * ↑↑0) * (2 * ↑0 + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 = (↑1 * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 x:𝓢(Space (2 * 0 + 1), ℝ)⊢ (((1 - 2 * ↑↑0) * (2 * ↑0 + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0) x = ((↑1 * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0) x All goals completed! 🐙 m:ℕ⊢ Δᵈ (distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑(m + 1))) ⋯) = ((↑1 - 2 * ↑↑(m + 1)) * (2 * ↑(m + 1) + 1) * volume.real (Metric.ball 0 1)) • diracDelta ℝ 0 m:ℕx✝:Space (2 * (m + 1) + 1)⊢ ‖x✝‖ ^ (1 - 2 * ↑(m + 1)) = ‖x✝‖ ^ (-(↑(2 * m.succ + 1) - 2))m:ℕ⊢ ↑1 - 2 * ↑↑(m + 1) = -(↑(2 * m.succ + 1) - 2)m:ℕ⊢ 2 * ↑(m + 1) + 1 = ↑(2 * m.succ + 1) m:ℕx✝:Space (2 * (m + 1) + 1)⊢ ‖x✝‖ ^ (1 - 2 * ↑(m + 1)) = ‖x✝‖ ^ (-(↑(2 * m.succ + 1) - 2)) m:ℕx✝:Space (2 * (m + 1) + 1)⊢ ‖x✝‖ ^ (1 - 2 * (↑m + 1)) = ‖x✝‖ ^ (2 - (2 * (↑m + 1) + 1)); All goals completed! 🐙 m:ℕ⊢ ↑1 - 2 * ↑↑(m + 1) = -(↑(2 * m.succ + 1) - 2) m:ℕ⊢ 1 - 2 * (↑m + 1) = 2 - (2 * (↑m + 1) + 1); All goals completed! 🐙 m:ℕ⊢ 2 * ↑(m + 1) + 1 = ↑(2 * m.succ + 1) All goals completed! 🐙m:ℕk:ℕih:∀ (hk : k ≤ m), (⇑Δᵈ)^[k] (distOfFunction (fun x => ‖x‖ ^ 1) ⋯) = (∏ j ∈ Finset.range k, ↑(1 - 2 * ↑j) * ↑(1 - 2 * ↑j - 2 + (2 * ↑m + 1))) • distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑k)) ⋯hk:k + 1 ≤ mhk_le:k ≤ mhdist:distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑k - 2)) ⋯ = distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑(k + 1))) ⋯⊢ ((∏ j ∈ Finset.range k, ↑(1 - 2 * ↑j) * ↑(1 - 2 * ↑j - 2 + (2 * ↑m + 1))) * (↑(1 - 2 * ↑k) * ↑(1 - 2 * ↑k - 2 + ↑(2 * m + 1)))) • distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑(k + 1))) ⋯ = ((∏ x ∈ Finset.range k, ↑(1 - 2 * ↑x) * ↑(1 - 2 * ↑x - 2 + (2 * ↑m + 1))) * (↑(1 - 2 * ↑k) * ↑(1 - 2 * ↑k - 2 + (2 * ↑m + 1)))) • distOfFunction (fun x => ‖x‖ ^ (1 - 2 * ↑(k + 1))) ⋯ All goals completed! 🐙

In dimension 2 * m + 1, the (m + 1)-fold distributional Laplacian of the distribution induced by the norm is a nonzero multiple of the Dirac delta at the origin.

m:ℕ⊢ ((∏ j ∈ Finset.range m, ↑(1 - 2 * ↑j) * ↑(1 - 2 * ↑j - 2 + (2 * ↑m + 1))) * ((↑1 - 2 * ↑↑m) * (2 * ↑m + 1) * volume.real (Metric.ball 0 1))) • diracDelta ℝ 0 = oddNormIteratedLaplacianCoeff m • diracDelta ℝ 0 m:ℕ⊢ ((∏ j ∈ Finset.range m, ↑(1 - 2 * ↑j) * ↑(1 - 2 * ↑j - 2 + (2 * ↑m + 1))) * ((↑1 - 2 * ↑↑m) * (2 * ↑m + 1) * volume.real (Metric.ball 0 1))) • diracDelta ℝ 0 = ((∏ k ∈ Finset.range m, ↑(1 - 2 * ↑k) * ↑(1 - 2 * ↑k - 2 + (2 * ↑m + 1))) * ((↑1 - 2 * ↑↑m) * (2 * ↑m + 1) * volume.real (Metric.ball 0 1))) • diracDelta ℝ 0 All goals completed! 🐙