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Project-declaredLean 4.32.0 · mathlib@81a5d257c8e4

Dist Laplacian fundamental Solution norm zpow

Space.distLaplacian_fundamentalSolution_norm_zpow

Plain-language statement

The distributional Laplacian of ‖x‖ ^ (2 - d) is (2 - d) * d * volume (Metric.ball 0 1) times the Dirac delta at the origin. For d ≥ 3 this ‖x‖ ^ (2 - d) is the (singular) fundamental solution of the Laplacian, and for d = 1 it is ‖x‖. When d = 2 the exponent vanishes, so the identity collapses to the trivial Δᵈ 1 = 0; the genuine two-dime...

Exact Lean statement

lemma distLaplacian_fundamentalSolution_norm_zpow {d : ℕ} :
    Δᵈ (distOfFunction (fun x : Space d => ‖x‖ ^ (- ((d : ℤ) - 2)))
      (IsDistBounded.pow _ (by omega))) =
      ((- ((d : ℝ) - 2)) * d *
        (volume (α := Space d)).real (Metric.ball 0 1)) • diracDelta ℝ 0

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
lemma distLaplacian_fundamentalSolution_norm_zpow {d : } :    Δᵈ (distOfFunction (fun x : Space d => ‖x‖ ^ (- ((d : ) - 2)))      (IsDistBounded.pow _ (by omega))) =      ((- ((d : ) - 2)) * d *        (volume (α := Space d)).real (Metric.ball 0 1)) • diracDelta  0 := by  by_cases h : d = 0  · subst h    have hzero :        distOfFunction (fun x : Space 0 => ‖x‖ ^ 2)          (IsDistBounded.pow _ (by omega)) = 0 := by      ext η      rw [distOfFunction_apply]      refine integral_eq_zero_of_ae (ae_of_all _ fun x => ?_)      rw [Subsingleton.elim x 0]      simp [zero_zpow_eq]    simp [hzero]  · haveI : NeZero d := by omega    rw [distLaplacian]    change ∇ᵈ ⬝ (∇ᵈ (distOfFunction      (fun x : Space d => ‖x‖ ^ (- ((d : ) - 2)))      (IsDistBounded.pow (- ((d : ) - 2)) (by omega)))) = _    rw [distGrad_distOfFunction_norm_zpow (- ((d : ) - 2)) (by omega)]    simp only [neg_sub, Int.cast_sub, Int.cast_ofNat, Int.cast_natCast, sub_sub_cancel_left]    have hdist :        distOfFunction          (fun x : Space d =>            ((2 - (d : )) * ‖x‖ ^ (- (d : ))) • basis.repr x)          (by            simpa [smul_smul] using              (IsDistBounded.const_fun_smul                (F := EuclideanSpace  (Fin d))                (IsDistBounded.zpow_smul_repr_self (- (d : )) (by omega))                (2 - (d : )))) =          (2 - (d : )) • distOfFunction            (fun x : Space d =>              ‖x‖ ^ (- (d : )) • basis.repr x)            (IsDistBounded.zpow_smul_repr_self (- (d : )) (by omega)) := by      convert distOfFunction_smul_fun        (fun x : Space d =>          ‖x‖ ^ (- (d : )) • basis.repr x)        (IsDistBounded.zpow_smul_repr_self (- (d : )) (by omega))        (2 - (d : )) using 1      ext x      simp [smul_smul]    rw [hdist, map_smul, distDiv_inv_pow_eq_dim, smul_smul]    ring_nf
Project
Physlib
License
Apache-2.0
Commit
dd43e9e65791
Source
Physlib/SpaceAndTime/Space/Norm/Basic.lean:1083-1128

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Plain-language statement

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physicsquantum field theoryrelativity

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Person-level attribution pending.

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Project-declaredLean 4.32.0

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Plain-language statement

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Source project: Physlib

Person-level attribution pending.

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