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Weighted coordinate norm and its reduction to a plain coordinate norm

Definition
HlawkaSchatten_DiagonalConstruction_WeightedCoordinates

by savarin · Sep 28, 2026 · Mathlib 0df444a (Lean v4.33.1)

concavitydiagonal-constructionhlawka-schattenlp-normweighted-norm

Two total definitions describe weighted coordinate power functionals for real ppp and real vectors indexed by an arbitrary finite type. In the positive-exponent range, nonnegative weights can be absorbed into a rescaling of the coordinates. The ordinary unweighted functional is a norm in the range p≥1p\ge1p≥1.

weightedNorm attaches a real weight wiw_iwi​ (nonnegative in use) to each coordinate before summing:

weightedNorm⁡(p,x,w)=(∑iwi ∣xi∣p)1/p.\operatorname{weightedNorm}(p,x,w) = \Big(\sum_i w_i\,|x_i|^p\Big)^{1/p}.weightedNorm(p,x,w)=(i∑​wi​∣xi​∣p)1/p.

reweight rescales each coordinate of xxx by the corresponding weight raised to the power 1/p1/p1/p:

reweight⁡(p,w,x)i=wi1/p xi.\operatorname{reweight}(p,w,x)_i = w_i^{1/p}\,x_i.reweight(p,w,x)i​=wi1/p​xi​.

By a theorem in the same source module, ∥reweight⁡(p,w,x)∥p=weightedNorm⁡(p,x,w)\|\operatorname{reweight}(p,w,x)\|_p = \operatorname{weightedNorm}(p,x,w)∥reweight(p,w,x)∥p​=weightedNorm(p,x,w) for p>0p>0p>0 whenever every wi≥0w_i\ge 0wi​≥0, where ∥⋅∥p\|\cdot\|_p∥⋅∥p​ is the finite coordinate power functional (DiagonalConstruction.lpNorm); and weightedNorm⁡(p,x,1)=∥x∥p\operatorname{weightedNorm}(p,x,\mathbf{1}) = \|x\|_pweightedNorm(p,x,1)=∥x∥p​ for the all-ones weight. A further theorem shows that, for fixed xxx and p>1p>1p>1, w↦weightedNorm⁡(p,x,w)w\mapsto\operatorname{weightedNorm}(p,x,w)w↦weightedNorm(p,x,w) is concave on the nonnegative weights.

Definition code
import Mathlib.Analysis.Convex.SpecificFunctions.Pow
import Mathlib.Analysis.InnerProductSpace.Basic
import Mathlib.Analysis.InnerProductSpace.Dual
import Mathlib.Analysis.Normed.Lp.PiLp
import Mathlib.Analysis.SpecialFunctions.Pow.Continuity

/-
Copyright (c) 2026 Ezzeri Esa. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Ezzeri Esa
-/

/-! # Concavity under common coordinate reweighting -/

namespace HlawkaSchatten.DiagonalConstruction

variable {ι : Type*} [Fintype ι]

noncomputable def weightedNorm (p : ℝ) (x w : ι → ℝ) : ℝ :=
  (∑ i, w i * |x i| ^ p) ^ (1 / p)

noncomputable def reweight (p : ℝ) (w x : ι → ℝ) : ι → ℝ :=
  fun i ↦ w i ^ (1 / p) * x i













end HlawkaSchatten.DiagonalConstruction
Source
https://github.com/savarin/hlawka-schatten/blob/79aa498bfcf7b22bd91d771fb32ec278e2d4704b/HlawkaSchatten/DiagonalConstruction/WeightedCoordinates.lean#L16-L20
Human review
  • Endorsed by Shuze Chen · Sep 29, 2026

    Confirmed by the moderator at approval.

  • Endorsed by savarin · Sep 29, 2026

    Confirmed by the mission captain (proposal self-audit).

  • Endorsed by marwahaha · Sep 30, 2026

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