Labelled B-Series #
This file defines labelled B-series coefficient families and their multiplicative extension to the labelled rooted-forest algebra.
Main definitions #
LTreeIndex α- labelled rooted trees with an adjoined empty treeLSeries α R- coefficient families indexed by labelled rooted treesLSeries.toCharacter- multiplicative extension to labelled forest charactersLSeries.ofCharacter- recover labelled coefficients from a forest characterLSeries.characterEquiv- equivalence between unit-constant series and charactersLSeries.unit- convolution identity coefficientsLSeries.exact- exact-flow coefficients, ignoring labelsLSeries.scaledExact- exact-flow coefficients with a time/step-size parameterLSeries.AgreeUpToOrder- coefficient agreement through a labelled tree orderLSeries.HasOrder- order conditions relative to exact labelled coefficientsLSeries.comapMapLabels- pull back labelled coefficients by relabellingLSeries.comapConstLabel- restrict labelled coefficients to one constant labelLSeries.comapEraseLabels- pull back unlabelled coefficients by erasing labelsLSeries.LabelInvariant- labelled coefficients that descend to unlabelled trees
Labelled rooted trees with an adjoined empty tree.
- empty {α : Type u} : LTreeIndex α
- tree {α : Type u} : HopfAlgebras.LRootedTree α → LTreeIndex α
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The order of a labelled B-series tree index.
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Predicate for labelled B-series tree indices of a fixed order.
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Butcher's tree factorial for labelled B-series tree indices.
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Forget labels from a labelled B-series tree index.
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Relabel a labelled B-series tree index.
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Label every vertex of an unlabelled B-series tree index by the same label.
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A labelled B-series over R, represented by labelled-tree coefficients.
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- BSeries.LSeries α R = (BSeries.LTreeIndex α → R)
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The coefficient of a labelled rooted tree index in a labelled B-series.
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The coefficient of the empty labelled tree.
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The condition a(∅) = 1, used for labelled B-series considered as maps.
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- a.HasUnitConstant = (a.constantCoeff = 1)
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The condition a(∅) = 0, used for labelled B-series considered as vector fields.
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- a.HasZeroConstant = (a.constantCoeff = 0)
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Multiplicative coefficient of a labelled rooted forest induced by a series.
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- a.forestCoeff φ = (Multiset.map (fun (τ : HopfAlgebras.LRootedTree α) => a.coeff (BSeries.LTreeIndex.tree τ)) φ).prod
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The labelled forest-algebra character induced by the tree coefficients of a series.
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Recover the unit-constant labelled B-series determined by a labelled forest character.
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Unit-constant labelled B-series are equivalent to labelled forest characters.
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The labelled convolution identity coefficients.
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Exact labelled B-series coefficients, ignoring labels.
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- BSeries.LSeries.exact α R τ = (↑τ.treeFactorial)⁻¹
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Exact labelled B-series coefficients at time/step-size h, ignoring labels.
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- BSeries.LSeries.scaledExact α R h τ = h ^ τ.order * (↑τ.treeFactorial)⁻¹
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Two labelled B-series agree through order n.
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- a.AgreeUpToOrder b n = ∀ (τ : BSeries.LTreeIndex α), τ.order ≤ n → a.coeff τ = b.coeff τ
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Coefficient-level order conditions for a labelled B-series.
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- a.HasOrder n = a.AgreeUpToOrder (BSeries.LSeries.exact α R) n
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Pull a labelled B-series back along a relabelling map.
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- BSeries.LSeries.comapMapLabels f a τ = a.coeff (BSeries.LTreeIndex.mapLabels f τ)
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Restrict a labelled B-series to trees where every vertex has the same label.
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- BSeries.LSeries.comapConstLabel x a τ = a.coeff (BSeries.LTreeIndex.constLabel x τ)
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Pull an unlabelled B-series back to labelled trees by forgetting labels.
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- BSeries.LSeries.comapEraseLabels a τ = a.coeff τ.erase
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A labelled B-series whose coefficients only depend on the unlabelled tree.
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- a.LabelInvariant = ∀ (τ σ : BSeries.LTreeIndex α), τ.erase = σ.erase → a.coeff τ = a.coeff σ
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Unlabelled series are equivalent to labelled series whose coefficients ignore labels.
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Unit-constant unlabelled series are equivalent to unit-constant label-invariant series.
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Unit-constant label-invariant series are equivalent to label-invariant characters.
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