Labelled Runge-Kutta B-series #
This file defines labelled elementary weights for additive, or coloured, Runge-Kutta tableaus. The coefficients of a node are selected by its label.
Main definitions #
LabelledRungeKutta- a labelled tableau with oneAandbfamily per labelLabelledRungeKutta.stageWeight- planar labelled stage weightsLabelledRungeKutta.treeWeight- non-planar labelled tree weightsLabelledRungeKutta.series- the induced labelled B-series
Pull a labelled Runge-Kutta tableau back along a relabelling map.
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Restrict a labelled Runge-Kutta tableau to one constant label.
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Label-dependent row sum cᵢᵃ = ∑ⱼ Aᵃᵢⱼ.
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Recursive stage weight of a planar labelled tree.
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- rk.stageWeight (HopfAlgebras.PLTree.node a ts) x✝ = rk.stageWeightList ts x✝
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Product of child contributions in the recursive labelled stage weight.
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- rk.stageWeightList [] x✝ = 1
- rk.stageWeightList (t :: ts) x✝ = (∑ j : ι, rk.A t.rootLabel x✝ j * rk.stageWeight t j) * rk.stageWeightList ts x✝
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Stage weights are invariant under the labelled non-planar tree relation.
Stage-weight products are invariant under elementwise equivalent child lists.
Elementary weight of a planar labelled rooted tree.
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- rk.weight (HopfAlgebras.PLTree.node a ts) = ∑ i : ι, rk.b a i * rk.stageWeightList ts i
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Elementary weights are invariant under the labelled non-planar tree relation.
Multiplicative extension of labelled elementary weights to planar forests.
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- rk.weightList ts = (List.map rk.weight ts).prod
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Recursive stage weight of a non-planar labelled rooted tree.
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- rk.treeStageWeight τ i = Quotient.lift (fun (t : HopfAlgebras.PLTree α) => rk.stageWeight t i) ⋯ τ
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Product of child stage contributions over a non-planar labelled rooted forest.
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- rk.forestStageWeight φ i = (Multiset.map (fun (τ : HopfAlgebras.LRootedTree α) => ∑ j : ι, rk.A τ.rootLabel i j * rk.treeStageWeight τ j) φ).prod
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Elementary weight of a non-planar labelled rooted tree.
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- rk.treeWeight τ = Quotient.lift rk.weight ⋯ τ
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Multiplicative extension of labelled elementary weights to non-planar labelled forests.
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- rk.forestWeight φ = (Multiset.map rk.treeWeight φ).prod
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The labelled B-series induced by a labelled Runge-Kutta tableau.
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- rk.series BSeries.LTreeIndex.empty = 1
- rk.series (BSeries.LTreeIndex.tree τ) = rk.treeWeight τ
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Two labelled Runge-Kutta tableaux have matching labelled B-series coefficients
through order n.
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- rk.AgreeUpToOrder rk' n = rk.series.AgreeUpToOrder rk'.series n
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Promote an ordinary Runge-Kutta tableau to a label-independent labelled tableau.
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A labelled Runge-Kutta tableau has order n when its labelled B-series
agrees with the exact labelled B-series through order n.