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Remove another unnecessary usage of band() #148

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Merged
dlfivefifty merged 2 commits into from
Nov 27, 2025
Merged

Remove another unnecessary usage of band() #148

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47efcea
Remove band
DanielVandH Nov 1, 2025
382aa56
Use dispatch to get around issue
DanielVandH Nov 27, 2025
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7 changes: 5 additions & 2 deletions src/SemiclassicalOrthogonalPolynomials.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -440,6 +440,9 @@ function copy(L::Ldiv{SemiclassicalJacobiLayout,SemiclassicalJacobiLayout})
(inv(M_Q) * L') * M_P
end

_get_bands(R) = (R[band(0)], R[band(-1)])
_get_bands(R::Bidiagonal) = (R.dv, R.ev)

function \(A::SemiclassicalJacobi, B::SemiclassicalJacobi{T}) where {T}
if A.b == -1 && B.b ≠ -1
return UpperTriangular(ApplyArray(inv, B \ A))
Expand All @@ -448,8 +451,8 @@ function \(A::SemiclassicalJacobi, B::SemiclassicalJacobi{T}) where {T}
Bᵗᵃ⁰ᶜ = SemiclassicalJacobi(B.t, B.a, zero(B.b), B.c, A)
Bᵗᵃ¹ᶜ = SemiclassicalJacobi(B.t, B.a, one(B.a), B.c, A)
Rᵦₐ₁ᵪᵗᵃ⁰ᶜ = Weighted(Bᵗᵃ⁰ᶜ) \ Weighted(Bᵗᵃ¹ᶜ)
b1 = Rᵦₐ₁ᵪᵗᵃ⁰ᶜ[band(0)]
b0 = Vcat(one(T), Rᵦₐ₁ᵪᵗᵃ⁰ᶜ[band(-1)])
b1, _b0 = _get_bands(Rᵦₐ₁ᵪᵗᵃ⁰ᶜ)
b0 = Vcat(one(T), _b0)
Rᵦₐ₋₁ᵪᵗᵃ⁰ᶜ = Bidiagonal(b0, b1, :U)
# Then convert Bᵗᵃ⁰ᶜ into A and complete
Rₐ₀ᵪᴬ = UpperTriangular(A \ Bᵗᵃ⁰ᶜ)
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