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MikaelSlevinsky committed Nov 21, 2024
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4 changes: 2 additions & 2 deletions examples/semiclassical.jl
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Expand Up @@ -52,7 +52,7 @@ savefig(joinpath(GENFIGS, "semiclassical.html"))
###<object type="text/html" data="../semiclassical.html" style="width:100%;height:400px;"></object>
###```

# By [Theorem 2.20](https://arxiv.org/abs/2302.08448) it turns out that the *derivatives* of these particular semi-classical Jacobi polynomials are a linear combination of at most four polynomials orthogonal with respect to $(1-x)^{\alpha+1}(1+x)^{\beta+1}(2+x)^{\gamma+1}(3+x)^{\delta+1}(5-x)^{\epsilon+1}$ on $(-1,1)$. This fact enables us to compute the banded differentiation matrix:
# By [Theorem 2.20](https://arxiv.org/abs/2302.08448) it turns out that the *derivatives* of these particular semi-classical Jacobi polynomials are a linear combination of at most four polynomials orthogonal with respect to the weight $w^{(\alpha+1,\beta+1,\gamma+1,\delta+1,\epsilon+1)}(x)$ on $(-1,1)$. This fact enables us to compute the banded differentiation matrix:
v = Fun(x->(2+x)^+1)*(3+x)^+1)*(5-x)^+1), NormalizedJacobi+1, α+1))
function threshold!(A::AbstractArray, ϵ)
for i in eachindex(A)
Expand All @@ -61,6 +61,6 @@ function threshold!(A::AbstractArray, ϵ)
A
end
P′ = plan_modifiedjac2jac(Float64, n+1, α+1, β+1, v.coefficients)
DP = UpperTriangular(diagm(1=>[sqrt(n*(n+α+β+1)) for n in 1:n])) # The classical differentiation matrix representing 𝒟 P^{(-1/2,0)}(y) = P^{(1/2,1)}(y) D_P.
DP = UpperTriangular(diagm(1=>[sqrt(n*(n+α+β+1)) for n in 1:n])) # The classical differentiation matrix representing 𝒟 P^{(α,β)}(y) = P^{(α+1,β+1)}(y) D_P.
DQ = UpperTriangular(threshold!(P′\(DP*(P*I)), 100eps())) # The semi-classical differentiation matrix representing 𝒟 Q(y) = Q̂(y) D_Q.
UpperTriangular(DQ[1:10,1:10])

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