Interpolation Package that works within Symbolics/MTK

HSnowden · May 30, 2024, 2:42pm

Hello,

I have a use case that requires an interpolation to be used from within a Modeling Toolkit Model as well as Symbolics Num’s. From what I understand the only package that can do this is DataInterpolations.jl, at least my testing with Dierckx.jl said no. However, I also need this package to extrapolate and specifically extrapolate flatly at the boundary conditions. Is there a way to alter DataInterpolations.jl so that it does flat extrapolation or another package with Symbolics.jl compatability.

Thanks for any help

ChrisRackauckas · May 30, 2024, 3:03pm

We can add that interpolation to DataInterpolations.jl. It also wouldn’t be so hard to add this same extension to Dierckx.jl

github.com

SciML/DataInterpolations.jl/blob/master/ext/DataInterpolationsSymbolicsExt.jl

module DataInterpolationsSymbolicsExt

if isdefined(Base, :get_extension)
    using DataInterpolations: AbstractInterpolation
    import DataInterpolations: derivative
    using Symbolics
    using Symbolics: Num, unwrap, SymbolicUtils
else
    using ..DataInterpolations: AbstractInterpolation
    import ..DataInterpolations: derivative
    using ..Symbolics
    using ..Symbolics: Num, unwrap, SymbolicUtils
end

(interp::AbstractInterpolation)(t::Num) = SymbolicUtils.term(interp, unwrap(t))
SymbolicUtils.promote_symtype(t::AbstractInterpolation, _...) = Real
Base.nameof(interp::AbstractInterpolation) = :Interpolation

function derivative(interp::AbstractInterpolation, t::Num, order = 1)
    Symbolics.wrap(SymbolicUtils.term(derivative, interp, unwrap(t), order))

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HSnowden · May 30, 2024, 3:56pm

Either would be excellent tbh.