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work on polynomial_composition. Close #520 #524

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work on polynomial_composition. Close #520 #524

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10 changes: 10 additions & 0 deletions src/polynomials/standard-basis/immutable-polynomial.jl
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Expand Up @@ -106,8 +106,18 @@ function polynomial_composition(p::ImmutableDensePolynomial{B,T,X,N}, q::Immutab
cs = evalpoly(q, p.coeffs)
convert(P, cs)
end
function polynomial_composition(p::AbstractUnivariatePolynomial{B,T,X}, q::ImmutableDensePolynomial{B,S,Y,0}) where {B<:StandardBasis,T,S,X,Y}
P = ImmutableDensePolynomial{B,promote_type(T,S), Y,0}
zero(P)
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A polynomial composed with zero is the polynomial's constant term, not always zero. For example, if we have f(x) = 1 and g(x) = 0, f∘g is 1, not 0.

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Apart from that, I don't think the promotion is necessary, that is, I think you could just ignore S, because the value of q is always zero, independently of S.

end

function polynomial_composition(p::AbstractUnivariatePolynomial{B,T,X}, q::ImmutableDensePolynomial{B,S,Y,1}) where {B<:StandardBasis,T,S,X,Y}
P = ImmutableDensePolynomial{B,promote_type(T,S), Y,1}
P(evalpoly(constantterm(q),p))
end

# special cases of polynomial composition

# ... TBD ...


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