The resultant formula for parametrized surfaces with non-local-complete-intersection base points

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Let I⊂C[s,t,u]I \subset \mathbb{C}[s,t,u] be generated by x,y,z,wx,y,z,w of degree nn, with V(I)V(I) finite. Assume that II is saturated and has the free resolution given by the complex referenced in the source. Let V1(A)V_1(A) and V2(A)V_2(A) denote the subschemes of P2\mathbb{P}^2 defined by the 1×11\times 1 and 2×22\times 2 minors of AA, respectively. Let P(X,Y,Z,W)=0P(X,Y,Z,W)=0 be the implicit equation of the parametrized surface, let hh be the degree of the parametrization, and for each p∈V2(A)p\in V_2(A) let ℓp=0\ell_p=0 be the equation of the plane HpH_p associated with pp. For the local ideal at pp, write epe_p for its multiplicity and dpd_p for its degree.

The resultant formula. If V1(A)=∅V_1(A)=\emptyset and V2(A)≠∅V_2(A)\ne\emptyset, then, up to a nonzero constant,

Res⁡μ1,μ2,μ3(p,q,r)=P(X,Y,Z,W)h∏p∈V2(A)ℓpep−dp.\operatorname{Res}_{\mu_1,\mu_2,\mu_3}({\bf p},{\bf q},{\bf r})=P(X,Y,Z,W)^h\prod_{p\in V_2(A)}\ell_p^{e_p-d_p}.

This conjectural formula describes the extraneous factors of the resultant arising from the points of V2(A)V_2(A), while the factor PhP^h records the implicit surface with parametrization degree hh. The source does not provide evidence of a resolution, so the conjecture is treated as open.

References

Primary source

Laurent Buse, David Cox and Carlos D'Andrea, “Implicitization of surfaces in P^3 in the presence of base points”, arXiv:math/0205251 (2003).

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