Homaloidal nets and ideals of fat points I

Abstract

One considers plane Cremona maps with proper base points and the {\em base ideal} generated by the linear system of forms defining the map. The object of this work is the interweave between the algebraic properties of the base ideal and those of the ideal of these points fattened by the virtual multiplicities arising from the linear system. One reveals conditions which naturally regulate this association, with particular emphasis on the homological side. While most classical numerical inequalities concern the three highest virtual multiplicities, here one emphasizes also the role of one single highest multiplicity. In this vein one describes classes of Cremona maps for large and small value of the highest virtual multiplicity. One also deals with the delicate property as to when the base ideal is non-saturated and the structure of its saturation.

arXiv comment29 pages, minor corrections and some update references

References in corpus (7)

• Homaloidal hypersurfaces and hypersurfaces with vanishing Hessian
• A characteristic free criterion of birationality
• Free Resolutions of Fat Point Ideals on $P^2$
• Resolutions of ideals of six fat points in P^2
• Cremona maps of de Jonquières type
• A vanishing theorem and symbolic powers of planar point ideals
• On degenerations of plane Cremona transformations

Cited by in corpus (1)

• Bounds on the degrees of birational maps with arithmetically Cohen-Macaulay graphs