Singular

D.15.9.1 curveDeltaInv

Usage:

curveDeltaInv(I); I ideal

Assume:

I is a radical ideal, dim(R/I) = 1

Return:

the delta invariant of R/I

Note:

- output -1 means: delta invariant is infinite
- the optional parameter can be used if the normalization has already been computed. If a list L contains the output of the procedure normal (with options prim, wd and usering if the ring has a mixed ordering), apply curveDeltaInv(I,L)

LIB "curveInv.lib";
ring R = 0,(x,y,z),ds;
////////////////////////////
// Finite delta invariant //
////////////////////////////
ideal I = x2y-y2z,x2-y2+z2;
curveDeltaInv(radical(I));
==> 9
//////////////////////////////
// Infinite delta invariant //
//////////////////////////////
ideal J = xyz;
curveDeltaInv(radical(J));
==> -1