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D.6.9.12 delta

Procedure from library hnoether.lib (see hnoether_lib).

Usage:
delta(INPUT); INPUT a polynomial defining an isolated plane curve singularity at 0, or the Hamburger-Noether expansion thereof, i.e. the output of develop(f), or the output of hnexpansion(f), or the list of HN data computed by hnexpansion(f).

Return:
int, the delta invariant of the singularity at 0, that is, the vector space dimension of R~/R, (R~ the normalization of the local ring of the singularity).

Note:
In case the Hamburger-Noether expansion of the curve f is needed for other purposes as well it is better to calculate this first with the aid of hnexpansion and use it as input instead of the polynomial itself.

Example:
 
See also: deltaLoc; invariants.


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