Classify
Coding
Deformations
Equidim Part
Existence
Finite Groups
Flatness
Genus
Hilbert Series
Membership
Monodromy
Normalization
Primdec
Puiseux
Plane Curves
Solving
Space Curves
Spectrum
Singularities of plane curves - An Example

ring s = 0,(x,y),ds;
poly f = y2-2x28y-4x21y17+4x14y33-8x7y49+x56+20y65+4x49y16;
LIB "sing.lib";
LIB "classify.lib";
classify(f);
==> The singularity is R-equivalent to A[2260]: y2+x2261
Milnor number(f) = 2260
modality(f) = 0
ring r = 0,(x,y),dp;
poly f = fetch(s,f);
tjurina(f);
==> 2260
Hence, Tglobal(f) = Tlocal(f) (= local Milnor number for Ak-sing.). ring sh = 0,(x,y,z),dp;
poly f = fetch(s,f);
poly F = homog(f,z); // homogeneous polynomial defining C
ring r1 = 0,(y,z),dp;
map phi = sh,1,y,z;
poly g = phi(F); // F in affine chart (x=1)
tjurina(g);
==> 120

ring r2 = 0,(y,z),ds; // local ring at (1:0:0)
poly g = fetch(r1,g);
tjurina(g);
==> 120
We conclude: there is (precisely) 1 singularity of C at infinity.
(We have considered all points at infinity except (0:1:0) which is obviously not on C.) Topological type of the singularity at (1:0:0) : x9-y16 = 0.


Lille, 08-07-02 http://www.singular.uni-kl.de