Singular Manual: CSMA

| #### D.5.2.59 CSMA Procedure from library `chern.lib` (see chern_lib). Usage: CSMA(I); I an ideal Return: list of integers Purpose: computes the Chern-Schwartz-MacPherson classes of the variety defined by I Note: Example:
    LIB "chern.lib";
    // consider the projective plane with homogeneous coordinates x, y, z
    ring r = 0, (x, y, z), dp;
    // the Chern-Schwartz-MacPherson class of a smooth cubic:
    ideal I=x3+y3+z3;
    I;
    ==> I[1]=x3+y3+z3
    CSMA(I);
    ==> [1]:
    ==>    0
    ==> [2]:
    ==>    3
    ==> [3]:
    ==>    0
    // the Chern-Schwartz-MacPherson class of singular cubic
    // that is a union of 3 non-collinear lines:
    ideal J=x*y*z;
    J;
    ==> J[1]=xyz
    CSMA(J);
    ==> [1]:
    ==>    0
    ==> [2]:
    ==>    3
    ==> [3]:
    ==>    3
    // the Chern-Schwartz-MacPherson class of singular cubic
    // that is a union of 3 lines passing through one point
    ideal K=x*y*(x+y);
    K;
    ==> K[1]=x2y+xy2
    CSMA(K);
    ==> [1]:
    ==>    0
    ==> [2]:
    ==>    3
    ==> [3]:
    ==>    4

User manual for Singular version 4.4.1, 2025, generated by texi2html.