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D.4.8.8 flatteningStrat
Procedure from library homolog.lib (see homolog_lib).
- Usage:
- flatteningStrat(M); M module
- Return:
- list of ideals.
The list entries L[1],...,L[r] describe the flattening stratification
of M'=coker(M): setting L[0]=0, L[r+1]=1, the flattening
stratification is given by the open sets Spec(A/V(L[i-1])) \ V(L[i]),
i=1,...,r+1 (A = basering).
- Note:
- for more information see the book 'A Singular Introduction to
Commutative Algebra' (by Greuel/Pfister, Springer 2002).
Example:
| | LIB "homolog.lib";
ring A = 0,x(0..4),dp;
// presentation matrix:
matrix M[2][4] = x(0),x(1),x(2),x(3),x(1),x(2),x(3),x(4);
list L = flatteningStrat(M);
L;
==> [1]:
==> _[1]=x(3)^2-x(2)*x(4)
==> _[2]=x(2)*x(3)-x(1)*x(4)
==> _[3]=x(1)*x(3)-x(0)*x(4)
==> _[4]=x(2)^2-x(0)*x(4)
==> _[5]=x(1)*x(2)-x(0)*x(3)
==> _[6]=x(1)^2-x(0)*x(2)
==> [2]:
==> _[1]=x(4)
==> _[2]=x(3)
==> _[3]=x(2)
==> _[4]=x(1)
==> _[5]=x(0)
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