next | previous | forward | backward | up | top | index | toc | Macaulay2 web site
Macaulay2Doc :: annihilator

annihilator -- the annihilator ideal

Synopsis

Description

You may use ann as a synonym for annihilator.

As an example, we compute the annihilator of the canonical module of the rational quartic curve.

i1 : R = QQ[a..d];
i2 : J = monomialCurveIdeal(R,{1,3,4})

                        3      2     2    2    3    2
o2 = ideal (b*c - a*d, c  - b*d , a*c  - b d, b  - a c)

o2 : Ideal of R
i3 : M = Ext^2(R^1/J, R)

o3 = cokernel {-3} | c  a  0 b 0 |
              {-3} | -d -b c 0 a |
              {-3} | 0  0  d c b |

                            3
o3 : R-module, quotient of R
i4 : annihilator M

                        3      2     2    2    3    2
o4 = ideal (b*c - a*d, c  - b*d , a*c  - b d, b  - a c)

o4 : Ideal of R
For another example, we compute the annihilator of an element in a quotient ring
i5 : A = R/(a*b,a*c,a*d)

o5 = A

o5 : QuotientRing
i6 : ann a

o6 = ideal (d, c, b)

o6 : Ideal of A
Macaulay2 uses two algorithms to compute annihilators. The default version is to compute the annihilator of each generator of the module M and to intersect these two by two. Each annihilator is done using a submodule quotient. The other algorithm computes the annihilator in one large computation and is used if Strategy => Quotient is specified.
i7 : annihilator(M, Strategy=>Quotient)

                        3      2     2    2    3    2
o7 = ideal (b*c - a*d, c  - b*d , a*c  - b d, b  - a c)

o7 : Ideal of R

See also

Ways to use annihilator :