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GroebnerStrata :: findWeightVector

findWeightVector -- returns a weight vector

Synopsis

Description

In the first entry, this command returns a weight vector associated to a monomial order that places the generators of a monomial ideal $M$ ahead of standard monomials of the same degree. The second entry is a list of values for the weight vector dotted with the difference of the exponent of each standard monomial for each generator and the corresponding generator.

i1 : R = ZZ/32003[a,b,c, d];
i2 : M = ideal (a^2, a*b, b^2);

o2 : Ideal of R
i3 : L = smallerMonomials M;
i4 : findWeightVector(M,L)

o4 = ({2, 2, 1, 1}, {1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1,
     ------------------------------------------------------------------------
     2, 2})

o4 : Sequence

Note that the first generator listed for $M$ is $a^2$, and the first corresponding standard monomial is $a*c$. The difference of these two monomials exponent vectors is $(1,0,-1,0)$. This vector dotted with the weight vector $(2,2,1,1)$ gives the value $1$, which is the first value in the second list.

Note that the desired term ordering, and hence weight vector, may not exist. In this case, null is returned.

i5 : M = ideal"ab"

o5 = ideal(a*b)

o5 : Ideal of R
i6 : L1 = standardMonomials M

        2   2             2                  2
o6 = {{a , b , a*c, b*c, c , a*d, b*d, c*d, d }}

o6 : List
i7 : findWeightVector(M,L1)

This command is used in the groebnerFamily routine.

See also

Ways to use findWeightVector :

For the programmer

The object findWeightVector is a method function.