|  |  7.5.18 ncpreim_lib 
Library:
ncpreim.lib
Purpose:
    Non-commutative elimination and preimage computations
Author:
Daniel Andres, daniel.andres@math.rwth-aachen.de
Support: DFG Graduiertenkolleg 1632 `Experimentelle und konstruktive Algebra'
 
Overview:
In G-algebras, elimination of variables is more involved than in the
commutative case.
One, not every subset of variables generates an algebra, which is again a
G-algebra.
 Two, even if the subset of variables in question generates an admissible
subalgebra, there might be no admissible elimination ordering, i.e. an
elimination ordering which also satisfies the ordering condition for
G-algebras.
 
The difference between the procedure eliminateNCprovided in this
library and the procedureeliminate (plural)from the kernel is that
eliminateNC will always find an admissible elimination if such one exists.
Moreover, the use ofslimgbfor performing Groebner basis computations
is possible. 
As an application of the theory of elimination, the procedure preimageNCis provided, which computes the preimage of an ideal under a homomorphism
f: A -> B between G-algebras A and B. In contrast to the kernel procedurepreimage (plural), the assumption that A is commutative is not required. 
References:
(BGL) J.L. Bueso, J. Gomez-Torrecillas, F.J. Lobillo:
`Re-filtering and exactness of the Gelfand-Kirillov dimension',
Bull. Sci. math. 125, 8, 689-715, 2001.
(GML) J.I. Garcia Garcia, J. Garcia Miranda, F.J. Lobillo:
`Elimination orderings and localization in PBW algebras',
Linear Algebra and its Applications 430(8-9), 2133-2148, 2009.
 (Lev) V. Levandovskyy: `Intersection of ideals with non-commutative
subalgebras', ISSAC'06, 212-219, ACM, 2006.
 
 
Procedures:
See also:
 elim_lib;
 preimage (plural). 
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