# ApCoCoA-1:NC.RedGB

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## NC.RedGB

Enumerate reduced (partial) Groebner bases of finitely generated two-sided ideals in a non-commutative polynomial ring.

### Syntax

```NC.RedGB(G:LIST[, Optimize:INT, OFlag:INT, DB:INT, LB:INT]):LIST
```

### Description

Given a word ordering and a two-sided ideal I, a set of non-zero polynomials Gb is called a Groebner basis of I if the leading word set LW{Gb} generates the leading word ideal LW(I). A Groebner basis Gb of I is reduced if Gb is interreduced (see NC.Interreduction) and all polynomials in Gb are monic. Note that each ideal has a unique (not necessarily finite) reduced Groebner basis.

Please note: The function(s) explained on this page is/are using the ApCoCoAServer. You will have to start the ApCoCoAServer in order to use it/them.

Please set non-commutative polynomial ring (via the command Use) and word ordering (via the function NC.SetOrdering) before calling this function. The default word ordering is the length-lexicographic ordering ("LLEX"). For more information, please check the relevant commands and functions.

• @param G: a LIST of non-zero non-commutative polynomials that generate a two-sided ideal. Each polynomial is represented as a LIST of LISTs, and each element in every inner LIST involves only one indeterminate or none (a constant). For example, the polynomial f=2xyx^2-9yx^2x^3+5 is represented as F:=[[2x,y,x^2], [-9y,x^2,x^3], ]. The zero polynomial 0 is represented as the empty LIST [].

• @return: a LIST of interreduced non-zero non-commutative polynomials, which is a reduced Groebner basis of the two-sided ideal generated by G if (1) there exists a finite Groebner basis and (2) the enumerating procedure was not interrupted by the degree bound DB or the loop bound LB, and is a reduced partial Groebner basis otherwise.

• @param Optimize: an INT between 0 and 31. The value of Optimize indicates which criteria are used in the Buchberger procedure. For the time being, the function supports 5 criteria as follows.

``` The multiply criterion: Optimize=1;
The tail reduction criterion: Optimize=4;
The backward criterion: Optimize=8;
(Reference: M. Kreuzer and X. Xiu, Non-Commutative Gebauer-Moeller Criteria, 2013.)
```

One can choose none, one, or more than one criterion in the function. For instance, Optimize=0 means no criterion is used, Optimize=1 means applying the multiply criterion, Optimize=3 (1+2) means applying the multiply and the leading word criteria, etc. By default, Optimize=31, i.e. the function applies all criteria.

• @param OFlag: an INT that indicates which information will be output by the ApCoCoAServer during the Buchberger enumerating procedure. If OFlag=1, the server outputs basic information, such as the number of enumerating steps that has been proceeded, the number of elements in partial Groebner basis, the degree of current selected obstruction, the number of unselected obstructions, the total number of obstructions, the number of selected obstructions, and the number of unnecessary obstructions. If OFlag=2, besides the information as OFlag=1, the server also displays explicitly the elements in partial Groebner basis and the current selected S-polynonial. Otherwise, the server outputs nothing during the procedure.

• @param DB: a positive INT, which gives a degree bound of S-polynomials (or obstructions) during the Buchberger enumerating procedure. When the degree bound is reached, the procedure will be interrupted and return a partial Groebner basis.

• @param LB: a positive INT, which gives a loop bound of enumerating steps. When the LB-th enumerating step finishes, the procedure will be interrupted and return a partial Groebner basis.

#### Example

```Use ZZ/(2)[x,y,t];
NC.SetOrdering("LLEX");
F1 := [[x^2], [y,x]]; -- x^2+yx
F2 := [[x,y], [t,y]]; -- xy+ty
F3 := [[x,t], [t,x]]; -- xt+tx
F4 := [[y,t], [t,y]]; -- yt+ty
F5:=[[y,t,x],];
G := [F1, F2,F3,F4,F5];
NC.RedGB(G);

[[[x], [t]], [[t^3], ], [[y], [t]]]
-------------------------------
```