# Difference between revisions of "ApCoCoA-1:NC.GB"

Line 2: | Line 2: | ||

<title>NC.GB</title> | <title>NC.GB</title> | ||

<short_description> | <short_description> | ||

− | + | (Partial) Groebner basis of a finitely generated two-sided ideal over a free associative <tt>K</tt>-algebra. | |

</short_description> | </short_description> | ||

<syntax> | <syntax> | ||

− | NC.GB( | + | NC.GB(G:LIST):LIST |

− | NC.GB( | + | NC.GB(G:LIST, DegreeBound:INT, LoopBound:INT, Flag:INT):LIST |

</syntax> | </syntax> | ||

<description> | <description> | ||

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

<par/> | <par/> | ||

− | + | Please set ring environment coefficient field <tt>K</tt>, alphabet (or indeterminates) <tt>X</tt> and ordering through the functions <ref>NC.SetFp</ref>(Prime), <ref>NC.SetX</ref>(X) and <ref>NC.SetOrdering</ref>(Ordering), respectively, before calling the function. Default coefficient field is <tt>Q</tt>. Default ordering is length-lexicographic ordering (<quotes>LLEX</quotes>). For more information, please check the relevant functions. | |

<itemize> | <itemize> | ||

− | <item>@param <em> | + | <item>@param <em>G</em>: a LIST of non-zero polynomials generating a two-sided ideal. Each polynomial is represented as a LIST of LISTs, which are pairs of form [C, W] where C is a coefficient and W is a word (or term). Each term is represented as a STRING. For example, <tt>xy^2x</tt> is represented as <quotes>xyyx</quotes>, unit is represented as an empty string <quotes></quotes>. Then, polynomial <tt>F=xy-y+1</tt> is represented as F:=[[1,<quotes>xy</quotes>], [-1, <quotes>y</quotes>], [1,<quotes></quotes>]]. <tt>0</tt> polynomial is represented as an empty LIST [].</item> |

− | < | ||

</itemize> | </itemize> | ||

− | About the optional parameters: For most cases we do not know whether there exists a finite Groebner basis. Instead of forcing computer yelling and informing nothing valuable, the function has 3 optional parameters to control the computation. Note that at the moment all of the following 3 additional optional parameters must be used at the same time. | + | About the optional parameters: For most cases we do not know whether there exists a finite Groebner basis. Instead of forcing computer yelling and informing nothing valuable, the function has 3 optional parameters to control the computation. Note that at the moment <em>all</em> of the following 3 additional optional parameters must be used at the same time. |

<itemize> | <itemize> | ||

− | <item>@param <em>DegreeBound:</em> | + | <item>@param <em>DegreeBound:</em> a positive integer which gives a degree bound during Groebner basis computation. When the degree of normal remainder of some <tt>S-element</tt> reaches DegreeBound, the function stops the loop and returns a partial Groebner basis.</item> |

− | <item>@param <em>LoopBound:</em> | + | <item>@param <em>LoopBound:</em> a positive integer which gives a bound for the main loop of Groebner basis computation. When it runs through the main loop LoopBound times, the function stops the loop and returns a partial Groebner basis.</item> |

− | <item>@param <em>Flag:</em> | + | <item>@param <em>Flag:</em> a non-negative integer which is a multi-switch for the output of ApCoCoAServer. If Flag=0, the server prints nothing on the screen. If Flag=1, the server prints basic information about computing procedure, such as number of S-elements has been checked and to be checked. If Flag=2, the server additionally prints current partial Groebner basis before each loop as well as the information when Flag=1. Note that the initial idea of Flag is to use it as a tool for debugging and tracing the computing process.</item> |

+ | <item>@return: a LIST of polynomials, which is a Groebner basis if (1)finite Groebner basis exists and (2)the computation doesn't stop due to reach DegreeBound or LoopBound, and is a partial Groebner basis otherwise.</item> | ||

</itemize> | </itemize> | ||

<example> | <example> |

## Revision as of 19:59, 11 December 2010

## NC.GB

(Partial) Groebner basis of a finitely generated two-sided ideal over a free associative `K`-algebra.

### Syntax

NC.GB(G:LIST):LIST NC.GB(G:LIST, DegreeBound:INT, LoopBound:INT, Flag:INT):LIST

### Description

*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 ring environment coefficient field `K`, alphabet (or indeterminates) `X` and ordering through the functions NC.SetFp(Prime), NC.SetX(X) and NC.SetOrdering(Ordering), respectively, before calling the function. Default coefficient field is `Q`. Default ordering is length-lexicographic ordering ("LLEX"). For more information, please check the relevant functions.

@param

*G*: a LIST of non-zero polynomials generating a two-sided ideal. Each polynomial is represented as a LIST of LISTs, which are pairs of form [C, W] where C is a coefficient and W is a word (or term). Each term is represented as a STRING. For example,`xy^2x`is represented as "xyyx", unit is represented as an empty string "". Then, polynomial`F=xy-y+1`is represented as F:=[[1,"xy"], [-1, "y"], [1,""]].`0`polynomial is represented as an empty LIST [].

About the optional parameters: For most cases we do not know whether there exists a finite Groebner basis. Instead of forcing computer yelling and informing nothing valuable, the function has 3 optional parameters to control the computation. Note that at the moment *all* of the following 3 additional optional parameters must be used at the same time.

@param

*DegreeBound:*a positive integer which gives a degree bound during Groebner basis computation. When the degree of normal remainder of some`S-element`reaches DegreeBound, the function stops the loop and returns a partial Groebner basis.@param

*LoopBound:*a positive integer which gives a bound for the main loop of Groebner basis computation. When it runs through the main loop LoopBound times, the function stops the loop and returns a partial Groebner basis.@param

*Flag:*a non-negative integer which is a multi-switch for the output of ApCoCoAServer. If Flag=0, the server prints nothing on the screen. If Flag=1, the server prints basic information about computing procedure, such as number of S-elements has been checked and to be checked. If Flag=2, the server additionally prints current partial Groebner basis before each loop as well as the information when Flag=1. Note that the initial idea of Flag is to use it as a tool for debugging and tracing the computing process.@return: a LIST of polynomials, which is a Groebner basis if (1)finite Groebner basis exists and (2)the computation doesn't stop due to reach DegreeBound or LoopBound, and is a partial Groebner basis otherwise.

#### Example

NC.SetX(<quotes>xyzt</quotes>); F1 := [[1,<quotes>xx</quotes>], [-1,<quotes>yx</quotes>]]; F2 := [[1,<quotes>xy</quotes>], [-1,<quotes>ty</quotes>]]; F3 := [[1,<quotes>xt</quotes>], [-1, <quotes>tx</quotes>]]; F4 := [[1,<quotes>yt</quotes>], [-1, <quotes>ty</quotes>]]; Generators := [F1, F2,F3,F4]; NC.GB(Generators); -- over Q (default field), LLEX ordering (default ordering) [[[1, <quotes>yt</quotes>], [-1, <quotes>ty</quotes>]], [[1, <quotes>xt</quotes>], [-1, <quotes>tx</quotes>]], [[1, <quotes>xy</quotes>], [-1, <quotes>ty</quotes>]], [[1, <quotes>xx</quotes>], [-1, <quotes>yx</quotes>]], [[1, <quotes>tyy</quotes>], [-1, <quotes>tty</quotes>]], [[1, <quotes>yyx</quotes>], [-1, <quotes>tyx</quotes>]], [[1, <quotes>ttyy</quotes>], [-1, <quotes>ttty</quotes>]], [[1, <quotes>tyyx</quotes>], [-1, <quotes>ttyx</quotes>]]] ------------------------------- NC.SetFp(); -- set default Fp=F2 NC.GB(Generators); -- over F2, LLEX ordering [[[1, <quotes>yt</quotes>], [1, <quotes>ty</quotes>]], [[1, <quotes>xt</quotes>], [1, <quotes>tx</quotes>]], [[1, <quotes>xy</quotes>], [1, <quotes>ty</quotes>]], [[1, <quotes>xx</quotes>], [1, <quotes>yx</quotes>]], [[1, <quotes>tyy</quotes>], [1, <quotes>tty</quotes>]], [[1, <quotes>yyx</quotes>], [1, <quotes>tyx</quotes>]], [[1, <quotes>ttyy</quotes>], [1, <quotes>ttty</quotes>]], [[1, <quotes>tyyx</quotes>], [1, <quotes>ttyx</quotes>]]] ------------------------------- NC.SetFp(3); NC.GB(Generators); -- over F3, LLEX ordering [[[1, <quotes>yt</quotes>], [2, <quotes>ty</quotes>]], [[1, <quotes>xt</quotes>], [2, <quotes>tx</quotes>]], [[1, <quotes>xy</quotes>], [2, <quotes>ty</quotes>]], [[1, <quotes>xx</quotes>], [2, <quotes>yx</quotes>]], [[1, <quotes>tyy</quotes>], [2, <quotes>tty</quotes>]], [[1, <quotes>yyx</quotes>], [2, <quotes>tyx</quotes>]], [[1, <quotes>ttyy</quotes>], [2, <quotes>ttty</quotes>]], [[1, <quotes>tyyx</quotes>], [2, <quotes>ttyx</quotes>]]] -------------------------------

### See also