ApCoCoA-1:NC.Intersection: Difference between revisions

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<title>NC.Intersection</title>
<title>NC.Intersection</title>
<short_description>
<short_description>
Enumerate a (partial) Groebner basis of the intersection of two finitely generated two-sided ideals in a free monoid ring.
Intersection of two finitely generated two-sided ideals in a free monoid ring.
</short_description>
</short_description>
<syntax>
NC.Intersection(G1:LIST, G2:LIST):LIST
NC.Intersection(G1:LIST, G2:LIST, DegreeBound:INT, LoopBound:INT, Flag:INT):LIST
</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>Propostion (Intersection of Two Ideals):</em> Let <tt>G_I</tt> and <tt>G_J</tt> be two sets of non-zero polynomials in the free nomoid ring <tt>K&lt;x_1,...,x_n&gt;</tt>, and let <tt>I</tt> and <tt>J</tt> be two ideals generated by <tt>G_I</tt> and <tt>G_J</tt>, respectively. We choose a new indeterminate <tt>y</tt>, and form the free monoid ring <tt>K&lt;y,x_1,...,x_n&gt;</tt>. Furthermore, let <tt>N</tt> be the ideal generated by the union of <tt>{yf: f in G_I}</tt> and <tt>{(1-y)g: g in G_J}</tt>, and let <tt>C</tt> be the ideal generated by the set <tt>{yx_1-x_1y,...,yx_n-x_ny}</tt> of commutators. Then we have the intersection of <tt>I</tt> and <tt>J</tt> is equal to the intersection of <tt>N+C</tt> and <tt>K&lt;x_1,...,x_n&gt;</tt>.
<par/>
Please set ring environment <em>coefficient field</em> <tt>K</tt>, <em>alphabet</em> (or set of indeterminates) <tt>X</tt> and <em>ordering</em> via the functions <ref>NC.SetFp</ref>, <ref>NC.SetX</ref> and <ref>NC.SetOrdering</ref>, respectively, before calling the function. The default coefficient field is <tt>Q</tt>. The default ordering is length-lexicographic ordering (<quotes>LLEX</quotes>). For more information, please check the relevant functions.
<itemize>
<item>@param <em>G1, G2:</em> two LISTs of non-zero polynomials which generate two two-sided ideals in <tt>K&lt;X&gt;</tt>. Each polynomial is represented as a LIST of monomials, which are pairs of the form [C, W] where W is a word in <tt>&lt;X&gt;</tt> and C is the coefficient of W. For example, the polynomial <tt>F=xy-y+1</tt> is represented as F:=[[1,<quotes>xy</quotes>], [-1, <quotes>y</quotes>], [1,<quotes></quotes>]].</item>
</itemize>
Since this function is based on Groebner basis computations, we refer users to <ref>NC.GB</ref> or <ref>NC.ReducedGB</ref> for information about the following three optional parameters:
<itemize>
<item>@param <em>DegreeBound</em></item>
<item>@param <em>LoopBound</em></item>
<item>@param <em>Flag</em></item>
<item>@return: a LIST of polynomials, which is a Groebner basis of the intersection of the two-sided ideals <tt>(G1)</tt> and <tt>(G2)</tt> if a finite Groebner basis exists, and is a partial Groebner basis otherwise.</item>
</itemize>
<example>
<example>
NC.SetFp(); -- set default Fp=F2
-- Let I be the ideal generated by G_I={xy+z,yz+x}, and J be the ideal generated by G_J={yz+x, zx+y}.
NC.SetX(<quotes>xyz</quotes>);  
-- We compute the intersection of I and J as follows.
F1 := [[1,<quotes>xy</quotes>], [1,<quotes>z</quotes>]];  
NC.SetX("txyz"); -- Let t be an new indeterminate
F2 := [[1,<quotes>yz</quotes>], [1, <quotes>x</quotes>]];  
NC.SetOrdering("ELIM"); -- Choose an elimination word ordering for t
F3 := [[1,<quotes>zx</quotes>], [1,<quotes>y</quotes>]];
F1 := [[1,"xy"], [1,"z"]]; -- xy+z
G1 := [F1, F2]; -- ideal generated by {xy+z, yz+x}
F2 := [[1,"yz"], [1,"x"]]; -- yz+x
G2 := [F2, F3]; -- ideal generated by {yz+x, zx+y}
G1 := [[1,"yz"], [1,"x"]]; -- yz+x
NC.Intersection(G1, G2, 20, 25, 1);
G2 := [[1,"zx"], [1,"y"]]; -- zx+y
[[[1, <quotes>yzyz</quotes>], [1, <quotes>zyzy</quotes>]], [[1, <quotes>zzyzyy</quotes>], [1, <quotes>yyzy</quotes>], [1, <quotes>zyzz</quotes>], [1, <quotes>yz</quotes>]],
N:=[NC.Multiply([[1,"t"]],F1), NC.Multiply([[1,"t"]],F2)]; -- t*F1, t*F2
[[1, <quotes>yzzyzy</quotes>], [1, <quotes>yzyy</quotes>], [1, <quotes>zzyz</quotes>], [1, <quotes>zy</quotes>]], [[1, <quotes>x</quotes>], [1, <quotes>yz</quotes>]]]
N:=Concat(N,[NC.Multiply([[1,""],[-1,"t"]],G1), NC.Multiply([[1,""],[-1,"t"]],G2)]); -- (1-t)*G1, (1-t)*G2
C:=[[[1,"tx"],[-1,"xt"]],[[1,"ty"],[-1,"yt"]],[[1,"tz"],[-1,"zt"]]]; -- set of commutators
G:=Concat(N,C);
Gb:=NC.GB(G,20,50,1);
 
-- Done.
-------------------------------
-------------------------------
Note the following information printed by the server shows it is a partial Groebner basis.  
 
===== 25th Loop =====
 
Number of elements in (partial) Groebner basis G: 22 -- partial Groebner basis before being interreduced
The following information printed by the ApCoCoAServer shows that Gb it is a partial Groebner basis.  
Number of S-elements: 25/86 -- 25 S-elements have been check, and 61 (=86-25) unchecked S-elements
the number of unselected generators: 0
the number of unselected ObstructionMs: 70
the procedure is interrupted by loop bound!
the total number of ObstructionMs: 298
the number of selected ObstructionMs: 43
the number of ObstructionMs detected by Rule 1: 145
the number of ObstructionMs detected by Rule 2: 0
the number of ObstructionMs detected by Rule 3: 40
the number of redundant generators: 6
It is a partial Groebner basis.
</example>
</example>
</description>
</description>
<seealso>
<seealso>
<see>NC.Add</see>
<see>NC.FindPolys</see>
<see>NC.Deg</see>
<see>NC.FindPolynomials</see>
<see>NC.GB</see>
<see>NC.GB</see>
<see>NC.HF</see>
<see>NC.Mul</see>
<see>NC.Interreduction</see>
<see>NC.Intersection</see>
<see>NC.IsFinite</see>
<see>NC.IsGB</see>
<see>NC.IsHomog</see>
<see>NC.KernelOfHomomorphism</see>
<see>NC.LC</see>
<see>NC.LT</see>
<see>NC.LTIdeal</see>
<see>NC.MB</see>
<see>NC.MinimalPolynomial</see>
<see>NC.Multiply</see>
<see>NC.NR</see>
<see>NC.ReducedGB</see>
<see>NC.SetFp</see>
<see>NC.SetOrdering</see>
<see>NC.SetOrdering</see>
<see>NC.SetRelations</see>
<see>NC.SetRules</see>
<see>NC.SetX</see>
<see>NC.Subtract</see>
<see>NC.TruncatedGB</see>
<see>NC.UnsetFp</see>
<see>NC.UnsetOrdering</see>
<see>NC.UnsetRelations</see>
<see>NC.UnsetRules</see>
<see>NC.UnsetX</see>
<see>Introduction to CoCoAServer</see>
</seealso>
</seealso>
<types>
<types>
Line 80: Line 50:
<type>non_commutative</type>
<type>non_commutative</type>
</types>
</types>
<key>gbmr.Intersection</key>
<key>ncpoly.Intersection</key>
<key>NC.Intersection</key>
<key>NC.Intersection</key>
<key>Intersection</key>
<key>Intersection</key>
<wiki-category>Package_gbmr</wiki-category>
<wiki-category>Package_ncpoly</wiki-category>
</command>
</command>

Revision as of 14:45, 9 May 2013

NC.Intersection

Intersection of two finitely generated two-sided ideals in a free monoid ring.

Description

Propostion (Intersection of Two Ideals): Let G_I and G_J be two sets of non-zero polynomials in the free nomoid ring K<x_1,...,x_n>, and let I and J be two ideals generated by G_I and G_J, respectively. We choose a new indeterminate y, and form the free monoid ring K<y,x_1,...,x_n>. Furthermore, let N be the ideal generated by the union of {yf: f in G_I} and {(1-y)g: g in G_J}, and let C be the ideal generated by the set {yx_1-x_1y,...,yx_n-x_ny} of commutators. Then we have the intersection of I and J is equal to the intersection of N+C and K<x_1,...,x_n>.

Example

-- Let I be the ideal generated by G_I={xy+z,yz+x}, and J be the ideal generated by G_J={yz+x, zx+y}.
-- We compute the intersection of I and J as follows.
NC.SetX("txyz"); -- Let t be an new indeterminate
NC.SetOrdering("ELIM"); -- Choose an elimination word ordering for t
F1 := [[1,"xy"], [1,"z"]]; -- xy+z
F2 := [[1,"yz"], [1,"x"]]; -- yz+x
G1 := [[1,"yz"], [1,"x"]]; -- yz+x
G2 := [[1,"zx"], [1,"y"]]; -- zx+y
N:=[NC.Multiply([[1,"t"]],F1), NC.Multiply([[1,"t"]],F2)]; -- t*F1, t*F2
N:=Concat(N,[NC.Multiply([[1,""],[-1,"t"]],G1), NC.Multiply([[1,""],[-1,"t"]],G2)]); -- (1-t)*G1, (1-t)*G2
C:=[[[1,"tx"],[-1,"xt"]],[[1,"ty"],[-1,"yt"]],[[1,"tz"],[-1,"zt"]]]; -- set of commutators
G:=Concat(N,C); 
Gb:=NC.GB(G,20,50,1);

-- Done.
-------------------------------


The following information printed by the ApCoCoAServer shows that Gb it is a partial Groebner basis. 
the number of unselected generators:	0
the number of unselected ObstructionMs:	70
the procedure is interrupted by loop bound!
the total number of ObstructionMs:	298
the number of selected ObstructionMs:	43
the number of ObstructionMs detected by Rule 1:	145
the number of ObstructionMs detected by Rule 2:	0
the number of ObstructionMs detected by Rule 3:	40
the number of redundant generators:	6
It is a partial Groebner basis.

See also

NC.FindPolys

NC.GB

NC.Mul

NC.SetOrdering




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