<p>The <em>Bianchi groups</em> are the groups <span class="SimpleMath">\(G_{-d}=PSL_2({\cal O}_{-d})\)</span> where <span class="SimpleMath">\(d\)</span> is a square free positive integer and <span class="SimpleMath">\({\cal O}_{-d}\)</span> is the ring of integers of the imaginary quadratic field <span class="SimpleMath">\(\mathbb Q(\sqrt{-d})\)</span>. These groups act on <em>upper-half space</em></p>
<p>where we use the symbol <span class="SimpleMath">\(j\)</span> satisfying <span class="SimpleMath">\(j^2=-1\)</span>, <span class="SimpleMath">\(ij=-ji\)</span> and write <span class="SimpleMath">\(z+tj\)</span> instead of <span class="SimpleMath">\((z,t)\)</span>. Alternatively, the action is given by</p>
<p>We take the boundary <span class="SimpleMath">\(\partial {\frak h}^3\)</span> to be the Riemann sphere <span class="SimpleMath">\(\mathbb C \cup \infty\)</span> and let <span class="SimpleMath">\(\overline{\frak h}^3\)</span> denote the union of <span class="SimpleMath">\({\frak h}^3\)</span> and its boundary. The action of <span class="SimpleMath">\(G_{-d}\)</span> extends to the boundary. The element <span class="SimpleMath">\(\infty\)</span> and each element of the number field <span class="SimpleMath">\(\mathbb Q(\sqrt{-d})\)</span> are thought of as lying in the boundary <span class="SimpleMath">\(\partial {\frak h}^3\)</span> and are referred to as <em>cusps</em>. Let <span class="SimpleMath">\(X\)</span> denote the union of <span class="SimpleMath">\({\frak h}^3\)</span> with the set of cusps, <span class="SimpleMath">\(X={\frak h}^3 \cup \{\infty\} \cup \mathbb Q(\sqrt{-d})\)</span>. It follows from work of Bianchi and Humbert that the space <span class="SimpleMath">\(X\)</span> admits the structure of a regular CW-complex (depending on <span class="SimpleMath">\(d\)</span>) for which the action of <span class="SimpleMath">\(G_{-d}\)</span> on <span class="SimpleMath">\({\frak h}^3\)</span> extends to a cellular action on <span class="SimpleMath">\(X\)</span> which permutes cells. Moreover, <span class="SimpleMath">\(G_{-d}\)</span> acts transitively on the <span class="SimpleMath">\(3\)</span>-cells of <span class="SimpleMath">\(X\)</span> and each <span class="SimpleMath">\(3\)</span>-cell has trivial stabilizer in <span class="SimpleMath">\(G_{-d}\)</span>. Details are provided in Richard Swan's paper <a href="chapBib_mj.html#biBswanB">[Swa71b]</a>.</p>
<p>We refer to the closure in <span class="SimpleMath">\(X\)</span> of any one of these <span class="SimpleMath">\(3\)</span>-cells as a <em>fundamental domain</em> for the action <span class="SimpleMath">\(G_{-d}\)</span>. Cohomology of <span class="SimpleMath">\(G_{-d}\)</span> can be computed from a knowledge of the combinatorial structure of this fundamental domain together with a knowledge of the stabilizer groups of the cells of dimension <span class="SimpleMath">\(\le 2\)</span>.</p>
<p><a id="java.lang.StringIndexOutOfBoundsException: Index 15 out of bounds for length 0
<h4>14.2 <span class="Heading">Swan's description of a fundamental domain</span></h4>
<p>A pair <span class="SimpleMath">\((a,b)\)</span> of elements in <span class="SimpleMath">\({\cal O}_{-d}\)</span> is said to be <em>unimodular</em> if the
<p>When span =""\D=overlineF \ap B})<span> where closurehas span"impleMath>\\ D\<> four <span class=S"\2\<>- <=>(\/>ofjava.lang.StringIndexOutOfBoundsException: Range [371, 370) out of bounds for length 1069
<p>It is explained in <a href="chapBib_mj.html#biBswanB">[Swa71b]</a> that <span class="SimpleMath">\(F\cap B\)</span> is a <span class="SimpleMath">\(3\)</span>-cell in the above mentioned regular CW-complex structure on <span class="SimpleMath">\(X\)</span>.</p>
<h4>14.3 <span class="Heading">Computing a fundamental domain</span></h4>
<p>Explicit fundamental domains for certain values of <span class="SimpleMath
<p>More recently a <strong class="button">GAP</strong> implementation of Swan's algorithm has been included in <strong class="button">HAP</strong>. The implementation java.lang.StringIndexOutOfBoundsException: Index 169 out of bounds for length 0
<p><a id="X7A489A5D79DA9E5C" name="X7A489A5D79DA9E5C">involving of minimum radius 1/9java.lang.StringIndexOutOfBoundsException: Index 53 out of bounds for length 53
<h4>14.4 <span java.lang.StringIndexOutOfBoundsException: Index 17 out of bounds for length 0
<p>The fundamental domainjava.lang.StringIndexOutOfBoundsException: Range [6, 5) out of bounds for length 83
<java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
<div java.lang.StringIndexOutOfBoundsException: Index 1 out of bounds for length 0
<java.lang.StringIndexOutOfBoundsException: Range [81, 5) out of bounds for length 95 3-dimensional pem>usp vertex</em> of<span ="SimpleMath"\D)/> of =">\\)/s> : 2 they byred dots.Computer calculations show that these cusps lie in precisely three orbits under the action of <span class="SimpleMath">\(G_{-d}\)</span>. Thus, together with the orbit of <span class="SimpleMath">\(\infty\)</span> there are four distinct orbits of cusps. By the well-known correspondence between cusp orbits and elements of the class group it follows that the class group of <span class="SimpleMath">\(\mathbb Q(\sqrt{-39})\)</span> is of order <span class="SimpleMath">\(4\)</span>.</p>
and non-cuspidal vertices of minimum squared height 1/49 .
<span class="GAPprompt">gap<pan class="APprompt"gap&<spanspan=":=(D;/span>
<span class="GAPprompt">gap&java.lang.StringIndexOutOfBoundsException: Range [0, 30) out of bounds for length 0
/>/>
<p><img
<p>A
<p>The following additional commands comvert the Bianchi polyhedron <span class="SimpleMath">\(D\)</span> to a regular CW-java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
<div class="example"><pre>
<span class="div class="example<re>
<panclass"APprompt">gap&;/ span">:=D;<java.lang.StringIndexOutOfBoundsException: Index 92 out of bounds for length 92
Regular CW-complex of dimension 2
<span p><img src="images/bianchi3D22.png" align="center" height="550" alt="Fundamental domain for a Bianchi group"/> <img src=
</pre></div>
<p><img src="images/bianchi1skeleton.gif" align="center" java.lang.StringIndexOutOfBoundsException: Index 60 out of bounds for length 0
<p>A span class="GAP<><class"OQ,D<span
<div class="example"><pre>
="java.lang.StringIndexOutOfBoundsException: Range [28, 27) out of bounds for length 96
< java.lang.StringIndexOutOfBoundsException: Range [12, 11) out of bounds for length 86
<span class="GAPprompt">gap></span> <span class="GAPinput">Display2D(OQ,D);;<java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
<p><img src="images/bianchi3D163.png" align="center" height="550" alt="Fundamental domain for a Bianchi group"/> <img src=t testif theof waslarge.If testreturns thenyou\
<> is a orbit ofcuspsin this , orbit containing <span class="SimpleMath">\(\infty\)</span>, since <span class="SimpleMath">\(\mathbb Q(\sqrt{-163})\)</ich canbe edited inthe hap//bianchig .
<p>A fundamental domain for <span class="SimpleMath">\(G_{-33}\)</span> is visualizeddimensionalBianchi overOQ (
<div class="example"><pre
<java.lang.StringIndexOutOfBoundsException: Range [22, 5) out of bounds for length 96
<span class="GAPprompt">java.lang.StringIndexOutOfBoundsException: Index 26 out of bounds for length 0
<>a="78476F127B73BBD1"name"78476F127B73BBD1"<a<p
</>/>
<java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
<p><a id=java.lang.StringIndexOutOfBoundsException: Index 9 out of bounds for length 0
<java.lang.StringIndexOutOfBoundsException: Range [6, 2) out of bounds for length 611
<p>For a few values of <span class="SimpleMath">\ >apg;/ span =GAPinputC(R;<spanjava.lang.StringIndexOutOfBoundsException: Index 95 out of bounds for length 95
<div class="example"><pre>
<span class"GAPprompt">gap></span> <span class="GAPinput">P:=BianchiPolyhedron(-46);</span>
Try
:=BianchiPolyhedronO,N)
for java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
SwanBianchiCriterion(P);
to test if the value of N was large enough. If the test returns false then you\ 'll need to try a larger value of N.
A successful value<span class"">ap&;span>spanclass"APinput">[.0],-HomologyR,);/
ichcan edited manually the file /libCongruence/ianchi. .
<span class=" [ 2, 4, 12 ],,4,12],[ 2 ,2 ,[2,2 2, 12 ,[2 2 ,24 , 3-dimensional Bianchi polyhedron over OQ( Sqrt(
-))involving of squared 1/ 441 and non-cuspidal vertices of minimum squared
<h4>14.6 <span class="Heading">Computing a free resolution for <span class="SimpleMath">\(SL_2({\mathcal
<p>The above fundamental domains can be
<div class="example"><pre>
<span class="GAPprompt">gap></java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
<span class="GAPprompt">gap></span> <span class=p> commands the of orbits cusps i addition to the orbitofspan class"SimpleMath">\(\infty\)</span>). They determine that there is precisely one
<span>&;/><spanclass">([1.K.dimension()]-&tOrder(K!.stabilizer(0,k)));<span>
<span class="GAPprompt">gap></span> <span class="GAPinput">List([0..10],n->Homology(C,n));</span>
[ [ 0 ], [ 0, 0 ], [ 2, 2, 12, 0 ], [ 2, 2, 24 ], [ 2, 2 ],
[ 2, <classjava.lang.StringIndexOutOfBoundsException: Range [23, 22) out of bounds for length 128
<p>There is ample scope for bugs in the implementation of the above method for computing resolutions of Bianchi groups. The following sanity checks lend confidence to the implementation.</p>
<p>Let <span java.lang.StringIndexOutOfBoundsException: Range [0, 18) out of bounds for length 0
<p>One easy test to make in our computations is to check that the equivariant Euler characteristic of the <span class="SimpleMath">\(2\)</span>-complex is indeed java.lang.StringIndexOutOfBoundsException: Index 164 out of bounds for length 0
<h5>14.7-3 <span class="Heading">Compare different span class="GAPprompt">gap></span> <span class="GAPinput">List([0..9],n->Homology(TensorWithIntegers(R),n));< , ,,00] [, ,2 ,12, ,2 ,java.lang.StringIndexOutOfBoundsException: Index 74 out of bounds for length 74
<p>Sebastian Schoennenbeck in his thesis work computed some contractible <span class="SimpleMath">\(2\)</span>-complexes on which Bianchi groups act java.lang.StringIndexOutOfBoundsException: Index 152 out of bounds for length 0
<p>The following commands test span class="GAPprompt">gap>< G>ist[.9]n&;omologyTensorWithIntegers()n);<span>
<h5>14.7-4 <span class="Heading">Compare geometry to algebra</span></h5>
<java.lang.StringIndexOutOfBoundsException: Range [3, 2) out of bounds for length 502
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">K:=BianchiGcomplex(-23);;</span>
<span 6, 2, 2,4 infinity java.lang.StringIndexOutOfBoundsException: Index 34 out of bounds for length 34
</pre></div>
<p>A visualization of the fundamental domain tells us a certain amount about the algebra. In the case of <span class="SimpleMath">\(SL_2({\mathcal O}_{-23})\)</span></p>
<p>a span classjava.lang.StringIndexOutOfBoundsException: Range [23, 22) out of bounds for length 101
<div class="example"><>gapgt</java.lang.StringIndexOutOfBoundsException: Range [38, 37) out of bounds for length 77
< class"GAPprompt"gapgt;<spanspan"APinput"K=-23;<span
<span class="GAPprompt">gap></span> <span class="GAPinput">List([1..K
[, 4 ]
<p>Swan's reason for studying fundamental domains was to obtain explicit group presentations for <span class="SimpleMath">\(SL_2({\mathcal O}_{-d})\)</span> for various values of <span class="SimpleMath">\(d\)</span>. The following commands obtain a presentation for <span class="SimpleMath">\(SL_2({\mathcal O}_{-23})\)</span>.</p>
<hr />
<pclass="foot">generated by < href="https:/www..rwthaachen.de/~Frank.Luebeck/GAPDoc">GAPDoc2HTML</a></p>
</body>
</html>
Messung V0.5 in Prozent
¤ Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.0.18Bemerkung:
¤
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung und die Messung sind noch experimentell.