View source for 9-simplex

{| class="wikitable" align="right" style="margin-left:10px" width="250"
!bgcolor=#e7dcc3 colspan=2|Regular decayotton<BR>(9-simplex)
|-
|bgcolor=#ffffff align=center colspan=2|[[Image:9-simplex_t0.svg|280px]]<BR>Orthogonal projection<BR>inside [[Petrie polygon]]
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|bgcolor=#e7dcc3|Type||Regular 9-polytope
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|bgcolor=#e7dcc3|Family||[[Simplex|simplex]]
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|bgcolor=#e7dcc3|[[Schläfli symbol]]|| {3,3,3,3,3,3,3,3}
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|bgcolor=#e7dcc3|Coxeter-Dynkin diagram||{{CDD|node_1|3|node|3|node|3|node|3|node|3|node|3|node|3|node|3|node}}
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|bgcolor=#e7dcc3|8-faces||10 8-simplex[[Image:8-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|7-faces||45 [[7-simplex|7-simplex]][[Image:7-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|6-faces||120 [[6-simplex|6-simplex]][[Image:6-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|5-faces||210 [[5-simplex|5-simplex]][[Image:5-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|4-faces||252 [[5-cell|5-cell]][[Image:4-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|Cells||210 [[Tetrahedron|tetrahedron]][[Image:3-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|Faces||120 [[Triangle|triangle]][[Image:2-simplex_t0.svg|25px]]
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|bgcolor=#e7dcc3|Edges||45
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|bgcolor=#e7dcc3|Vertices||10
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|bgcolor=#e7dcc3|[[Vertex figure]]||8-simplex
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|bgcolor=#e7dcc3|[[Petrie polygon]]||[[Decagon|decagon]]
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|bgcolor=#e7dcc3|[[Coxeter group]]|| A<sub>9</sub> [3,3,3,3,3,3,3,3]
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|bgcolor=#e7dcc3|Dual||Self-dual
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|bgcolor=#e7dcc3|Properties||[[Convex polytope|convex]]
|}
In [[Geometry|geometry]], a 9-[[Simplex|simplex]] is a self-dual [[Regular polytope|regular]] 9-polytope. It has 10 [[Vertex (geometry)|vertices]], 45 [[Edge (geometry)|edge]]s, 120 triangle [[Face (geometry)|faces]], 210 tetrahedral cells, 252 [[5-cell|5-cell]] 4-faces, 210 [[5-simplex|5-simplex]] 5-faces, 120 [[6-simplex|6-simplex]] 6-faces, 45 [[7-simplex|7-simplex]] 7-faces, and 10 8-simplex 8-faces.  Its [[Dihedral angle|dihedral angle]] is cos<sup>−1</sup>(1/9), or approximately 83.62°.

It can also be called a '''decayotton''', or '''deca-9-tope''', as a 10-[[Facet (geometry)|facetted]] polytope in 9-dimensions.. The [[5-polytope#A note on generality of terms for n-polytopes and elements|name]] ''decayotton'' is derived from ''deca'' for ten facets in [[Social:Greek language|Greek]] and yotta (a variation of "oct" for eight), having 8-dimensional facets, and ''-on''.

== Coordinates ==

The Cartesian coordinates of the vertices of an origin-centered regular decayotton having edge length&nbsp;2 are:

:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ \sqrt{1/21},\ \sqrt{1/15},\ \sqrt{1/10},\ \sqrt{1/6},\ \sqrt{1/3},\ \pm1\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ \sqrt{1/21},\ \sqrt{1/15},\ \sqrt{1/10},\ \sqrt{1/6},\ -2\sqrt{1/3},\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ \sqrt{1/21},\ \sqrt{1/15},\ \sqrt{1/10},\ -\sqrt{3/2},\ 0,\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ \sqrt{1/21},\ \sqrt{1/15},\ -2\sqrt{2/5},\ 0,\ 0,\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ \sqrt{1/21},\ -\sqrt{5/3},\ 0,\ 0,\ 0,\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ \sqrt{1/28},\ -\sqrt{12/7},\ 0,\ 0,\ 0,\ 0,\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ 1/6,\ -\sqrt{7/4},\ 0,\ 0,\ 0,\ 0,\ 0,\ 0\right)</math>
:<math>\left(\sqrt{1/45},\ -4/3,\ 0,\ 0,\ 0,\ 0,\ 0,\ 0,\ 0\right)</math>
:<math>\left(-3\sqrt{1/5},\ 0,\ 0,\ 0,\ 0,\ 0,\ 0,\ 0,\ 0\right)</math>

More simply, the vertices of the ''9-simplex'' can be positioned in 10-space as permutations of (0,0,0,0,0,0,0,0,0,1). These are the vertices of one [[Facet (geometry)|Facet]] of the [[10-orthoplex|10-orthoplex]].

== Images ==


== References==
* [[Biography:Harold Scott MacDonald Coxeter|Coxeter, H.S.M.]]: 
** {{cite book |title-link=Regular Polytopes (book) |author-mask=1 |first=H.S.M. |last=Coxeter |chapter=Table I (iii): Regular Polytopes, three regular polytopes in n-dimensions (n≥5) |title=Regular Polytopes |publisher=Dover |edition=3rd |year=1973 |isbn=0-486-61480-8 |pages=296 }}
** {{cite book |editor-first=F. Arthur |editor-last=Sherk |editor2-first=Peter |editor2-last=McMullen |editor3-first=Anthony C. |editor3-last=Thompson |editor4-first=Asia Ivic |editor4-last=Weiss |title=Kaleidoscopes: Selected Writings of H.S.M. Coxeter |publisher=Wiley  |year=1995 |isbn=978-0-471-01003-6 |url=https://books.google.com/books?id=fUm5Mwfx8rAC&pg=PP1}}
*** (Paper 22) {{cite journal |author-mask=1 |first=H.S.M. |last=Coxeter |title=Regular and Semi Regular Polytopes I |journal=Math. Zeit. |volume=46 |pages=380–407 |year=1940 |doi=10.1007/BF01181449 |s2cid=186237114 |url=https://books.google.com/books?id=fUm5Mwfx8rAC&pg=PA251 }}
*** (Paper 23) {{cite journal |author-mask=1 |first=H.S.M. |last=Coxeter |title=Regular and Semi-Regular Polytopes II |journal=Math. Zeit. |volume=188 |pages=559–591 |year=1985 |issue=4 |doi=10.1007/BF01161657 |s2cid=120429557 |url=https://books.google.com/books?id=fUm5Mwfx8rAC&pg=PA279}}
*** (Paper 24) {{cite journal |author-mask=1 |first=H.S.M. |last=Coxeter |title=Regular and Semi-Regular Polytopes III |journal=Math. Zeit. |volume=200 |pages=3–45 |year=1988 |doi=10.1007/BF01161745 |s2cid=186237142 |url=https://books.google.com/books?id=fUm5Mwfx8rAC&pg=PA313}}
* {{cite book |first1=John H. |last1=Conway |first2=Heidi |last2=Burgiel |first3=Chaim |last3=Goodman-Strauss |chapter=26. Hemicubes: 1<sub>n1</sub> |title=The Symmetries of Things |year=2008 |isbn=978-1-56881-220-5 |pages=409 }}
* {{citation |first=Norman |last=Johnson |title=Uniform Polytopes |date=1991 |type=Manuscript }}
**  {{cite thesis |first=N.W. |last=Johnson |title=The Theory of Uniform Polytopes and Honeycombs |date=1966 |type=PhD |publisher=University of Toronto |url=https://search.library.utoronto.ca/details?402790 |oclc=258527038}}
* {{KlitzingPolytopes|polyyotta.htm|9D uniform polytopes (polyyotta)|x3o3o3o3o3o3o3o3o — day}}

== External links ==
* {{PolyCell | urlname = glossary.html| title = Glossary for hyperspace}}
* [http://www.polytope.net/hedrondude/topes.htm Polytopes of Various Dimensions]
* [http://tetraspace.alkaline.org/glossary.htm Multi-dimensional Glossary]

[[Category:9-polytopes]]
{{Polytopes}}

{{Sourceattribution|9-simplex}}