Polynomial matrix - Revision history

en>Michael Hardy: /* Properties */

2014-06-16T03:01:18Z

Properties

← Older revision		Revision as of 05:01, 16 June 2014
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	~~In [[model theory]], a '''weakly o-minimal structure''' is a model theoretic [[Structure (mathematical logic)\| structure]] whose definable sets in~~ the ~~domain are just finite unions of convex sets.~~		The name of the writer is Garland. Bookkeeping is what he does. The factor she adores most is to perform handball but she can't make it her profession. Her family lives in Idaho.<br><br>Here is my web page ... [http://Blogzaa.com/blogs/post/14073 Blogzaa.com]

	~~==Definition==~~
	~~A [[Total order\|linearly ordered]] structure, ''M'', with language ''L'' including an ordering relation <,~~ is ~~called weakly o-minimal if every parametrically definable subset of ''M'' is a finite union of convex (definable) subsets~~. ~~A theory~~ is ~~weakly o-minimal if all its models are weakly o-minimal~~.

	~~Note that, in contrast to [[o-minimality]], it~~ is ~~possible for a theory~~ to ~~have models which are weakly o-minimal and to have other models which are not weakly o-minimal.<ref>M.A.Dickmann,~~ '~~'Elimination of Quantifiers for Ordered Valuation Rings'', The Journal of symbolic Logic, Vol~~. ~~52, No. 1 (Mar., 1987), pp 116-128. [http://www.jstor.org/view/00224812/di985230/98p04615/0]</ref>~~

	~~==Difference from o-minimality==~~
	~~In an o-minimal structure (''M'',<,...) the definable sets~~ in ~~''M'' are finite unions of points and intervals, an interval here being a set of the form~~

	~~:<math>I=\{r\in M\,:\,a<r<b\}</math>~~

	~~for some (possibly infinite) constants ''a'' and ''b'' in ''M''~~.<~~ref~~>~~"Infinite" here simply refers to the two extra points added to ''M'' that act as lower and upper bounds, usually denoted −∞ and +∞.~~<~~/ref~~> ~~For weakly o-minimal structures (''m'',<,...) this~~ is ~~relaxed so that the definable sets in ''m'' are finite unions of convex sets~~. ~~A set ''C'' is convex if whenever ''a'' and ''b'' are in ''C'' with ''a'' < ''b'' and ''c'' ∈ ''m'' satisfies ''a'' < ''c'' < ''b'', then ''c'' is in ''C''~~.

	~~On the face of it, convex sets are just intervals, in which case weakly o-minimal structures would just be o-minimal structures~~. And indeed, if we have a weakly o-minimal structure expanding ('''R''',<), the real ordered field, then this structure will be o-minimal. The two notions are different in other settings though. For example, let ''R'' be the ordered field of real [[algebraic number]]s with the usual ordering < inherited from '''R'''. Take a transcendental number, say ''[[Pi\|π]]'', and add a [[unary relation]] ''S'' to the structure given by the subset (−''π'',''π'') ∩ ''R''. Now consider the subset ''A'' of ''R'' defined by the formula

	:~~<math>0<a \,\wedge\, S(a)<~~/~~math>~~

	~~so that the set consists of all strictly positive real algebraic numbers that are less than ''π''~~. The set is clearly convex, but cannot be written as a finite union of points and intervals whose endpoints are in ''R''. To write it as an interval one would either have to include the endpoint ''π'', which isn't in ''R'', or one would require infinitely many intervals, such as the union

	~~:<math>\bigcup_{\alpha<\pi}(0,\alpha).<~~/~~math>~~

	Since we have a definable set that isn't a finite union of points and intervals, this structure is not o-minimal. However, it is known that the structure is weakly o-minimal, and in fact the theory of this structure is weakly o-minimal.<ref>D. Macpherson, D. Marker, C. Steinhorn, ''Weakly o-minimal structures and real closed fields'', Trans. Amer. Math. Soc. '''352''' (2000), no. 12, pp.~~5435–5483, {{MathSciNet \| id = 1781273}}.</ref>~~

	~~== Notes ==~~
	~~{{Reflist}}~~

	~~[[Category:Model theory]]~~
	~~[[Category:Mathematical structures]~~]

en>Mark viking: /* Properties */ Added wl

2013-09-06T05:47:27Z

Properties: Added wl

← Older revision		Revision as of 07:47, 6 September 2013
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	I'~~m Luther but I never really liked that title~~. ~~My occupation~~ is a ~~messenger~~. ~~Camping~~ is ~~some thing~~ that I'~~ve carried out~~ for ~~many years~~. ~~Her spouse~~ and ~~her selected to reside~~ in ~~Alabama~~.<br><br>~~my webpage :: extended auto warranty~~ ([~~http~~://~~help~~.~~ksu~~.~~Edu~~.sa/~~node/63594 Recommended Internet site~~])		In [[model theory]], a '''weakly o-minimal structure''' is a model theoretic [[Structure (mathematical logic)\| structure]] whose definable sets in the domain are just finite unions of convex sets.

			==Definition==
			A [[Total order\|linearly ordered]] structure, ''M'', with language ''L'' including an ordering relation <, is called weakly o-minimal if every parametrically definable subset of ''M'' is a finite union of convex (definable) subsets. A theory is weakly o-minimal if all its models are weakly o-minimal.

			Note that, in contrast to [[o-minimality]], it is possible for a theory to have models which are weakly o-minimal and to have other models which are not weakly o-minimal.<ref>M.A.Dickmann, ''Elimination of Quantifiers for Ordered Valuation Rings'', The Journal of symbolic Logic, Vol. 52, No. 1 (Mar., 1987), pp 116-128. [http://www.jstor.org/view/00224812/di985230/98p04615/0]</ref>

			==Difference from o-minimality==
			In an o-minimal structure (''M'',<,...) the definable sets in ''M'' are finite unions of points and intervals, an interval here being a set of the form

			:<math>I=\{r\in M\,:\,a<r<b\}</math>

			for some (possibly infinite) constants ''a'' and ''b'' in ''M''.<ref>"Infinite" here simply refers to the two extra points added to ''M'' that act as lower and upper bounds, usually denoted −∞ and +∞.</ref> For weakly o-minimal structures (''m'',<,...) this is relaxed so that the definable sets in ''m'' are finite unions of convex sets. A set ''C'' is convex if whenever ''a'' and ''b'' are in ''C'' with ''a'' < ''b'' and ''c'' ∈ ''m'' satisfies ''a'' < ''c'' < ''b'', then ''c'' is in ''C''.

			On the face of it, convex sets are just intervals, in which case weakly o-minimal structures would just be o-minimal structures. And indeed, if we have a weakly o-minimal structure expanding ('''R''',<), the real ordered field, then this structure will be o-minimal. The two notions are different in other settings though. For example, let ''R'' be the ordered field of real [[algebraic number]]s with the usual ordering < inherited from '''R'''. Take a transcendental number, say ''[[Pi\|π]]'', and add a [[unary relation]] ''S'' to the structure given by the subset (−''π'',''π'') ∩ ''R''. Now consider the subset ''A'' of ''R'' defined by the formula

			:<math>0<a \,\wedge\, S(a)</math>

			so that the set consists of all strictly positive real algebraic numbers that are less than ''π''. The set is clearly convex, but cannot be written as a finite union of points and intervals whose endpoints are in ''R''. To write it as an interval one would either have to include the endpoint ''π'', which isn't in ''R'', or one would require infinitely many intervals, such as the union

			:<math>\bigcup_{\alpha<\pi}(0,\alpha).</math>

			Since we have a definable set that isn't a finite union of points and intervals, this structure is not o-minimal. However, it is known that the structure is weakly o-minimal, and in fact the theory of this structure is weakly o-minimal.<ref>D. Macpherson, D. Marker, C. Steinhorn, ''Weakly o-minimal structures and real closed fields'', Trans. Amer. Math. Soc. '''352''' (2000), no. 12, pp.5435–5483, {{MathSciNet \| id = 1781273}}.</ref>

			== Notes ==
			{{Reflist}}

			[[Category:Model theory]]
			[[Category:Mathematical structures]]

en>Qetuth: more specific stub type + intro link

2012-01-01T15:08:53Z

more specific stub type + intro link

New page

I'm Luther but I never really liked that title. My occupation is a messenger. Camping is some thing that I've carried out for many years. Her spouse and her selected to reside in Alabama.<br><br>my webpage :: extended auto warranty ([http://help.ksu.Edu.sa/node/63594 Recommended Internet site])