Sahlqvist formula: Difference between revisions

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In [[mathematics]], a source for the [[representation theory]] of the [[group (mathematics)|group]] of [[diffeomorphism]]s of a [[smooth manifold]] ''M'' is the initial observation that (for ''M'' connected) that group acts transitively on ''M''.
 
==History==
 
A survey paper from 1975 of the subject by [[Anatoly Vershik]], [[Israel Gelfand]] and [[M. I. Graev]] attributes the original interest in the topic to research in [[theoretical physics]] of the [[local current algebra]], in the preceding years. Research on the ''finite configuration'' representations was in papers of [[R. S. Ismagilov]] (1971), and [[A. A. Kirillov]] (1974). The representations of interest in physics are described as a [[cross product (ring theory)|cross product]] ''C''<sup></sup>(''M'')·Diff(''M'').
 
==Constructions==
 
Let therefore ''M'' be a ''n''-dimensional [[connected space|connected]] [[differentiable manifold]], and ''x'' be any point on it. Let Diff(''M'') be the orientation-preserving [[diffeomorphism group]] of ''M'' (only the [[identity component]] of mappings [[homotopic]] to the identity diffeomorphism if you wish) and Diff<sub>''x''</sub><sup>1</sup>(''M'') the [[stabilizer (group theory)|stabilizer]] of ''x''. Then, ''M'' is identified as a [[homogeneous space]]
 
:Diff(''M'')/Diff<sub>''x''</sub><sup>1</sup>(''M'').
 
From the algebraic point of view instead, <math>C^\infty(M)</math> is the [[associative algebra|algebra]] of [[smooth function]]s over ''M'' and <math>I_x(M)</math> is the [[ideal]] of smooth functions vanishing at ''x''. Let <math>I_x^n(M)</math> be the ideal of smooth functions which vanish up to the n-1th [[partial derivative]] at ''x''. <math>I_x^n(M)</math> is invariant under the group Diff<sub>''x''</sub><sup>1</sup>(''M'') of diffeomorphisms fixing x. For ''n'' > 0 the group Diff<sub>''x''</sub><sup>''n''</sup>(''M'') is defined as the [[subgroup]] of Diff<sub>''x''</sub><sup>1</sup>(''M'') which acts as the identity on <math>I_x(M)/I_x^n(M)</math>. So, we have a descending chain
 
:Diff(''M'') &sup; Diff<sub>''x''</sub><sup>1</sup>(M) &sup; ... &sup; Diff<sub>''x''</sub><sup>''n''</sup>(''M'') &sup; ...
 
Here Diff<sub>''x''</sub><sup>''n''</sup>(''M'') is a [[normal subgroup]] of Diff<sub>''x''</sub><sup>1</sup>(''M''), which means we can look at the [[quotient group]]
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>''n''</sup>(''M'').
 
Using [[harmonic analysis]], a real- or complex-valued function (with some sufficiently nice topological properties) on the diffeomorphism group can be [[decompose]]d into Diff<sub>''x''</sub><sup>1</sup>(''M'') representation-valued functions over ''M''.
 
==The supply of representations==
 
So what are the reps of Diff<sub>''x''</sub><sup>1</sup>(''M'')? Let's use the fact that if we have a [[group homomorphism]] φ:''G'' → ''H'', then if we have a ''H''-representation, we can obtain a restricted ''G''-representation. So, if we have a rep of
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>''n''</sup>(''M''),
 
we can obtain a rep of Diff<sub>''x''</sub><sup>1</sup>(''M'').
 
Let's look at
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>2</sup>(''M'')
 
first. This is [[isomorphic]] to the [[general linear group]] GL<sup>+</sup>(''n'', '''R''') (and because we're only considering orientation preserving diffeomorphisms and so the determinant is positive). What are the reps of GL<sup>+</sup>(''n'', '''R''')?
 
:<math>GL^+(n,\mathbb{R})\cong \mathbb{R}^+\times SL(n,\mathbb{R})</math>.
 
We know the reps of SL(''n'', '''R''') are simply [[tensor]]s over ''n'' dimensions. How about the '''R'''<sup>+</sup> part? That corresponds to the ''density'', or in other words, how the tensor rescales under the [[determinant]] of the [[Jacobian]] of the diffeomorphism at ''x''. (Think of it as the [[conformal weight]] if you will, except that there is no conformal structure here). (Incidentally, there is nothing preventing us from having a complex density).
 
So, we have just discovered the tensor reps (with density) of the diffeomorphism group.
 
Let's look at
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>''n''</sup>(''M'').
 
This is a finite-dimensional group. We have the chain
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>1</sup>(''M'') &sub; ... &sub; Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>''n''</sup>(''M'') &sub; ...
 
Here, the "&sub;" signs should really be read to mean an injective homomorphism, but since it is canonical, we can pretend these quotient groups are embedded one within the other.
 
Any rep of
 
:Diff<sub>''x''</sub><sup>1</sup>(''M'')/Diff<sub>''x''</sub><sup>''m''</sup>(''M'')
 
can automatically be turned into a rep of
 
:Diff<sub>''x''</sub><sup>1</sup>/Diff<sub>''x''</sub><sup>''n''</sup>(''M'')
 
if ''n'' > ''m''. Let's say we have a rep of
 
:Diff<sub>''x''</sub><sup>1</sup>/Diff<sub>''x''</sub><sup>''p'' + 2</sup>
 
which doesn't arise from a rep of
 
:Diff<sub>''x''</sub><sup>1</sup>/Diff<sub>''x''</sub><sup>''p'' + 1</sup>.
 
Then, we call the [[fiber bundle]] with that rep as the [[fiber]] (i.e. Diff<sub>''x''</sub><sup>1</sup>/Diff<sub>''x''</sub><sup>''p'' + 2</sup> is the [[structure group]]) a '''[[jet bundle]]''' of order ''p''.
 
Side remark: This is really the method of [[induced representation]]s with the smaller group being Diff<sub>x</sub><sup>1</sup>(M) and the larger group being Diff(''M'').
 
==Intertwining structure==
 
In general, the space of sections of the tensor and jet bundles would be an irreducible representation and we often look at a subrepresentation of them. We can study the structure of these reps through the study of the [[intertwiner]]s between them.
 
If the fiber is not an irreducible representation of Diff<sub>''x''</sub><sup>1</sup>(''M''), then we can have a nonzero intertwiner mapping each fiber pointwise into a smaller [[quotient representation]]. Also, the [[exterior derivative]] is an intertwiner from the space of [[differential form]]s to another of higher order. (Other derivatives are not, because [[connection (mathematics)|connections]] aren't invariant under diffeomorphisms, though they are [[Covariance|covariant]].) The [[partial derivative]] isn't diffeomorphism invariant. There is a derivative intertwiner taking sections of a jet bundle of order ''p'' into sections of a jet bundle of order ''p''&nbsp;+&nbsp;1.
 
[[Category:Diffeomorphisms]]
[[Category:Representation theory of groups]]

Latest revision as of 16:57, 27 June 2014

Let's look an actual registry scan and a few of what you will see whenever we do one on a computer. This test was done on a computer that was not working as it could, running at slow speed and having some issues with freezing up.

So 1 day my computer suddenly started being strange. I was so frustrated, because my files were missing, and I cannot open the files that I needed, plus then, suddenly, everything stopped working!

With the Internet, the risk to your registry is much more and windows XP error messages might appear frequently. Why? The malicious wares like viruses, Trojans, spy-wares, ad wares, and the like gets recorded too. Cookies are perfect examples. We reach save passwords, plus stuff, right? That is a easy illustration of the register working.

It is usual which the imm32.dll error is caused as a result of a mis-deletion activity. If you cannot find the imm32.dll anywhere on your computer, there is not any doubt that it should be mis-deleted whenever uninstalling programs or other unneeded files. Hence, you are able to directly cope it from other programs or download it from a secure web plus then place it on a computer.

When it comes to software, this is the vital piece because it is the 1 running your system plus alternative programs required in your functions. Always maintain the cleanliness of your program from obsolete information by getting a wise tuneup utilities 2014. Protect it from a virus on the net by providing a workable virus security program. You could have a monthly clean up by running a defragmenter program. This means it can enhance the performance of the computer plus for we to avoid any mistakes. If you think something is wrong with the computer software, and we don't recognize how to fix it then refer to a technician.

Your system is made plus built for the purpose of helping you accomplish tasks plus not be pestered by windows XP error messages. When there are mistakes, what do we do? Some folks pull their hair plus cry, while those sane ones have their PC repaired, whilst those really wise ones analysis to have the errors fixed themselves. No, these errors were not moreover tailored to rob you off your money plus time. There are points which you can do to really prevent this from happening.

The 'registry' is just the central database that shops all a settings plus choices. It's a actually important piece of the XP program, meaning which Windows is continually adding plus updating the files inside it. The difficulties occur when Windows really corrupts & loses a few of these files. This makes a computer run slow, as it tries difficult to obtain them again.

There are numerous firms that offer the service of troubleshooting a PC each time we call them, all you need to do is sign up with them and for a small fee, we could have your machine usually functioning perfectly plus serve you greater.