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In [[mathematics]], the '''Markov–Kakutani fixed-point theorem''', named after [[Andrey Markov, Jr.|Andrey Markov]] and [[Shizuo Kakutani]], states that a commuting family of continuous [[affine transformation|affine self-mappings]] of a [[convex set|compact convex subset]] in a [[locally convex topological vector space]] has a common fixed point. | |||
==Statement== | |||
Let ''E'' be a locally convex topological vector space. Let ''C'' be a compact convex subset of ''E''. | |||
Let ''S'' be a commuting family of self-mappings ''T'' of ''C'' which are continuous and affine, i.e. | |||
''T''(''tx'' +(1 – ''t'')''y'') = ''tT''(''x'') + (1 – ''t'')''T''(''y'') for ''t'' in [0,1] and ''x'', ''y'' in ''C''. Then the mappings have a common fixed point in ''C''. | |||
==Proof for a single affine self-mapping== | |||
Let ''T'' be a continuous affine self-mapping of ''C''. | |||
For ''x'' in ''C'' define other elements of ''C'' by | |||
:<math> x(N)={1\over N+1}\sum_{n=0}^N T^n(x). </math> | |||
Since ''C'' is compact, there is a convergent subsequence in ''C'': | |||
:<math> x(N_i)\rightarrow y. \,</math> | |||
To prove that ''y'' is a fixed point, it suffices to show that ''f''(''Ty'') = ''f''(''y'') for every ''f'' in the dual of ''E''. Since ''C'' is compact, |''f''| is bounded on ''C'' by a positive constant ''M''. On the other hand | |||
:<math> |f(Tx(N))-f(x(N))|={1\over N+1} |f(T^{N+1}x)-f(x)|\le {2M\over N+1}. </math> | |||
Taking ''N'' = ''N''<sub>''i''</sub> and passing to the limit as ''i'' goes to infinity, it follows that | |||
:<math> f(Ty) = f(y). \, </math> | |||
Hence | |||
:<math>Ty = y. \, </math> | |||
==Proof of theorem== | |||
The set of fixed points of a single affine mapping ''T'' is a non-empty compact convex set ''C''<sup>''T''</sup> by the result for a single mapping. The other mappings in the family ''S'' commute with ''T'' so leave ''C''<sup>''T''</sup> invariant. Applying the result for a single mapping successively, it follows that any finite subset of ''S'' has a non-empty fixed point set given as the intersection of the compact convex sets ''C''<sup>''T''</sup> as ''T'' ranges over the subset. From the [[finite intersection property|compactness]] of ''C'' it follows that the set | |||
:<math> C^S=\{y\in C|Ty=y, \, y\in S\}=\bigcap_{T\in S} C^T \,</math> | |||
is non-empty (and compact and convex). | |||
==References== | |||
*{{citation|first=A.|last=Markov|title=Quelques théorèmes sur les ensembles abéliens|journal=Dokl. Akad. Nauk. SSSR|year=1936|volume=10|pages=311–314}} | |||
*{{citation|first=S.|last=Kakutani|title=Two fixed point theorems concerning bicompact convex sets|year=1938|volume=14|pages=242–245|journal=Proc. Imp. Akad. Tokyo}} | |||
*{{citation|first=M.|last=Reed|first2=B.|last2=Simon|title=Functional Analysis|series=Methods of Mathematical Physics|volume=1| edition=2nd revised|publisher=Academic Press|year=1980|isbn=0-12-585050-6|page=152}} | |||
{{DEFAULTSORT:Markov-Kakutani fixed-point theorem}} | |||
[[Category:Fixed-point theorems]] | |||
[[Category:Functional analysis]] | |||
[[Category:Mathematical theorems]] |
Revision as of 11:30, 20 August 2013
In mathematics, the Markov–Kakutani fixed-point theorem, named after Andrey Markov and Shizuo Kakutani, states that a commuting family of continuous affine self-mappings of a compact convex subset in a locally convex topological vector space has a common fixed point.
Statement
Let E be a locally convex topological vector space. Let C be a compact convex subset of E. Let S be a commuting family of self-mappings T of C which are continuous and affine, i.e. T(tx +(1 – t)y) = tT(x) + (1 – t)T(y) for t in [0,1] and x, y in C. Then the mappings have a common fixed point in C.
Proof for a single affine self-mapping
Let T be a continuous affine self-mapping of C.
For x in C define other elements of C by
Since C is compact, there is a convergent subsequence in C:
To prove that y is a fixed point, it suffices to show that f(Ty) = f(y) for every f in the dual of E. Since C is compact, |f| is bounded on C by a positive constant M. On the other hand
Taking N = Ni and passing to the limit as i goes to infinity, it follows that
Hence
Proof of theorem
The set of fixed points of a single affine mapping T is a non-empty compact convex set CT by the result for a single mapping. The other mappings in the family S commute with T so leave CT invariant. Applying the result for a single mapping successively, it follows that any finite subset of S has a non-empty fixed point set given as the intersection of the compact convex sets CT as T ranges over the subset. From the compactness of C it follows that the set
is non-empty (and compact and convex).
References
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Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010