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In [[mathematics]], '''hyperfunctions''' are generalizations of functions, as a 'jump' from one [[holomorphic function]] to another at a boundary, and can be thought of informally as [[Distribution (mathematics)|distribution]]s of infinite order. Hyperfunctions were introduced by [[Mikio Sato]] in 1958, building upon earlier work by [[Alexander Grothendieck|Grothendieck]] and others. In Japan, it is usually called the '''Sato's hyperfuncion''' with the name of M. Sato. | |||
== Formulation == | |||
A hyperfunction on the real line can be conceived of as the 'difference' between one holomorphic function defined on the upper half-plane and another on the lower half-plane. That is, a hyperfunction is specified by a pair (''f'', ''g''), where ''f'' is a holomorphic function on the upper half-plane and ''g'' is a holomorphic function on the lower half-plane. | |||
Informally, the hyperfunction is what the difference ''f'' − ''g'' would be at the real line itself. This difference is not affected by adding the same holomorphic function to both ''f'' and ''g'', so if h is a holomorphic function on the whole [[complex plane]], the hyperfunctions (''f'', ''g'') and (''f'' + ''h'', ''g'' + ''h'') are defined to be equivalent. | |||
===Definition in one dimension=== | |||
The motivation can be concretely implemented using ideas from [[sheaf cohomology]]. Let <math>\mathcal{O}</math> be the [[sheaf (mathematics)|sheaf]] of [[holomorphic function]]s on '''C'''. Define the hyperfunctions on the [[real line]] by | |||
:<math>\mathcal{B}(\mathbf{R}) = H^1_{\mathbf{R}}(\mathbf{C}, \mathcal{O}),</math> | |||
the first [[local cohomology]] group. | |||
Concretely, let '''C'''<sup>+</sup> and '''C'''<sup>−</sup> | |||
be the [[upper half-plane]] and [[lower half-plane]] respectively. Then | |||
:<math>\mathbf{C}^+ \cup \mathbf{C}^- = \mathbf{C} \setminus \mathbf{R}.\,</math> | |||
so | |||
:<math>H^1_{\mathbf{R}}(\mathbf{C}, \mathcal{O}) = \left [ H^0(\mathbf{C}^+, \mathcal{O}) \oplus H^0(\mathbf{C}^-, \mathcal{O}) \right ] /H^0(\mathbf{C}, \mathcal{O}).</math> | |||
Since the zeroth cohomology group of any sheaf is simply the global sections of that sheaf, we see that a hyperfunction is a pair of holomorphic functions one each on the upper and lower complex halfplane modulo entire holomorphic functions. | |||
== Examples == | |||
*If ''f'' is any holomorphic function on the whole complex plane, then the restriction of ''f'' to the real axis is a hyperfunction, represented by either (''f'', 0) or (0, −''f''). | |||
*The [[Heaviside step function]] can be represented as <math>H(x) = \left(\frac{1}{2\pi i}\log(z),\frac{1}{2\pi i}\log(z)-1\right)</math>. | |||
*The [[Dirac delta function|Dirac delta "function"]] is represented by <math>\left(\frac{1}{2\pi iz},\frac{1}{2\pi iz}\right)</math>. This is really a restatement of [[Cauchy's integral formula]]. To verify it one can calculate the integration of ''f'' just below the real line, and subtract integration of ''g'' just above the real line - both from left to right. Note that the hyperfunction can be non-trivial, even if the components are analytic continuation of the same function. Also this can be easily checked by differentiating the Heaviside function. | |||
*If ''g'' is a [[continuous function]] (or more generally a distribution) on the real line with support contained in a bounded interval ''I'', then ''g'' corresponds to the hyperfunction (''f'', −''f''), where ''f'' is a holomorphic function on the complement of ''I'' defined by | |||
::<math> f(z)={1\over 2\pi i}\int_{x\in I} g(x){dx\over z-x}.</math> | |||
:This function ''f '' jumps in value by ''g''(''x'') when crossing the real axis at the point ''x''. The formula for ''f'' follows from the previous example by writing ''g'' as the [[convolution]] of itself with the Dirac delta function. | |||
*If ''f'' is any function that is holomorphic everywhere except for an [[essential singularity]] at 0 (for example, ''e''<sup>1/''z''</sup>), then (''f'', −''f'') is a hyperfunction with support 0 that is not a distribution. If ''f'' has a pole of finite order at 0 then (''f'', −''f'') is a distribution, so when ''f'' has an essential singularity then (''f'',−''f'') looks like a "distribution of infinite order" at 0. (Note that distributions always have ''finite'' order at any point.) | |||
==See also== | |||
* [[hypersurface]] | |||
== References == | |||
* {{citation|last=Hörmander|first=Lars|authorlink=Lars Hörmander|title=The analysis of linear partial differential operators, Volume I: Distribution theory and Fourier analysis|publisher=Springer-Verlag|publication-place=Berlin|year=2003|isbn=3-540-00662-1}}. | |||
* {{citation|last=Sato|first=Mikio|authorlink=Mikio Sato|title=Theory of Hyperfunctions, I|id={{hdl|2261/6027}}|journal=Journal of the Faculty of Science, University of Tokyo. Sect. 1, Mathematics, astronomy, physics, chemistry|volume=8|year=1959|issue=1|pages=139–193|mr=0114124}}. | |||
* {{citation|last=Sato|first=Mikio|authorlink=Mikio Sato|title=Theory of Hyperfunctions, II|id={{hdl|2261/6031}}|journal=Journal of the Faculty of Science, University of Tokyo. Sect. 1, Mathematics, astronomy, physics, chemistry|volume=8|year=1960|issue=2|pages=387–437|mr=0132392}}. | |||
[[Category:Algebraic analysis]] | |||
[[Category:Complex analysis]] | |||
[[Category:Generalized functions]] | |||
[[Category:Sheaf theory]] |
Revision as of 09:33, 13 September 2013
In mathematics, hyperfunctions are generalizations of functions, as a 'jump' from one holomorphic function to another at a boundary, and can be thought of informally as distributions of infinite order. Hyperfunctions were introduced by Mikio Sato in 1958, building upon earlier work by Grothendieck and others. In Japan, it is usually called the Sato's hyperfuncion with the name of M. Sato.
Formulation
A hyperfunction on the real line can be conceived of as the 'difference' between one holomorphic function defined on the upper half-plane and another on the lower half-plane. That is, a hyperfunction is specified by a pair (f, g), where f is a holomorphic function on the upper half-plane and g is a holomorphic function on the lower half-plane.
Informally, the hyperfunction is what the difference f − g would be at the real line itself. This difference is not affected by adding the same holomorphic function to both f and g, so if h is a holomorphic function on the whole complex plane, the hyperfunctions (f, g) and (f + h, g + h) are defined to be equivalent.
Definition in one dimension
The motivation can be concretely implemented using ideas from sheaf cohomology. Let be the sheaf of holomorphic functions on C. Define the hyperfunctions on the real line by
the first local cohomology group.
Concretely, let C+ and C− be the upper half-plane and lower half-plane respectively. Then
so
Since the zeroth cohomology group of any sheaf is simply the global sections of that sheaf, we see that a hyperfunction is a pair of holomorphic functions one each on the upper and lower complex halfplane modulo entire holomorphic functions.
Examples
- If f is any holomorphic function on the whole complex plane, then the restriction of f to the real axis is a hyperfunction, represented by either (f, 0) or (0, −f).
- The Heaviside step function can be represented as .
- The Dirac delta "function" is represented by . This is really a restatement of Cauchy's integral formula. To verify it one can calculate the integration of f just below the real line, and subtract integration of g just above the real line - both from left to right. Note that the hyperfunction can be non-trivial, even if the components are analytic continuation of the same function. Also this can be easily checked by differentiating the Heaviside function.
- If g is a continuous function (or more generally a distribution) on the real line with support contained in a bounded interval I, then g corresponds to the hyperfunction (f, −f), where f is a holomorphic function on the complement of I defined by
- This function f jumps in value by g(x) when crossing the real axis at the point x. The formula for f follows from the previous example by writing g as the convolution of itself with the Dirac delta function.
- If f is any function that is holomorphic everywhere except for an essential singularity at 0 (for example, e1/z), then (f, −f) is a hyperfunction with support 0 that is not a distribution. If f has a pole of finite order at 0 then (f, −f) is a distribution, so when f has an essential singularity then (f,−f) looks like a "distribution of infinite order" at 0. (Note that distributions always have finite order at any point.)
See also
References
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- 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.
- 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.