In mathematics and classical mechanics, canonical coordinates are a particular set of coordinates on the phase space, or equivalently, on the cotangent manifold of a manifold. Canonical coordinates arise naturally in physics in the study of Hamiltonian mechanics. As Hamiltonian mechanics is generalized by symplectic geometry and canonical transformations are generalized by contact transformations, so the 19th century definition of canonical coordinates in classical mechanics may be generalized to a more abstract 20th century definition in terms of cotangent bundles.
This article defines the canonical coordinates as they appear in classical mechanics. A closely related concept also appears in quantum mechanics; see the Stone-von Neumann theorem and canonical commutation relations for details.
Definition, in classical mechanics
In classical mechanics, canonical coordinates are the coordinates <math>q_i\,</math> and <math>p_i\,</math> in phase space that are used in the Hamiltonian formalism. The canonical coordinates satisfy the fundamental Poisson bracket relations:
- <math>\{q_i, q_j\} = 0 \qquad \{p_i, p_j\} = 0 \qquad \{q_i, p_j\} = \delta_{ij}</math>
Canonical coordinates can be obtained from the generalized coordinates of the Lagrangian formalism by a Legendre transformation, or from another set of canonical coordinates by a canonical transformation.
Definition, on cotangent bundles
Canonical coordinates are defined as a special set of coordinates on the cotangent bundle of a manifold. They are usually written as a set of <math>(q^i,p_j)</math> or <math>(x^i,p_j)</math> with the x ’s or q ’s denoting the coordinates on the underlying manifold and the p ’s denoting the conjugate momentum, which are 1-forms in the cotangent bundle at point q in the manifold.
A common definition of canonical coordinates is any set of coordinates on the cotangent bundle that allow the canonical one form to be written in the form
- <math>\sum_i p_i\,\mathrm{d}q^i</math>
up to a total differential. A change of coordinates that preserves this form is a canonical transformation; these are a special case of a symplectomorphism, which are essentially a change of coordinates on a symplectic manifold.
In the following exposition, we assume that the manifolds are real manifolds, so that cotangent vectors acting on tangent vectors produce real numbers.
Formal development
Given a manifold Q, a vector field X on Q (or equivalently, a section of the tangent bundle TQ) can be thought of as a function acting on the cotangent bundle, by the duality between the tangent and cotangent spaces. That is, define a function
- <math>P_X:T^*Q\to \mathbb{R}</math>
such that
- <math>P_X(q,p)=p(X_q)</math>
holds for all cotangent vectors p in <math>T_q^*Q</math>. Here, <math>X_q</math> is a vector in <math>T_qQ</math>, the tangent space to the manifold Q at point q. The function <math>P_X</math> is called the momentum function corresponding to X.
In local coordinates, the vector field X at point q may be written as
- <math>X_q=\sum_i X^i(q) \frac{\partial}{\partial q^i}</math>
where the <math>\partial /\partial q^i</math> are the coordinate frame on TQ. The conjugate momentum then has the expression
- <math>P_X(q,p)=\sum_i X^i(q) \;p_i</math>
where the <math>p_i</math> are defined as the momentum functions corresponding to the vectors <math>\partial /\partial q^i</math>:
- <math>p_i = P_{\partial /\partial q^i}</math>
The <math>q^i</math> together with the <math>p_j</math> together form a coordinate system on the cotangent bundle <math>T^*Q</math>; these coordinates are called the canonical coordinates.
Generalized coordinates
In Lagrangian mechanics, a different set of coordinates are used, called the generalized coordinates. These are commonly denoted as <math>(q^i,\dot{q}^i)</math> with <math>q^i</math> called the generalized position and <math>\dot{q}^i</math> the generalized velocity. When a Hamiltonian is defined on the cotangent bundle, then the generalized coordinates are related to the canonical coordinates by means of the Hamilton–Jacobi equations.
See also
- symplectic manifold
- symplectic vector field
- symplectomorphism
Monday, February 25th, 2008
Gross Output is an economic concept used in national accounts such as the United Nations System of National Accounts (UNSNA) and the US National Income and Product Accounts (NIPA). It is equal to the value of net output or GDP (also known as gross value added) plus intermediate consumption.
Gross Output represents, roughly speaking, the total value of sales by producing enterprises in an accounting period (e.g. a quarter or a year), before subtracting the value of intermediate goods used up in production. This description is not quite accurate though, among other things because flows relating to government services and households are also included.
To obtain a measure of gross value added or Net output, the value of intermediate goods and services must be subtracted from Gross Output. Net value added is obtained by additionally subtracting consumption of fixed capital (depreciation).
The statistical definition of Gross Output is dependent upon the definition of production applied. Typically some economic flows and activities are excluded from coverage in calculating the value of Gross Output, on the ground that they are unrelated to production in the domestic economy. These include foreign transactions, property income, transfers, and various government disbursements, unpaid housework and voluntary work. On the other hand, items are included which some economists would regard as spurious, such as the imputed rental value of owner-occupied housing (this is the average rents, at market rates, which owners of residential housing would receive if they rented out the housing they occupy).
See also
- GDP
- Intermediate consumption
- Net output
- United Nations System of National Accounts (UNSNA)
- National accounts
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Monday, February 25th, 2008
Sometimes
a Great Notion may refer to:
- Sometimes a Great Notion (novel)
- Sometimes a Great Notion (1971 film)
- JEAN-PIERRE BELNA. La Notion de Nombre chez Dedekind, Cantor book is of great value and interest and that, on the whole, it exemplifies. philosophy practiced at its best. JEAN-PIERRE BELNA. La Notion de Nombre chez
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Monday, February 25th, 2008
NCST can refer to:
- National Centre for Software Technology in India, now Centre for Development of Advanced Computing (C-DAC)
- National College of Science and Technology in Philippines.
- North Carolina State University in United States
- ITS - Public Computing Centers The following public computer centers are open for student use and they have classrooms that can be reserved for hands on instruction.
- School of Computing and Information Sciences @ FIU Apr. 5, 2007 at 2pm in ECS 243 by Dr. Jason Liu, Assistant Professor, Mathematical & Computer Sciences, Colorado School of Mines
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Sunday, February 24th, 2008
The Konrad Adenauer is a German aircraft used by the head-of-government for official travel and diplomatic business.
- Nuclear Dispute with Iran: Merkel Pushes Russian Diplomatic Role, by Ralf Beste, Ralf Neukirch and Gabor Steingart, from Der Spiegel, January 23, 2006
See also
- Air Force One, the analogous plane used by the United States President.
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Sunday, February 24th, 2008
In economics, cardinal utility is a theory of utility under which the utility (roughly, satisfaction) gained from a particular good or service can be measured and that the magnitude of the measurement is meaningful. Under cardinal utility theory, the util is a unit of measurement much like the metre or second. A util has a fixed size, making comparisons based on ratios of utils possible. Perhaps more importantly, however, cardinal utility allows for comparisons of utility across persons—if a particular good gives Alice 200 utils but Bob only gets 100 utils from the same good, the good is said to give Alice twice as much utility as it does Bob.
This sort of comparison is of great theoretical value in social planning and ethics. Under the framework of utilitarianism, actions (including production of goods and provision of services) are judged by their contributions to overall happiness. Cardinal utility provides a way of judging the “greatest good to the greatest number”. An act that reduces one person’s utility by 75 utils while increasing two others’ by 50 utils each has increased overall utility by 25 utils and is thus a positive contribution; one that costs the first person 125 utils while giving the same 50 each to two other people has resulted in a net loss of 25 utils.
This ability to neatly compare utilities in theory runs into problems in practice. There are major difficulties in measuring utility, which is inherently subjective. Unlike with distance or time, one cannot simply use a ruler or stopwatch to measure satisfaction. It is not simple to definitively say whether a good is worth 50, 75, or 125 utils to a person, or even if it is worth the same number of utils to two different people. These problems have resulted in a shift in microeconomic theory towards ranked preferences or ordinal utility, in which a good with a higher utility is preferred to one with lower utility but the magnitude of the difference has no meaning.
There remain economists who believe that utility can be measured. These measures are not perfect but can act as a proxy for the utility. Lancaster’s characteristics approach to consumer demand illustrates this point.
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Sunday, February 24th, 2008
A Community of interest is a community of people who share a common interest or passion, such as rugby fans on Rugby365.com, or music lovers on MP3.com. These people exchange ideas and thoughts about the given passion, but may know (or care) little about each other outside of this area. Participation in a community of interest can be compelling, entertaining and create a ‘sticky’ community where people return frequently and remain for extended periods. They sometimes cannot be easily defined by a particular geographical area.
Related to
- Communities of Action
- Communities of Circumstance
- Communities of Position
- Communities of Practice
- Communities of Purpose
- Community of inquiry
See also
External links
- External and shareable artifacts as opportunities for social creativity in communities of interest
- Communities of Interest: Learning through the Interaction of Multiple Knowledge Systems
- Bradford (UK) Communities of Interest site Deals with Communities of Interest within Bradford.
Sunday, February 24th, 2008
In mathematics, the prime decomposition theorem for 3-manifolds states that every compact, orientable 3-manifold is the connected sum of a unique (up to homeomorphism) collection of prime 3-manifolds.
The manifold is prime if it can not be presented as a connected sum in a non-trivial way, where the trivial way is
- <math>P=P\#S^3.</math>
If <math>P</math> is a prime 3-manifold then either it is
<math>S^2\times S^1</math> or the non-orientable <math>S^2</math> bundle over <math>S^1</math>,
or any embedded 2-sphere in <math>P</math> bounds a ball, i.e. is irreducible. So the theorem can be restated to say that there is a unique connected sum decomposition into irreducible 3-manifolds and <math>S^2 \times S^1</math>’s.
The prime decomposition holds also for non-orientable 3-manifolds, but the uniqueness statement must be modified slightly: every compact, non-orientable 3-manifold is a connected sum of irreducible 3-manifolds and non-orientable <math>S^2</math> bundles over <math>S^1</math>. This sum is unique as long as we specify that each summand is either irreducible or a non-orientable <math>S^2</math> bundle over <math>S^1</math>.
The proof is based on normal surface techniques originated by Hellmuth Kneser. Existence was proven by Kneser, but the exact formulation and proof of the uniqueness was done more than 30 years later by John Milnor.
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Sunday, February 24th, 2008
Oldfieldia is a plant genus under the family Picrodendraceae, the only of its subtribe (Paiveusinae).
The genus includes Cecchia Chiov. and Paivaeusa Welw..
Sunday, February 24th, 2008
South Central Arkansas Electric Cooperative is a non-profit rural electric utility cooperative headquartered in Arkadelphia, Arkansas. The Cooperative was organized in 1940.
The Cooperative serves portions of eight counties in the state of Arkansas, in a territory generally west and southwest of Arkadelphia.
As of September 2005, the Cooperative had more than 1,770 miles of distribution lines, 9 substations and services 7,300 member accounts.
External links
- South Central Arkansas Electric Cooperative
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Sunday, February 24th, 2008
Leased Access airtime is airtime that the Federal Communications Commission mandates must be provided by cable operators (i.e. companies like Comcast and Time Warner Cable) for use by cable programmers, i.e., those who make cable programming, who are not owned by the operators. The prices for leased access airtime are subject to a maximum set by an FCC formula and therefore in theory cannot be manipulated by cable companies. Cable companies, however, can “manipulate” prices through lobbying the FCC. Indeed, in 1997, the FCC set maximum prices based on an “average implicit fee” formula which set the prices considered by cable programmers to be very high. Lower prices would likely encourage increased usage of leased access by independent programmers. Leased access airtime may be purchased by individuals or groups with E&O insurance for the purposes of airing television content, usually locally produced.
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Sunday, February 24th, 2008
Year 1733 (MDCCXXXIII) was a common year starting on Thursday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 11-day slower Julian calendar).
Events of
January - June
- February 12 - British colonist James Oglethorpe founds Savannah, Georgia.
- April - Royal Colony of North Carolina Commissioners John Watson, Joshua Grainger, Michael Higgins and James Wimble plan the town of New Carthage (which would eventually become Wilmington, North Carolina on the east side of the Cape Fear River).
- May 29 - Right of Canadians to keep Indian slaves upheld at Quebec.
July - December
- July 30 - First Freemasons lodge opened in what will become the United States of America.
Births
- March 13 - Joseph Priestley, English scientist and minister (died 1804)
- May 4 - Jean-Charles de Borda, French mathematician, physicist, political scientist, and sailor (died 1799)
- July 27 - Jeremiah Dixon, English surveyor and astronomer (died 1779)
- September 18 - George Read, American lawyer and signer of the Declaration of Independence (died 1798)
- October 14 - François Sebastien Charles Joseph de Croix, Count of Clerfayt, Austrian field marshal (died 1798)
- November 16 - Siraj ud-Daulah, the last independent ruler of Bengal of undivided India (died 1757)
- See also .
Deaths
- January 25 - Gilbert Heathcote, Mayor of London (born 1652)
- February 1 - King August II of Poland (born 1670)
- March 4 - Claude de Forbin, French naval commander (born 1656)
- April 19 - Elizabeth Villiers, mistress of William III of England (born 1657)
- May 10 - Barton Booth, English actor (born 1681)
- May 18 - Georg Böhm, German organist (born 1661)
- August 16 - Matthew Tindal, English deist (born 1657)
- June 23 - Johann Jakob Scheuchzer, Swiss scholar (born 1672)
- September 12 - François Couperin, French composer (born 1668)
- October 25 - Giovanni Gerolamo Saccheri, Italian mathematician (born 1667)
- October 31 - Eberhard Ludwig, Duke of Württemberg, (born 1676)
- See also .
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Sunday, February 24th, 2008
In economics, marginal concepts refer to the effect of producing or consuming one more of a good, i.e. at the edge, or margin, of the total produced/consumed.
For example, marginal cost refers to the cost of producing one more unit of some good. In general this will be lower than the average cost because the average cost includes fixed costs. (See economies of scale). Marginal benefit is the extra utility accrued from one additional unit of a good.
Similarly marginal utility is the additional utility (satisfaction or benefit) that a consumer derives from an additional unit of a commodity or service. It is assumed that marginal utility generally falls as consumption increases, so that one’s 10th doughnut in a day is less satisfying than the first or second.
Other marginal concepts include:
- marginal tax rate
- marginal propensity to save and consume
- marginal rate of substitution
The related concept of elasticity is the ratio of the incremental percentage change in one variable with respect to an incremental percentage change in another variable.
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Sunday, February 24th, 2008
In microeconomics, the expenditure minimization problem is the dual problem to the utility maximization problem: “how much money do I need to be happy?”. This question comes in two parts. Given a consumer’s utility function, prices, and a utility target,
- how much money would the consumer need? This is answered by the expenditure function.
- what could the consumer buy to meet this utility target while minimizing expenditure? This is answered by the Hicksian demand correspondence.
Expenditure function
Formally, the expenditure function is defined as follows. Suppose the consumer has a utility function <math>u</math> defined on <math>L</math> commodities. Then the consumer’s expenditure function gives the amount of money required to buy a package of commodities at given prices <math>p</math> that give utility greater than <math>u^*</math>,
- <math>e(p, u^*) = \min_{x \in \geq{u^*}} p \cdot x</math>
where
- <math>\geq{u^*} = \{x \in \textbf R^L_+ : u(x) \geq u^*\}</math>
is the set of all packages that give utility at least as good as <math>u^*</math>.
Hicksian demand correspondence
Secondly, the Hicksian demand correspondence <math>h(p, u^*)</math> is defined as the cheapest package that gives the desired utility. It can be defined in terms of the expenditure function with the Marshallian demand correspondence