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[[File:Cassini projection SW.jpg|thumb|Cassini projection of the world]]
{{infobox equilibrium|
[[File:Cassini projection squashed SW.JPG|thumb|Cassini projection of the world modeled as a highly oblated ellipsoid with flattening 1:2 (= eccentricy √3/2)]]
name=Quantal response equilibrium|
The '''Cassini projection''' is a [[map projection]] described by [[César-François Cassini de Thury]] in 1745.<ref>''Flattening the Earth: Two Thousand Years of Map Projections'', John P. Snyder, 1993, pp. 74–76, ISBN 0-226-76747-7.</ref> It is the [[transverse aspect]] of the [[equirectangular projection]], in that the globe is first rotated so the central meridian becomes the "equator", and then the normal equirectangular projection is applied. Considering the earth as a sphere, the projection is composed of these operations:
subsetof = [[Bayesian game|Bayes Nash equilibrium]]|
supersetof = [[Nash equilibrium]], [[Logit equilibrium]]|
discoverer = [[Richard McKelvey]] and [[Thomas Palfrey]]|
usedfor = [[Non-cooperative game]]s|
example = [[Traveler's dilemma]]}}


:<math>x = \arcsin(\cos(\phi)\sin(\lambda))\,</math>
'''Quantal response equilibrium''' ('''QRE''') is a [[solution concept]] in [[game theory]]. First introduced by [[Richard McKelvey]] and [[Thomas Palfrey]], it provides an equilibrium notion with [[bounded rationality]]. QRE is not an equilibrium refinement, and it can give significantly different results from [[Nash equilibrium]]. QRE is only defined for games with discrete strategies, although there are continuous-strategy analogues.


:<math>y = \arctan\left(\frac{\tan(\phi)}{\cos(\lambda)}\right)</math>
In a quantal response equilibrium, players are assumed to make errors in choosing which pure strategy to play. The probability of any particular strategy being chosen is positively related to the payoff from that strategy. In other words, very costly errors are unlikely.


where <math>\lambda</math> is the longitude from the central meridian and <math>\phi</math> is the latitude. When programming these equations, the [[inverse tangent]] function used is actually the [[atan2]] function, with the first argument <math>\sin(\phi)</math> and the second <math>\cos(\phi)\cos(\lambda)</math>.
The equilibrium arises from the realization of beliefs. A player's payoffs are computed based on beliefs about other players' probability distribution over strategies. In equilibrium, a player's beliefs are correct.


In practice, the projection has always been applied to models of the earth as an [[Reference ellipsoid|ellipsoid]], which greatly complicates the mathematical development but is suitable for surveying. Nevertheless the use of the Cassini projection has largely been superseded by the [[Transverse Mercator]] projection, at least with central mapping agencies.
== Application to data ==


==Distortions==
When analyzing data from the play of actual games (particularly from [[Experimental economics|laboratory experiments]]), Nash equilibrium can be unforgiving. Any non-equilibrium move can appear equally "wrong", but realistically should not be used to reject a theory. QRE allows every strategy to be played with non-zero probability, and so any data is possible (though not necessarily reasonable).
Areas along the central meridian, and at right angles to it, are not distorted. Elsewhere, the distortion is largely in a north-south direction, and varies by the square of the distance from the central meridian. As such, the greater the longitudinal extent of the area, the worse the distortion becomes.


Due to this, the Cassini projection works best on long, narrow areas, and worst on wide areas.
== Logit equilibrium ==


==References==
By far the most common specification for QRE is '''logit equilibrium''' ('''LQRE'''). In a logit equilibrium, player's strategies are chosen according to the probability distribution:
{{reflist}}
 
<math>P_{ij} = \frac{\exp(\lambda EU_{ij}(P_{-i}))}{\sum_k{\exp(\lambda EU_{ik}(P_{-i}))}}</math>
 
<math>P_{ij}</math> is the probability of player i choosing strategy j.
<math>EU_{ij}(P_{-i}))</math> is the expected utility to player i of choosing strategy j given other players are playing according to the probability distribution <math>P_{-i}</math>.
 
Of particular interest in the logit model is the non-negative parameter λ (sometimes written as 1/μ). λ can be thought of as the rationality parameter. As λ→0, players become "completely irrational", and play each strategy with equal probability. As λ→∞, players become "perfectly rational", and play approaches a Nash equilibrium.
 
== For dynamic games ==
 
For dynamic ([[extensive form game|extensive form]]) games, McKelvey and Palfrey defined '''agent quantal response equilibrium''' ('''AQRE'''). AQRE is somewhat analogous to [[subgame perfection]]. In an AQRE, each player plays with some error as in QRE. At a given decision node, the player determines the expected payoff of each action by treating their future self as an independent player with a known probability distribution over actions.
 
As in QRE, in a AQRE every strategy is used with nonzero probability. This provides an additional advantage of AQRE over perfectly rational solution concepts. Since every path is followed with some probability, there is no concern about defining beliefs "off the equilibrium path".
 
== Critiques ==
=== Free parameter ===
LQRE has the free parameter λ. As λ→∞, LQRE→Nash equilibrium, so LQRE will always be at least as good a fit as Nash equilibrium. Changes in the parameter can result in large changes to equilibrium behavior.


==External links==
However, the theory is incomplete without describing where λ comes from. Estimates of λ from experiments can vary significantly. Sometimes this variance seems to be a result of individual characteristics (for instance, λ sometimes increases with learning). Other times it appears that λ varies from game to game.
* [http://www.radicalcartography.net/?projectionref Table of examples and properties of all common projections], from radicalcartography.net
* [http://webarchive.nationalarchives.gov.uk/20100203170955/ordnancesurvey.co.uk/oswebsite/freefun/geofacts/geo1164.html Ordnance Survey GeoFacts on the Cassini Projection]


{{Map Projections}}
==References==
* {{Citation
  | last1 = McKelvey | first1 = Richard
  | author1-link = Richard McKelvey
  | last2 = Palfrey | first2 = Thomas
  | author2-link = Thomas Palfrey
  | title = Quantal Response Equilibria for Normal Form Games
  | journal = Games and Economic Behavior
  | volume = 10
  | pages = 6–38
  | year = 1995
  | doi = 10.1006/game.1995.1023 }}
* {{Citation
  | last1 = McKelvey | first1 = Richard
  | author1-link = Richard McKelvey
  | last2 = Palfrey | first2 = Thomas
  | author2-link = Thomas Palfrey
  | title = Quantal Response Equilibria for Extensive Form Games
  | journal = Experimental Economics
  | volume = 1
  | pages = 9–41
  | year = 1998
  | doi = 10.1007/BF01426213 }}


{{DEFAULTSORT:Cassini Projection}}
{{Game theory}}
[[Category:Cartographic projections]]
{{gametheory-stub}}


{{Cartography-stub}}
[[Category:Game theory]]

Revision as of 16:26, 15 August 2014

Template:Infobox equilibrium

Quantal response equilibrium (QRE) is a solution concept in game theory. First introduced by Richard McKelvey and Thomas Palfrey, it provides an equilibrium notion with bounded rationality. QRE is not an equilibrium refinement, and it can give significantly different results from Nash equilibrium. QRE is only defined for games with discrete strategies, although there are continuous-strategy analogues.

In a quantal response equilibrium, players are assumed to make errors in choosing which pure strategy to play. The probability of any particular strategy being chosen is positively related to the payoff from that strategy. In other words, very costly errors are unlikely.

The equilibrium arises from the realization of beliefs. A player's payoffs are computed based on beliefs about other players' probability distribution over strategies. In equilibrium, a player's beliefs are correct.

Application to data

When analyzing data from the play of actual games (particularly from laboratory experiments), Nash equilibrium can be unforgiving. Any non-equilibrium move can appear equally "wrong", but realistically should not be used to reject a theory. QRE allows every strategy to be played with non-zero probability, and so any data is possible (though not necessarily reasonable).

Logit equilibrium

By far the most common specification for QRE is logit equilibrium (LQRE). In a logit equilibrium, player's strategies are chosen according to the probability distribution:

is the probability of player i choosing strategy j. is the expected utility to player i of choosing strategy j given other players are playing according to the probability distribution .

Of particular interest in the logit model is the non-negative parameter λ (sometimes written as 1/μ). λ can be thought of as the rationality parameter. As λ→0, players become "completely irrational", and play each strategy with equal probability. As λ→∞, players become "perfectly rational", and play approaches a Nash equilibrium.

For dynamic games

For dynamic (extensive form) games, McKelvey and Palfrey defined agent quantal response equilibrium (AQRE). AQRE is somewhat analogous to subgame perfection. In an AQRE, each player plays with some error as in QRE. At a given decision node, the player determines the expected payoff of each action by treating their future self as an independent player with a known probability distribution over actions.

As in QRE, in a AQRE every strategy is used with nonzero probability. This provides an additional advantage of AQRE over perfectly rational solution concepts. Since every path is followed with some probability, there is no concern about defining beliefs "off the equilibrium path".

Critiques

Free parameter

LQRE has the free parameter λ. As λ→∞, LQRE→Nash equilibrium, so LQRE will always be at least as good a fit as Nash equilibrium. Changes in the parameter can result in large changes to equilibrium behavior.

However, the theory is incomplete without describing where λ comes from. Estimates of λ from experiments can vary significantly. Sometimes this variance seems to be a result of individual characteristics (for instance, λ sometimes increases with learning). Other times it appears that λ varies from game to game.

References

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    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.

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Earlier than you decide whether stainless steel cookware is worth buying, lets first discuss what stainless steel cookware is. Chrome steel is manufactured from an alloy, or a mix of metals. Mostly, basic iron with chromium, nickel or another minor metals. The chromium supplies rust safety and gives your cookware durability. The nickel supplies rust safety as effectively, and adds a elegant look. Most properly made chrome steel cookware has copper or aluminum added to the bottom of the pan or pot. That is performed to increases the ability of the pot or pan to conduct heat.
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You can find magnetic chrome steel in the layer on the outside of some quality pieces of stainless steel. This is to make it suitable with induction stovetops, which involve the use of a quickly charging electromagnetic area to warmth cookware. Excessive-quality stainless-steel, like All-Clad , makes use of three layers of steel—the austenite layer of metal on the within, ferrite steel on the skin, and a layer of aluminum sandwiched between the 2 for optimum warmth conductivity (metal alone does not conduct heat evenly). Lesser-quality stainless steel is usually just one layer of austenitic chrome steel.
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The enamel over steel technique creates a bit that has the warmth distribution of carbon steel and a non-reactive, low-stick floor. Such pots are much lighter than most different pots of similar measurement, are cheaper to make than stainless-steel pots, and don't have the rust and reactivity problems with cast iron or carbon steel. citation wanted Enamel over metal is ideal for big stockpots and for other giant pans used largely for water-based cooking. Because of its mild weight and simple cleanup, enamel over metal is also common for cookware used while camping. For more about stainless steel cookware reviews look at our web site. Clad aluminium or copper edit
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