1,747 research outputs found
Dynamics of Individual Specialization and Global Diversification in Communities
We discuss a model of an economic community consisting of interacting
agents. The state of each agent at any time is characterized, in general, by a
mixed strategy profile drawn from a space of pure strategies. The community
evolves as agents update their strategy profiles in response to payoffs
received from other agents. The evolution equation is a generalization of the
replicator equation. We argue that when is sufficiently large and the
payoff matrix elements satisfy suitable inequalities, the community evolves to
retain the full diversity of available strategies even as individual agents
specialize to pure strategies.Comment: 13 pages, Late
Wavelength exponent for haze scattering in the tropics as determined by photoelectric photometers
Sun photometers using narrow-band interference filters, photoelectric sensors and solid-state operational amplifiers were constructed and intensive measurements of the haze extinction co-efficients at 0.40 and 0.60 μm wavelengths made at Poona (Lat. 18° N) over a one-year period. The most significant result obtained is that the wavelength exponent for the haze scattering as calculated from 520 pairs of simultaneous observations shows a median value of 0.5 and a mode of about 0.8. These are substantially lower than corresponding values found in the case of middle latitude stations. In general, the exponent is correlated positively with the turbidity itself in the case of wet haze, and under conditions of very clear and dry air it assumes near zero values. A marked diurnal variation in the value of the exponent occurs during the regimes of tropical continental air. The consequences of the prevailing lower values of α in relation to determination of the Ångström turbidity coefficient β in the tropics are briefly discussed
A new method for the determination of atmospheric turbidity
Atmospheric turbidity is usually measured using either a pyrheliometer fitted with a red RG630 filter or a Volz sun photometer, the turbidity coefficients so determined being designated as β and B, respectively. Both techniques are subject to error, the former in underestimating high turbidities and the latter in giving rise to errors at low turbidities. The present paper describes a new, simpler and less expensive method of evaluating β from measurements of direct and diffuse solar radiation, made as a routine at principal radiation stations. Using a theoretical model for determining the attenuation of solar radiation due to absorption and scattering by water vapour and other gases, dust and aerosols in the atmosphere, an expression for the ratio of diffuse to direct solar radiation D/IH is derived as a function of β. Then, from the hourly mean values of global and diffuse solar radiation routinely recorded at principal radiation stations, D/IH is calculated. β can now be readily evaluated using a special nomogram based on the formula relating β to D/IH. The values of β derived for Indian stations using the above technique show remarkable internal consistency and stability, proving its utility and reliabilit
Denumerable-Armed Bandits
This paper studies the class of denumerable-armed (i.e. finite- or countably infinitearmed)
bandit problems with independent arms and geometric discounting over an
infinite horizon, in which each arm generates rewards according to one of a finite number
of distributions, or "types." The number of types in the support of an arm, as also the
types themselves, are allowed to vary across the arms. We derive certain continuity and
curvature properties of the dynamic allocation (or Gittins) index of Gittins and Jones
(1974), and provide necessary and sufficient conditions under which the Gittins-Jones
result identifying all optimal strategies for finite-armed bandits may be extended to
infinite-armed bandits. We then establish our central result: at each point in time, the
arm selected by an optimal strategy will, with strictly positive probability, remain an
optimal selection forever. More specifically, for every such arm, there exists (at least) one
type of that arm such that, when conditioned on that type being the arm's "true" type,
the arm will survive forever and continuously with nonzero probability. When the reward
distributions of an arm satisfy the monotone likelihood ratio property (MLRP), the
survival prospects of an arm improve when conditioned on types generating higher
expected rewards; however, we show how this need not be the case in the absence of
MLRP. Implications of these results are derived for the theories of job search and
matching, as well as other applications of the bandit paradigm
Switching Costs and the Gittins Index
The Theorem of Gittins and Jones (1974) is, perhaps, the single most powerful result
in the literature on Bandit problems. This result establishes that in independent-armed
Bandit problems with geometric discounting over an infinite horizon, all optimal strategies
may be obtained by solving a family of simple optimal stopping problems that
associate with each arm an index known as the dynamic allocation index or, more
popularly, as the Gittins index. Importantly, the Gittins index of an arm depends solely
on the characteristics of that arm and the rate of discounting, and is otherwise
completely independent of the problem under consideration. These features simplify
significantly the task of characterizing optimal strategies in this class of problems
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