26,014 research outputs found
Environmental Noise Variability in Population Dynamics Matrix Models
The impact of environmental variability on population size growth rate in
dynamic models is a recurrent issue in the theoretical ecology literature. In
the scalar case, R. Lande pointed out that results are ambiguous depending on
whether the noise is added at arithmetic or logarithmic scale, while the matrix
case has been investigated by S. Tuljapurkar. Our contribution consists first
in introducing another notion of variability than the widely used variance or
coefficient of variation, namely the so-called convex orders. Second, in
population dynamics matrix models, we focus on how matrix components depend
functionaly on uncertain environmental factors. In the log-convex case, we show
that, in a sense, environmental variability increases both mean population size
and mean log-population size and makes them more variable. Our main result is
that specific analytical dependence coupled with appropriate notion of
variability lead to wide generic results, valid for all times and not only
asymptotically, and requiring no assumptions of stationarity, of normality, of
independency, etc. Though the approach is different, our conclusions are
consistent with previous results in the literature. However, they make it clear
that the analytical dependence on environmental factors cannot be overlooked
when trying to tackle the influence of variability.Comment: 9 page
Rationally Biased Learning
Are human perception and decision biases grounded in a form of rationality?
You return to your camp after hunting or gathering. You see the grass moving.
You do not know the probability that a snake is in the grass. Should you cross
the grass - at the risk of being bitten by a snake - or make a long, hence
costly, detour? Based on this storyline, we consider a rational decision maker
maximizing expected discounted utility with learning. We show that his optimal
behavior displays three biases: status quo, salience, overestimation of small
probabilities. Biases can be the product of rational behavior
Preferences Yielding the "Precautionary Effect"
Consider an agent taking two successive decisions to maximize his expected
utility under uncertainty. After his first decision, a signal is revealed that
provides information about the state of nature. The observation of the signal
allows the decision-maker to revise his prior and the second decision is taken
accordingly. Assuming that the first decision is a scalar representing
consumption, the \emph{precautionary effect} holds when initial consumption is
less in the prospect of future information than without (no signal).
\citeauthor{Epstein1980:decision} in \citep*{Epstein1980:decision} has provided
the most operative tool to exhibit the precautionary effect. Epstein's Theorem
holds true when the difference of two convex functions is either convex or
concave, which is not a straightforward property, and which is difficult to
connect to the primitives of the economic model. Our main contribution consists
in giving a geometric characterization of when the difference of two convex
functions is convex, then in relating this to the primitive utility model. With
this tool, we are able to study and unite a large body of the literature on the
precautionary effect
Preferences Yielding the ``Precautionary Effect''
Consider an agent taking two successive decisions to maximize his expected utility under uncertainty. After his first decision, a signal is revealed that provides information about the state of nature. The observation of the signal allows the decision-maker to revise his prior and the second decision is taken accordingly. Assuming that the first decision is a scalar representing consumption, the \emph{precautionary effect} holds when initial consumption is less in the prospect of future information than without (no signal). \citeauthor{Epstein1980:decision} in \citep*{Epstein1980:decision} has provided the most operative tool to exhibit the precautionary effect. Epstein's Theorem holds true when the difference of two convex functions is either convex or concave, which is not a straightforward property, and which is difficult to connect to the primitives of the economic model. Our main contribution consists in giving a geometric characterization of when the difference of two convex functions is convex, then in relating this to the primitive utility model. With this tool, we are able to study and unite a large body of the literature on the precautionary effect.value of information; uncertainty; learning; precautionary effect; support function
The role of oblivion, memory size and spatial separation in dynamic language games
In this paper we present some multiagent simulations in which the individuals try to reach a uniform vocabulary to name spatial movements. Each agent has initially a random vocabulary that can be modified by means of interactions with the other agents. As the objective is to name movements, the topic of conversation is chosen by moving. Each agent can remember a finite number of words per movement, with certain strength. We show the importance of the forgetting process and memory size in these simulations, discuss the effect of the number of agents on the time to agree and present a few experiments where the evolution of vocabularies takes place in a divided range.This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project numbers TEL1999-0181, and TIC 2001-0685-C02-01
Event-driven grammars: Relating abstract and concrete levels of visual languages
The final publication is available at Springer via http://dx.doi.org/10.1007/s10270-007-0051-2In this work we introduce event-driven grammars, a kind of graph grammars that are especially suited for visual modelling environments generated by meta-modelling. Rules in these grammars may be triggered by user actions (such as creating, editing or connecting elements) and in their turn may trigger other user-interface events. Their combination with triple graph transformation systems allows constructing and checking the consistency of the abstract syntax graph while the user is building the concrete syntax model, as well as managing the layout of the concrete syntax representation. As an example of these concepts, we show the definition of a modelling environment for UML sequence diagrams. A discussion is also presented of methodological aspects for the generation of environments for visual languages with multiple views, its connection with triple graph grammars, the formalization of the latter in the double pushout approach and its extension with an inheritance concept.This work has been partially sponsored by the Spanish Ministry of Education and Science with projects MOSAIC (TSI2005-08225-C07-06) and MODUWEB (TIN 2006-09678)
The Slavonic tradition of the quaestiones ad antiochum ducem : the conflated nature of Cod. Pragensis Slav. IX F 15
The late fourteenth-century Codex Pragensis slav. IX F 15 is a key witness to the textual tradition of the Slavonic Quaestiones ad Antiochum ducem as it contains an almost complete set of questions-and-answers (133 QA’s). It is argued, however, that this corpus is the result of a conflation of two distinct versions of the Quaestiones, viz. redaction T and version X.
Redaction T, found in five Moscou manuscripts (15th-16th c.), is the result of a revision of the Slavonic Quaestiones based on the consultation of a Greek exemplar: both the structure (viz. the number and sequence of the QA’s) and the textual particulars of the Greek Quaestiones found in Codex Oxoniensis Bodleianus gr. Auct. F.4.07 are shown to be in almost perfect agreement with the Slavonic T-witnesses.
Version X is much more enigmatic; apparently, QA’s from this further unknown text version were introduced in the Prague codex to complement the T-redaction’s corpus of 120 QA’s
Some strategies for the simulation of vocabulary agreement in multi-agent communities
In this paper, we present several experiments of belief propagation in multi-agent communities. Each agent in the simulation has an initial random vocabulary (4 words) corresponding to each possible movement (north, south, east and west). Agents move and communicate the associated word to the surrounding agents, which can be convinced by the 'speaking agent', and change their corresponding word by 'imitation'. Vocabulary uniformity is achieved, but strong interactions and competition can occur between dominant words. Several moving and trusting strategies as well as agent roles are analyzed.This paper has been sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project number TEL1999-0181
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