Papers by Evangelos Magirou
We present an elementary analysis of the dynamical aspects of the GDP / government surplus multip... more We present an elementary analysis of the dynamical aspects of the GDP / government surplus multiplier with relevance to the assessment of a country's debt repayment policy. We show the (at first) counter intuitive result that in order to reduce the Debt/GDP ratio, countries with high Debt to GDP should go into further debt, as long as the Debt to GDP ratio is roughly greater than the inverse of the multiplier. Thus small values of the multiplier make further debt undesirable, and conversely.
We analyze an optimal control version of a simple SIR epidemiology model that includes a partiall... more We analyze an optimal control version of a simple SIR epidemiology model that includes a partially specified vaccination policy and takes into account fatigue from protracted application of social distancing measures. The model assumes demographic (age related) categories, and is otherwise homogeneous. Maximum capacity for vaccination is exogenous and the authorities select its allocation to the categories. They can also adopt measures to uniformly diminish the contact rate between infected and susceptible individuals at an economic cost. Total or partial immunity is modeled, while the contact rate is allowed to exhibit seasonality. We apply optimal control methods to minimize a cost index while guaranteeing that health system capacity is not exceeded. A reasonable parameter selection leads to policies specifying that vaccination priority should be given to the category with a higher demand for the limited health care resources regardless of cost variations among categories. Vaccina...
International Conference on Email and Anti-Spam, 2005
International Conference on Email and Anti-Spam, 2007
Annals of Mathematics and Artificial Intelligence, 1997
Extensions in prerequisite‐free, disjunction‐free default theories have been shown to be in direc... more Extensions in prerequisite‐free, disjunction‐free default theories have been shown to be in direct correspondence with kernels of directed graphs; hence default theories without odd cycles always have a “standard” kind of an extension. We show that, although all “standard” extensions can be enumerated explicitly, several other problems remain intractable for such theories: Telling whether a non‐standard extension exists, enumerating all
The purpose of this paper is to investigate the problem of modal split for passengers and vehicle... more The purpose of this paper is to investigate the problem of modal split for passengers and vehicles in a specific context, that of the Greek coastal shipping system. The transport modes considered are conventional passenger/car ferries (P/C vessels), fast (30-50 knot) vessels, and air transport. For a variety of reasons, monumental changes are about to take place within this system over the next decade. These center primarily on the deregulation of the market that is a result of the European Union integration, and on the introduction of vessels capable of carrying passengers and cars at high speeds. By EU directive, the Greek coastal market shall be fully deregulated by the year 2004. This means that owners would be able to set up routes with minimal governmental interference. The question is of course how passenger demand will evolve within such a new environment, and how the various competing modes of transport will fare. This paper is an attempt to systematically analyze scenarios...
INFORMS Transactions on Education, 2008
We discuss how the interaction between spam senders and e-mail users can be modelled as a two-pla... more We discuss how the interaction between spam senders and e-mail users can be modelled as a two-player adversary game. We show how the resulting model can be used to predict the strategies that the two opponent communities will eventually adopt, and how it can be employed to tune anti-spam filters. 1
We show how a game-theoretic model of spam e-mailing, which we had introduced in previous work, c... more We show how a game-theoretic model of spam e-mailing, which we had introduced in previous work, can be extended to include the possibility of employing Human Interactive Proofs (hips) in conjunction with filters that classify incoming messages as legitimate or spam. Using our extended model, we show that making hips widely available to e-mail users will reduce the volume of spam on the Internet and increase the benefit that legitimate users obtain from e-mail. 1.
arXiv: Populations and Evolution, 2020
We analyze an optimal control version of a simple SIRS epidemiology model. The policy maker can a... more We analyze an optimal control version of a simple SIRS epidemiology model. The policy maker can adopt policies to diminish the contact rate between infected and susceptible individuals, at a specific economic cost. The arrival of a vaccine will immediately end the epidemic. Total or partial immunity is modeled, while the contact rate can exhibit a (user specified) seasonality. The problem is solved in a spreadsheet environment. A reasonable parameter selection leads to optimal policies which are similar to those followed by different countries. A mild response relying on eventually reaching a high immunity level is optimal if ample health facilities are available. On the other hand limited health care facilities lead to strict lock downs while moderate ones allow a flattening of the curve approach.
We discuss how the interaction between spam senders and e-mail users can be modelled as a two-pla... more We discuss how the interaction between spam senders and e-mail users can be modelled as a two-player adversary game. We show how the resulting model can be used to predict the strategies that the two opponent communities will eventually adopt, and how it can be employed to tune anti-spam filters.
arXiv: Populations and Evolution, 2021
We analyze an optimal control version of a simple SIR epidemiology model that includes a partiall... more We analyze an optimal control version of a simple SIR epidemiology model that includes a partially specified vaccination policy and takes into account fatigue from protracted application of social distancing measures. The model assumes demographic (age related) categories, and is otherwise homogeneous. Maximum capacity for vaccination is exogenous and the authorities select its allocation to the categories. They can also adopt measures to uniformly diminish the contact rate between infected and susceptible individuals at an economic cost. Total or partial immunity is modeled, while the contact rate is allowed to exhibit seasonality. We apply optimal control methods to minimize a cost index while guaranteeing that health system capacity is not exceeded. A reasonable parameter selection leads to policies specifying that vaccination priority should be given to the category with a higher demand for the limited health care resources regardless of cost variations among categories. Vaccina...
arXiv: General Finance, 2013
We present an elementary analysis of the dynamical aspects of the GDP / government surplus multip... more We present an elementary analysis of the dynamical aspects of the GDP / government surplus multiplier with relevance to the assessment of a country's debt repayment policy. We show the (at first) counter intuitive result that in order to reduce the Debt/GDP ratio, countries with high Debt to GDP should go into further debt, as long as the Debt to GDP ratio is roughly greater than the inverse of the multiplier. Thus small values of the multiplier make further debt undesirable, and conversely.
We show how a game-theoretic model of spam e-mailing, which we had introduced in previous work, c... more We show how a game-theoretic model of spam e-mailing, which we had introduced in previous work, can be extended to include the possibility of employing Human Interactive Proofs (hips) in conjunction with filters that classify incoming messages as legitimate or spam. Using our extended model, we show that making hips widely available to e-mail users will reduce the volume of spam on the Internet and increase the benefit that legitimate users obtain from e-mail.
We present at the conceptual level an alternative method for pricing American options. Most compu... more We present at the conceptual level an alternative method for pricing American options. Most computational procedures in the literature rely on backward induction dynamic programming of the problem's discretization. We show how a policy iteration method can be directly applied to the continuous time version of the problem. The concept of improving the exercise boundary is presented, elementary analysis is given and a numerical example is presented.
Journal of Computational and Applied Mathematics
Resources and Energy
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Papers by Evangelos Magirou