18,374 research outputs found
Marginal productivity index policies for problems of admission control and routing to parallel queues with delay
In this paper we consider the problem of admission control of Bernoulli arrivals to a
buffer with geometric server, in which the controller’s actions take effect one period
after the actual change in the queue length. An optimal policy in terms of marginal
productivity indices (MPI) is derived for this problem under the following three
performance objectives: (i) minimization of the expected total discounted sum of
holding costs and rejection costs, (ii) minimization of the expected time-average sum of
holding costs and rejection costs, and (iii) maximization of the expected time-average
number of job completions. Our employment of existing theoretical and algorithmic
results on restless bandit indexation together with some new results yields a fast
algorithm that computes the MPI for a queue with a buffer size of I performing only
O(I) arithmetic operations. Such MPI values can be used both to immediately obtain the
optimal thresholds for the admission control problem, and to design an index policy for
the routing problem (with possible admission control) in the multi-queue system. Thus,
this paper further addresses the problem of designing and computing a tractable
heuristic policy for dynamic job admission control and/or routing in a discrete time
Markovian model of parallel loss queues with one-period delayed state observation
and/or action implementation, which comes close to optimizing an infinite-horizon
problem under the above three objectives. Our approach seems to be tractable also for
the analogous problems with larger delays and, more generally, for arbitrary restless
bandits with delays
Analysis of the effect of clock drifts on frequency regulation and power sharing in inverter-based islanded microgrids
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Local hardware clocks in physically distributed computation devices hardly ever agree because clocks drift apart and the drift can be different for each device. This paper analyses the effect that local clock drifts have in the parallel operation of voltage source inverters (VSIs) in islanded microgrids (MG). The state-of-the-art control policies for frequency regulation and active power sharing in VSIs-based MGs are reviewed and selected prototype policies are then re-formulated in terms of clock drifts. Next, steady-state properties for these policies are analyzed. For each of the policies, analytical expressions are developed to provide an exact quantification of the impact that drifts have on frequency and active power equilibrium points. In addition, a closed-loop model that accommodates all the policies is derived, and the stability of the equilibrium points is characterized in terms of the clock drifts. Finally, the implementation of the analyzed policies in a laboratory MG provides experimental results that confirm the theoretical analysis.Peer ReviewedPostprint (author's final draft
Marginal productivity index policies for problems of admission control and routing to parallel queues with delay
In this paper we consider the problem of admission control of Bernoulli arrivals to a buffer with geometric server, in which the controller’s actions take effect one period after the actual change in the queue length. An optimal policy in terms of marginal productivity indices (MPI) is derived for this problem under the following three performance objectives: (i) minimization of the expected total discounted sum of holding costs and rejection costs, (ii) minimization of the expected time-average sum of holding costs and rejection costs, and (iii) maximization of the expected time-average number of job completions. Our employment of existing theoretical and algorithmic results on restless bandit indexation together with some new results yields a fast algorithm that computes the MPI for a queue with a buffer size of I performing only O(I) arithmetic operations. Such MPI values can be used both to immediately obtain the optimal thresholds for the admission control problem, and to design an index policy for the routing problem (with possible admission control) in the multi-queue system. Thus, this paper further addresses the problem of designing and computing a tractable heuristic policy for dynamic job admission control and/or routing in a discrete time Markovian model of parallel loss queues with one-period delayed state observation and/or action implementation, which comes close to optimizing an infinite-horizon problem under the above three objectives. Our approach seems to be tractable also for the analogous problems with larger delays and, more generally, for arbitrary restless bandits with delays.Admission control, Routing, Parallel queues, Delayed information, Delayed action implementation, Index policy, Restless bandits, Marginal productivity index
The Importance of Social and Government Learning in Ex Ante Policy Evaluation
We provide two methodological insights on \emph{ex ante} policy evaluation
for macro models of economic development. First, we show that the problems of
parameter instability and lack of behavioral constancy can be overcome by
considering learning dynamics. Hence, instead of defining social constructs as
fixed exogenous parameters, we represent them through stable functional
relationships such as social norms. Second, we demonstrate how agent computing
can be used for this purpose. By deploying a model of policy prioritization
with endogenous government behavior, we estimate the performance of different
policy regimes. We find that, while strictly adhering to policy recommendations
increases efficiency, the nature of such recipes has a bigger effect. In other
words, while it is true that lack of discipline is detrimental to prescription
outcomes (a common defense of failed recommendations), it is more important
that such prescriptions consider the systemic and adaptive nature of the
policymaking process (something neglected by traditional technocratic advice)
- …