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Fuzzy OLAP association rules mining-based modular reinforcement learning approach for multiagent systems.

Multiagent systems and data mining have recently attracted considerable attention in the field of computing. Reinforcement learning is the most commonly used learning process for multiagent systems. However, it still has some drawbacks, including modeling other learning agents present in the domain as part of the state of the environment, and some states are experienced much less than others, or some state-action pairs are never visited during the learning phase. Further, before completing the learning process, an agent cannot exhibit a certain behavior in some states that may be experienced sufficiently. In this study, we propose a novel multiagent learning approach to handle these problems. Our approach is based on utilizing the mining process for modular cooperative learning systems. It incorporates fuzziness and online analytical processing (OLAP) based mining to effectively process the information reported by agents. First, we describe a fuzzy data cube OLAP architecture which facilitates effective storage and processing of the state information reported by agents. This way, the action of the other agent, not even in the visual environment. of the agent under consideration, can simply be predicted by extracting online association rules, a well-known data mining technique, from the constructed data cube. Second, we present a new action selection model, which is also based on association rules mining. Finally, we generalize not sufficiently experienced states, by mining multilevel association rules from the proposed fuzzy data cube. Experimental results obtained on two different versions of a well-known pursuit domain show the robustness and effectiveness of the proposed fuzzy OLAP mining based modular learning approach. Finally, we tested the scalability of the approach presented in this paper and compared it with our previous work on modular-fuzzy Q-learning and ordinary Q-learning.

Algorithms↗

Dynamical mechanisms of adaptation in multiagent systems.

We consider multiagent systems whose agents compete for resources using strategies with adaptable preferences. Diversity of initial preferences of strategies is introduced by randomly assigning virtual points to the strategies of each agent. When diversity increases, the successive appearance of scaling, kinetic sampling and waiting mechanisms shows that agent cooperation becomes increasingly important. Analyses yield excellent agreement with simulations over nine decades of data.

Journal Article↗

Anthropic agency: a multiagent system for physiological processes.

Multiagent systems are powerful and flexible tools for modelling and regulating complex phenomena. In fact, a way to manage the complexity of a phenomenon is to decompose it in such a way that each agent embeds the control model for a portion of the phenomenon. In this perspective, the cooperative interaction among the agents results in the controller for the whole phenomenon. Since the portions in which the phenomenon is decomposed may overlap, the actions the single agents undertake to regulate these portions may conflict; hence a balanced negotiation is required. A class of complex phenomena that present several difficulties in their satisfactory modelling and controlling is the class of physiological processes. The purpose of this paper is to introduce a general multiagent architecture, called anthropic agency, for the modelling and the regulation of complex physiological phenomena.

Animals↗

Modular fuzzy-reinforcement learning approach with internal model capabilities for multiagent systems.

To date, many researchers have proposed various methods to improve the learning ability in multiagent systems. However, most of these studies are not appropriate to more complex multiagent learning problems because the state space of each learning agent grows exponentially in terms of the number of partners present in the environment. Modeling other learning agents present in the domain as part of the state of the environment is not a realistic approach. In this paper, we combine advantages of the modular approach, fuzzy logic and the internal model in a single novel multiagent system architecture. The architecture is based on a fuzzy modular approach whose rule base is partitioned into several different modules. Each module deals with a particular agent in the environment and maps the input fuzzy sets to the action Q-values; these represent the state space of each learning module and the action space, respectively. Each module also uses an internal model table to estimate actions of the other agents. Finally, we investigate the integration of a parallel update method with the proposed architecture. Experimental results obtained on two different environments of a well-known pursuit domain show the effectiveness and robustness of the proposed multiagent architecture and learning approach.

Journal Article↗

Definitive surgery and multiagent systemic therapy for patients with localized Ewing sarcoma family of tumors: local outcome and prognostic factors.

BACKGROUND: The local management of Ewing sarcoma family of tumors (ESFT) often centers on the surgical resectability of the primary lesion and physician biases regarding differences in the morbidity between primary surgical and radiotherapeutic management. METHODS: The authors retrospectively reviewed the records of 33 patients with localized ESFT who underwent surgery and received systemic chemotherapy at St. Jude Children's Research Hospital (Memphis, TN). Two multiagent systemic chemotherapy regimens were used: 14 patients received vincristine, doxorubicin, cyclophosphamide, and actinomycin D (VACA), and 19 received VACA in combination with ifosphamide and etoposide. The primary tumor was surgically resected via a wide, local excision (n = 32) or a marginal excision (n = 1)performed either at diagnosis or after 3-5 months of systemic chemotherapy. Clinical outcome and prognostic factors for disease control were reported in the current study. RESULTS: The median follow-up for patients was 9.9 years. The 5-year and 10-year survival rates were 84.5% and 75.8%, respectively. At 5 years, the cumulative incidence of local disease recurrence was 12.5%, and the event-free survival (EFS) rate was 71.7%. The same values were found at 10 years. The site of tumor origin was a significant predictor of EFS. The survival rate of patients whose tumors arose in bone was 78.6%, and the survival rate of patients whose tumors originated in soft tissue was 25.0% (P = 0.028). No other factors investigated were predictive of outcome. CONCLUSIONS: Local disease control and overall outcome for patients with ESFT managed by multiagent systemic therapy and surgery was excellent. Local disease control rates remained near 90% at 10-year follow-up. Patients with extraosseous primary sites of disease may fare less well with this approach to therapy.

Adolescent↗

Coupled replicator equations for the dynamics of learning in multiagent systems.

Starting with a group of reinforcement-learning agents we derive coupled replicator equations that describe the dynamics of collective learning in multiagent systems. We show that, although agents model their environment in a self-interested way without sharing knowledge, a game dynamics emerges naturally through environment-mediated interactions. An application to rock-scissors-paper game interactions shows that the collective learning dynamics exhibits a diversity of competitive and cooperative behaviors. These include quasiperiodicity, stable limit cycles, intermittency, and deterministic chaos-behaviors that should be expected in heterogeneous multiagent systems described by the general replicator equations we derive.

Journal Article↗

Incorporating inertia into multiagent systems.

We consider a model that demonstrates the crucial role of inertia and stickiness in multiagent systems, based on the minority game. The inertia of an agent is introduced into the game model by allowing agents to apply hypothesis testing when choosing their best strategies, thereby reducing their reactivity toward changes in the environment. We find by extensive numerical simulations that our game shows a remarkable improvement of global cooperation throughout the whole phase space. In other words, the maladaptation behavior due to over-reaction of agents is removed. These agents are also shown to be advantageous over the standard ones, which are sometimes too sensitive to attain a fair success rate. We also calculate analytically the minimum amount of inertia needed to achieve the above improvement. Our calculation is consistent with the numerical simulation results. Finally, we review some related works in the field that show similar behaviors and compare them to our work.

Journal Article↗

A multiagent system enhancing home-care health services for chronic disease management.

In this paper, a multiagent system (MAS) is presented, aiming to enhance monitoring, surveillance, and educational services of a generic medical contact center (MCC) for chronic disease management. In such a home-care scenario, a persistent need arises for efficiently monitoring the patient contacts and the MCC's functionality, in order to effectively manage and interpret the large volume of medical data collected during the patient sessions with the system, and to assess the use of MCC resources. Software agents were adopted to provide the means to accomplish such real-time information-processing tasks, due to their autonomous, reactive and/or proactive nature, and their effectiveness in dynamic environments by incorporating coordination strategies. Specifically, the objective of the MAS is to monitor the MCC environment, detect important cases, and inform the healthcare and administrative personnel via alert messages, notifications, recommendations, and reports, prompting them for actions. The main aim of this paper is to present the overall design and implementation of a proposed MAS, emphasizing its functional model and architecture, as well as on the agent interactions and the knowledge-sharing mechanism incorporated, in the context of a generic MCC.

Artificial Intelligence↗

Quantitative measures of organization for multiagent systems.

A set of "information theoretic" measures has been developed to quantify the degree of constraint inherent in the organization of a multiagent system. Separate measures can be provided to quantify spatial organization, trophic organization and, more generally, the overall structure of interactions. The additive character of these quantities allows them to be distributed in various fashions among species and places in a way that allows one to assign an "Importance Index" to those taxa and places. In addition, a measure to gauge the degree of adaptation of a species to a particular environment is proffered. The proposed measures allow one to formulate the following hypotheses in quantitative fashion: (1). that any disturbance of an ecosystem at a location associated with a high spatial Importance Index will exert a greater impact on the population dynamics than will a similar disturbance aimed at a place where the values of these indexes are lower; (2). that any disturbance in an ecosystem affecting a particular species with high individual Importance Indexes will cause a greater impact on the overall population dynamics than will a disturbance aimed at a species with a lower values of these indexes; (3). that the ascendancy of evolving system has a propensity to increase. The precise quantitative formulation of these hypothesis would permit them to be tested via multiagent simulation. Estimating the probablities pertaining to these hypotheses presents a number of problems that merit discussion.

Information Systems↗

Strategy updating rules and strategy distributions in dynamical multiagent systems.

In the evolutionary version of the minority game, agents update their strategies (gene value p) in order to improve their performance. Motivated by the recent intriguing results obtained for prize-to-fine ratios, which are smaller than unity, we explore the system's dynamics with a strategy updating rule of the form p-->p+/-delta(p) (0<or=p<or=1). We find that the strategy distribution depends strongly on the values of the prize-to-fine ratio R, the length scale delta(p), and the type of boundary condition used. We show that these parameters determine the amplitude and the frequency of the temporal oscillations observed in the gene space. These regular oscillations are shown to be the main factors which determine the strategy distribution of the population. In addition, we find that the agents characterized by p=1/2 (a coin-tossing strategy) have the best chances of survival at asymptotically long times, regardless of the value of delta(p) and the boundary conditions used.

Journal Article↗

Effects of diversity on multiagent systems: minority games.

We consider a version of large population games whose agents compete for resources using strategies with adaptable preferences. The games can be used to model economic markets, ecosystems, or distributed control. Diversity of initial preferences of strategies is introduced by randomly assigning biases to the strategies of different agents. We find that diversity among the agents reduces their maladaptive behavior. We find interesting scaling relations with diversity for the variance and other parameters such as the convergence time, the fraction of fickle agents, and the variance of wealth, illustrating their dynamical origin. When diversity increases, the scaling dynamics is modified by kinetic sampling and waiting effects. Analyses yield excellent agreement with simulations.

Journal Article↗

[Multiagent system for individual artificial hip joint].

Based on the introduction of multi-agent and individual artificial hip joints, this paper reports a multi-agent design system for individual artificial hip joints. Three agents are defined, the first is to optimize the diameter of hip joint, the second for FEM, the third for simulation between the prosthesis and acetabulum cup. The paper lays emphasis on the second agent.

Acetabulum↗

A study of evolutionary multiagent models based on symbiosis.

Multiagent Systems with Symbiotic Learning and Evolution (Masbiole) has been proposed and studied, which is a new methodology of Multiagent Systems (MAS) based on symbiosis in the ecosystem. Masbiole employs a method of symbiotic learning and evolution where agents can learn or evolve according to their symbiotic relations toward others, i.e., considering the benefits/losses of both itself and an opponent. As a result, Masbiole can escape from Nash Equilibria and obtain better performances than conventional MAS where agents consider only their own benefits. This paper focuses on the evolutionary model of Masbiole, and its characteristics are examined especially with an emphasis on the behaviors of agents obtained by symbiotic evolution. In the simulations, two ideas suitable for the effective analysis of such behaviors are introduced; "Match Type Tile-world (MTT)" and "Genetic Network Programming (GNP)". MTT is a virtual model where tile-world is improved so that agents can behave considering their symbiotic relations. GNP is a newly developed evolutionary computation which has the directed graph type gene structure and enables to analyze the decision making mechanism of agents easily. Simulation results show that Masbiole can obtain various kinds of behaviors and better performances than conventional MAS in MTT by evolution.

Algorithms↗

Child fatality review: an international movement.

OBJECTIVE: This article discusses the multidisciplinary Child Fatality Review process in the US, Canada, and Australia, including common patterns, unique programs, changes over time, impact on multiagency systems, and future directions. METHOD: An open-ended survey was shared with teams listed in the directories of the Los Angeles County Inter-Agency Council on Child Abuse and Neglect National Center on Child Fatality Review (ICAN-NCFR). Responses were received from 58 state and local Child Fatality Review teams. RESULTS: Teams exist in all 50 states, Washington, DC, most Canadian provinces, and New South Wales, Australia. Team structure varies but generally includes a similar core membership, and most teams select cases from coroner/medical examiner or vital statistics records through established protocols. While most case review is conducted by local teams, state teams may review cases because of small size or sparse population or choose to review specific types of cases (e.g., Child Protective Services). State teams often support local review through training, resources, policy development, and political assistance. An increasing number of teams collect data and issue reports, often published on the internet, allowing teams to share resources. CONCLUSIONS: Teams have matured with time, often broadening their intake spectrum, membership and data collection, and developing and following through with case management or systems change recommendations. Teams continue to improve multiagency interaction and are committed to the prevention of child injury and death. The number of teams, as well as their scope and expertise, continues to increase, developing into a national/international system.

Australia↗

Ovarian tumors in relapsing acute lymphoblastic leukemia: a review of 23 cases.

Five cases of relapsing acute lymphocytic leukemia (ALL) presenting as an ovarian tumor have been treated at this institution, representing the largest reported series. In a review of the literature we identified 18 additional cases of ovarian leukemic relapse. Together, these 23 patients form the basis for this report. Abdominal pain is the most common presenting symptom of ovarian leukemia. An abdominal mass is usually palpable, and at least four patients had hydronephrosis. Nine patients had documented bilateral ovarian involvement; however, bilateral disease was not a poor prognostic sign. Most ovarian relapses occurred more than 36 months after the original diagnosis of ALL, with these "late'h relapsers responding more favorably to treatment than "early" relapsers. Definitive statements can not be made from a retrospective review of 23 case reports; however, salpingooophorectomy had no obvious advantage over simple biopsy, and there was no obvious advantage to the routine use of radiation therapy. Most failures in treating ovarian leukemia occurred within 2 years. Most failures were systemic rather than local, illustrating the need for aggressive multiagent systemic chemotherapy. Survival after ovarian leukemic relapse is possible, with eight of the 23 patients alive and in complete continuous remission following the ovarian relapse (median follow-up since relapse, 42 months; range, 2 to 135+ months). With the use of more intensive chemotherapy in recent protocols, the frequency of ovarian leukemic relapses appears to be decreasing. At this institution, no child with ALL diagnosed in the 1980s has subsequently developed an ovarian relapse.

Adolescent↗

A multiagent genetic algorithm for global numerical optimization.

In this paper, multiagent systems and genetic algorithms are integrated to form a new algorithm, multiagent genetic algorithm (MAGA), for solving the global numerical optimization problem. An agent in MAGA represents a candidate solution to the optimization problem in hand. All agents live in a latticelike environment, with each agent fixed on a lattice-point. In order to increase energies, they compete or cooperate with their neighbors, and they can also use knowledge. Making use of these agent-agent interactions, MAGA realizes the purpose of minimizing the objective function value. Theoretical analyzes show that MAGA converges to the global optimum. In the first part of the experiments, ten benchmark functions are used to test the performance of MAGA, and the scalability of MAGA along the problem dimension is studied with great care. The results show that MAGA achieves a good performance when the dimensions are increased from 20-10,000. Moreover, even when the dimensions are increased to as high as 10,000, MAGA still can find high quality solutions at a low computational cost. Therefore, MAGA has good scalability and is a competent algorithm for solving high dimensional optimization problems. To the best of our knowledge, no researchers have ever optimized the functions with 10,000 dimensions by means of evolution. In the second part of the experiments, MAGA is applied to a practical case, the approximation of linear systems, with a satisfactory result.

Journal Article↗

Ewing's sarcoma of the mobile spine.

STUDY DESIGN: A retrospective analysis was performed. OBJECTIVES: To determine the oncological outcome of patients with nonmetastatic Ewing's sarcoma of the mobile spine treated with systemic multiagent chemotherapy combined with radiation therapy for definitive local control. SUMMARY OF BACKGROUND DATA: To our knowledge, there are no studies that evaluate the oncological outcome of patients with nonmetastatic Ewing's sarcoma of the mobile spine treated with systemic chemotherapy and radiation therapy for definitive local control. METHODS: Thirteen patients with nonmetastatic Ewing's sarcoma of the mobile spine were treated with high-dose multiagent chemotherapy combined with radiation therapy for definitive local control from 1971 to 2000 at a single institution. Patients were observed for a minimum of 2 years or until death. Neurological function, local recurrence, distant relapse, and treatment-related complications were evaluated. RESULTS: There were 8 females and 5 males with a mean age of 19 years (ranging from 7-26 years). The mean follow-up time was 65 months (median 28 months; ranging from 2 to 218 months). All patients presented with pain. Motor deficits were present in 6 patients. Ten patients had a decompressive laminectomy. Improved pain control, as determined by narcotic use, was noted in 12 (92%) patients. Ten patients maintained or improved motor function by at least 1 Frankel grade, while 3 had deterioration of motor function. The disease-free survival rate was 49% and 36% at 5 and 10 years. Five (38%) patients were free of disease at last follow-up. Seven patients developed metastatic disease. Three (23%) patients developed a local recurrence. One of these patients had paraplegia associated with the local recurrence. Five patients developed 8 treatment-related complications. Four of the 10 (40%) patients that had a laminectomy developed progressive kyphosis. Two of these patients also developed late-onset cauda equina syndrome along with the deformity. One of these patients also developed cardiomyopathy associated with adriamycin cardiotoxicity. One patient developed a nonhealing pressure ulcerover a prominent spinous process. CONCLUSIONS: The current study provides historical data on a relatively homogeneous group of patients withEwing's sarcoma of the mobile spine treated with multiagent chemotherapy combined with radiation therapy for definitive local control. Systemic chemotherapy combined with current spinal resection and reconstruction techniques may lead to improved oncological and clinical outcomes.

Adolescent↗