Bio-inspired computation: where we stand and what's next

In recent years, the research community has witnessed an explosion of literature dealing with the adaptation of behavioral patterns and social phenomena observed in nature towards efficiently solving complex computational tasks. This trend has been especially dramatic in what relates to optimization problems, mainly due to the unprecedented complexity of problem instances, arising from a diverse spectrum of domains such as transportation, logistics, energy, climate, social networks, health and industry 4.0, among many others. Notwithstanding this upsurge of activity, research in this vibrant topic should be steered towards certain areas that, despite their eventual value and impact on the field of bio-inspired computation, still remain insufficiently explored to date. The main purpose of this paper is to outline the state of the art and to identify open challenges concerning the most relevant areas within bio-inspired optimization. An analysis and discussion are also carried out over the general trajectory followed in recent years by the community working in this field, thereby highlighting the need for reaching a consensus and joining forces towards achieving valuable insights into the understanding of this family of optimization techniques

Bio-inspired computation: where we stand and what's next

In recent years, the research community has witnessed an explosion of literature dealing with the adaptation of behavioral patterns and social phenomena observed in nature towards efficiently solving complex computational tasks. This trend has been especially dramatic in what relates to optimization problems, mainly due to the unprecedented complexity of problem instances, arising from a diverse spectrum of domains such as transportation, logistics, energy, climate, social networks, health and industry 4.0, among many others. Notwithstanding this upsurge of activity, research in this vibrant topic should be steered towards certain areas that, despite their eventual value and impact on the field of bio-inspired computation, still remain insufficiently explored to date. The main purpose of this paper is to outline the state of the art and to identify open challenges concerning the most relevant areas within bio-inspired optimization. An analysis and discussion are also carried out over the general trajectory followed in recent years by the community working in this field, thereby highlighting the need for reaching a consensus and joining forces towards achieving valuable insights into the understanding of this family of optimization techniques

Automated Design of Metaheuristic Algorithms: A Survey

Metaheuristics have gained great success in academia and practice because their search logic can be applied to any problem with available solution representation, solution quality evaluation, and certain notions of locality. Manually designing metaheuristic algorithms for solving a target problem is criticized for being laborious, error-prone, and requiring intensive specialized knowledge. This gives rise to increasing interest in automated design of metaheuristic algorithms. With computing power to fully explore potential design choices, the automated design could reach and even surpass human-level design and could make high-performance algorithms accessible to a much wider range of researchers and practitioners. This paper presents a broad picture of automated design of metaheuristic algorithms, by conducting a survey on the common grounds and representative techniques in terms of design space, design strategies, performance evaluation strategies, and target problems in this field

Π18.4 – Έκθεση 4ου Επιστημονικού Workshop

Το συγκεκριμένο παραδοτέο αφορά το 4ο Επιστημονικό Workshop του έργου που πραγματοποιήθηκε στον Πειραιά, το χρονικό διάστημα 2-3 Απριλίου 201

Machine learning for improving heuristic optimisation

Heuristics, metaheuristics and hyper-heuristics are search methodologies which have been preferred by many researchers and practitioners for solving computationally hard combinatorial optimisation problems, whenever the exact methods fail to produce high quality solutions in a reasonable amount of time. In this thesis, we introduce an advanced machine learning technique, namely, tensor analysis, into the field of heuristic optimisation. We show how the relevant data should be collected in tensorial form, analysed and used during the search process. Four case studies are presented to illustrate the capability of single and multi-episode tensor analysis processing data with high and low abstraction levels for improving heuristic optimisation. A single episode tensor analysis using data at a high abstraction level is employed to improve an iterated multi-stage hyper-heuristic for cross-domain heuristic search. The empirical results across six different problem domains from a hyper-heuristic benchmark show that significant overall performance improvement is possible. A similar approach embedding a multi-episode tensor analysis is applied to the nurse rostering problem and evaluated on a benchmark of a diverse collection of instances, obtained from different hospitals across the world. The empirical results indicate the success of the tensor-based hyper-heuristic, improving upon the best-known solutions for four particular instances. Genetic algorithm is a nature inspired metaheuristic which uses a population of multiple interacting solutions during the search. Mutation is the key variation operator in a genetic algorithm and adjusts the diversity in a population throughout the evolutionary process. Often, a fixed mutation probability is used to perturb the value at each locus, representing a unique component of a given solution. A single episode tensor analysis using data with a low abstraction level is applied to an online bin packing problem, generating locus dependent mutation probabilities. The tensor approach improves the performance of a standard genetic algorithm on almost all instances, significantly. A multi-episode tensor analysis using data with a low abstraction level is embedded into multi-agent cooperative search approach. The empirical results once again show the success of the proposed approach on a benchmark of flow shop problem instances as compared to the approach which does not make use of tensor analysis. The tensor analysis can handle the data with different levels of abstraction leading to a learning approach which can be used within different types of heuristic optimisation methods based on different underlying design philosophies, indeed improving their overall performance

Machine learning for improving heuristic optimisation

Heuristics, metaheuristics and hyper-heuristics are search methodologies which have been preferred by many researchers and practitioners for solving computationally hard combinatorial optimisation problems, whenever the exact methods fail to produce high quality solutions in a reasonable amount of time. In this thesis, we introduce an advanced machine learning technique, namely, tensor analysis, into the field of heuristic optimisation. We show how the relevant data should be collected in tensorial form, analysed and used during the search process. Four case studies are presented to illustrate the capability of single and multi-episode tensor analysis processing data with high and low abstraction levels for improving heuristic optimisation. A single episode tensor analysis using data at a high abstraction level is employed to improve an iterated multi-stage hyper-heuristic for cross-domain heuristic search. The empirical results across six different problem domains from a hyper-heuristic benchmark show that significant overall performance improvement is possible. A similar approach embedding a multi-episode tensor analysis is applied to the nurse rostering problem and evaluated on a benchmark of a diverse collection of instances, obtained from different hospitals across the world. The empirical results indicate the success of the tensor-based hyper-heuristic, improving upon the best-known solutions for four particular instances. Genetic algorithm is a nature inspired metaheuristic which uses a population of multiple interacting solutions during the search. Mutation is the key variation operator in a genetic algorithm and adjusts the diversity in a population throughout the evolutionary process. Often, a fixed mutation probability is used to perturb the value at each locus, representing a unique component of a given solution. A single episode tensor analysis using data with a low abstraction level is applied to an online bin packing problem, generating locus dependent mutation probabilities. The tensor approach improves the performance of a standard genetic algorithm on almost all instances, significantly. A multi-episode tensor analysis using data with a low abstraction level is embedded into multi-agent cooperative search approach. The empirical results once again show the success of the proposed approach on a benchmark of flow shop problem instances as compared to the approach which does not make use of tensor analysis. The tensor analysis can handle the data with different levels of abstraction leading to a learning approach which can be used within different types of heuristic optimisation methods based on different underlying design philosophies, indeed improving their overall performance

Heuristinen yhteistyöhaku ohjelmistoagenttien avulla

Parallel algorithms extend the notion of sequential algorithms by permitting the simultaneous execution of independent computational steps. When the independence constraint is lifted and executions can freely interact and intertwine, parallel algorithms become concurrent and may behave in a nondeterministic way. Parallelism has over the years slowly risen to be a standard feature of high-performance computing, but concurrency, being even harder to reason about, is still considered somewhat notorious and undesirable. As such, the implicit randomness available in concurrency is rarely made use of in algorithms. This thesis explores concurrency as a means to facilitate algorithmic cooperation in a heuristic search setting. We use agents, cooperating software entities, to build a single-source shortest path (SSSP) search algorithm based on parallelized A∗, dubbed A!. We show how asynchronous information sharing gives rise to implicit randomness, which cooperating agents use in A! to maintain a collective secondary ranking heuristic and focus search space exploration. We experimentally show that A! consistently outperforms both vanilla A∗ and a noncooperative, explicitly randomized A∗ variant in the standard n-puzzle sliding tile problem context. The results indicate that A! performance increases with the addition of more agents, but that the returns are diminishing. A! is observed to be sensitive to heuristic improvement, but also constrained by search overhead from limited path diversity. A hybrid approach combining both implicit and explicit randomness is also evaluated and found to not be an improvement over A! alone. The studied A! implementation based on vanilla A∗ is not as such competitive against state-of-the-art parallel A∗ algorithms, but rather a first step in applying concurrency to speed up heuristic SSSP search. The empirical results imply that concurrency and nondeterministic cooperation can successfully be harnessed in algorithm design, inviting further inquiry into algorithms of this kind.Rinnakkaisalgoritmit sallivat useiden riippumattomien ohjelmakäskyjen suorittamisen samanaikaisesti. Kun riippumattomuusrajoite poistetaan ja käskyjen suorittamisen järjestystä ei hallita, rinnakkaisalgoritmit voivat käskysuoritusten samanaikaisuuden vuoksi käyttäytyä epädeterministisellä tavalla. Rinnakkaisuus on vuosien saatossa noussut tärkeään rooliin tietotekniikassa ja samalla hallitsematonta samanaikaisuutta on yleisesti alettu pitää ongelmallisena ja ei-toivottuna. Samanaikaisuudesta kumpuavaa epäsuoraa satunnaisuutta hyödynnetään harvoin algoritmeissa. Tämä työ käsittelee käskysuoritusten samanaikaisuuden hyödyntämistä osana heuristista yhteistyöhakua. Työssä toteutetaan agenttien, yhteistyökykyisten ohjelmistokomponenttien, avulla uudenlainen A!-hakualgoritmi. A! perustuu rinnakkaiseen A∗ -algoritmiin, joka ratkaisee yhden lähteen lyhimmän polun hakuongelman. Työssä näytetään, miten ajastamaton viestintä agenttien välillä johtaa epäsuoraan satunnaisuuteen, jota A!-agentit kollektiivisesti hyödyntävät toissijaisen järjestämisheuristiikan ylläpitämisessä ja edelleen haun kohdentamisessa. Työssä näytetään kokeellisesti, kuinka A! suoriutuu niin tavanomaista kuin satunnaistettuakin A∗ -algoritmia paremmin n-puzzle pulmapelin ratkaisemisessa. Tulokset osoittavat, että A!-algoritmin suorituskyky kasvaa lisäagenttien myötä, mutta myös sen, että hyöty on joka lisäyksen jälkeen suhteellisesti pienempi. A! osoittautuu heuristiikan hyödyntämisen osalta verrokkeja herkemmäksi, mutta myös etsintäpolkujen monimuotoisuuden kannalta vaatimattomaksi. Yksinkertaisen suoraa ja epäsuoraa satunnaisuutta yhdistävän hybridialgoritmin ei todeta tuovan lisäsuorituskykyä A!-algoritmiin verrattuna. Empiiriset kokeet osoittavat, että hallitsematonta samanaikaisuutta ja epädeterminististä yhteistyötä voi onnistuneesti hyödyntää algoritmisuunnittelussa, mikä kannustaa lisätutkimuksiin näitä soveltavan algoritmiikan parissa