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Erschienen in: Acta Mechanica 8/2019

01.06.2019 | Original Paper

Quantum evolutionary algorithm with rotational gate and \(H_\epsilon \)-gate updating in real and integer domains for optimization

verfasst von: M. Kamalinejad, H. Arzani, A. Kaveh

Erschienen in: Acta Mechanica | Ausgabe 8/2019

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Abstract

Attempts to find new advanced methods for optimization and decision-making problems in controlling real tasks have become today’s trend in mathematics, mechanics, and computer science and many other disciplines. Meta-heuristics approaches provide powerful means to find an algorithm based on nature or physical laws and phenomena such as Newtonian laws in collision (CBO), and space laws and parallel verses (MVO) and many other laws. The recently developed approach by Han and Kim (IEEE Trans. Evolut. Comput. 6(6):580–593, 2002) is based on quantum mechanics laws. A quantum evolutionary algorithm (QEA) uses Q-bit individuals in binary code analogous to genes in the conventional genetic algorithm. In different stages of iterations, the Q-bit solutions are updated using the prominent quantum gate rotational gate and \(H_\epsilon \)-gate. This paper is devoted to the assessment of the QEA using some well-known optimization problems. QEA has excellent features such as practical exploration and exploitation of domain space due to utilizing a binary approach for generation of the solutions and rotational gate updating based on the probability of 0 or 1. Here, \(H_\epsilon \)-gate and parallel phase are used to change the path of finding the optimal solution for escaping from local optima.
Literatur
1.
Zurück zum Zitat Han, K.-H., Kim, J.-H.: Quantum-inspired evolutionary algorithm for a class of combinatorial optimization. IEEE Trans. Evolut. Comput. 6(6), 580–593 (2002)MathSciNetCrossRef Han, K.-H., Kim, J.-H.: Quantum-inspired evolutionary algorithm for a class of combinatorial optimization. IEEE Trans. Evolut. Comput. 6(6), 580–593 (2002)MathSciNetCrossRef
3.
Zurück zum Zitat Lloyd, S.: Quantum-mechanical computers. Sc. Am. 273(4), 140–145 (1995)CrossRef Lloyd, S.: Quantum-mechanical computers. Sc. Am. 273(4), 140–145 (1995)CrossRef
5.
Zurück zum Zitat Church, A., Turing, A.M.: On computable numbers, with an application to the Entscheidungsproblem. Proc. Lond. Math. Soc. 42(2s), 230–265 (1937)MathSciNetMATH Church, A., Turing, A.M.: On computable numbers, with an application to the Entscheidungsproblem. Proc. Lond. Math. Soc. 42(2s), 230–265 (1937)MathSciNetMATH
6.
Zurück zum Zitat Deutsch, D.: Quantum theory, the Church–Turing principle and the universal quantum computer. Proc. Lond. R. Soc. A400(1818), 97–117 (1985)MathSciNetMATHCrossRef Deutsch, D.: Quantum theory, the Church–Turing principle and the universal quantum computer. Proc. Lond. R. Soc. A400(1818), 97–117 (1985)MathSciNetMATHCrossRef
8.
Zurück zum Zitat Shor, P. W.: Algorithms for quantum computation: discrete logarithms and factoring. In: Proceedings of the 35th Annual Symposium on Foundations of Computer Science (1994) Shor, P. W.: Algorithms for quantum computation: discrete logarithms and factoring. In: Proceedings of the 35th Annual Symposium on Foundations of Computer Science (1994)
9.
Zurück zum Zitat Narayanan, A., Moore, M.: Quantum-inspired genetic algorithms. In: Paper presented at the Evolutionary Computation, 1996. Proceedings of IEEE International Conference on Evolutionary Computation (1996) Narayanan, A., Moore, M.: Quantum-inspired genetic algorithms. In: Paper presented at the Evolutionary Computation, 1996. Proceedings of IEEE International Conference on Evolutionary Computation (1996)
10.
Zurück zum Zitat Shor, P.W.: Polynomial-time algorithms for prime factorization and discrete logarithms on a quantum computer. SIAM J. Comput. 26(5), 1484 (1997)MathSciNetMATHCrossRef Shor, P.W.: Polynomial-time algorithms for prime factorization and discrete logarithms on a quantum computer. SIAM J. Comput. 26(5), 1484 (1997)MathSciNetMATHCrossRef
11.
Zurück zum Zitat Rivest, R.L., Shamir, A., Adleman, L.: A method for obtaining digital signatures and public-key cryptosystems. Commun. ACM 21(2), 120–126 (1978)MathSciNetMATHCrossRef Rivest, R.L., Shamir, A., Adleman, L.: A method for obtaining digital signatures and public-key cryptosystems. Commun. ACM 21(2), 120–126 (1978)MathSciNetMATHCrossRef
12.
Zurück zum Zitat Grover, L.K.: Quantum mechanics helps in searching for a needle in a haystack. Phys. Rev. Lett. 79(2), 325 (1997)CrossRef Grover, L.K.: Quantum mechanics helps in searching for a needle in a haystack. Phys. Rev. Lett. 79(2), 325 (1997)CrossRef
14.
Zurück zum Zitat Koiran, P., Nesme, V., Portier, N.: A quantum lower bound for the query complexity of Simon’s problem. In: Paper presented at the International Colloquium on Automata, Languages, and Programming (2005) Koiran, P., Nesme, V., Portier, N.: A quantum lower bound for the query complexity of Simon’s problem. In: Paper presented at the International Colloquium on Automata, Languages, and Programming (2005)
15.
Zurück zum Zitat Griffiths, D.: Introduction to Quantum Mechanics. Prentice Hall, Upper Saddle River (1994) Griffiths, D.: Introduction to Quantum Mechanics. Prentice Hall, Upper Saddle River (1994)
16.
Zurück zum Zitat Alpaydin, E.: Introduction to Machine Learning. MIT Press, Boca Raton (2014)MATH Alpaydin, E.: Introduction to Machine Learning. MIT Press, Boca Raton (2014)MATH
17.
Zurück zum Zitat Fogel, D.: Evolutionary Computation: Toward a New Philosophy of Machine Intelligence. IEEE Press, Piscataway, NJ (1995)MATH Fogel, D.: Evolutionary Computation: Toward a New Philosophy of Machine Intelligence. IEEE Press, Piscataway, NJ (1995)MATH
18.
Zurück zum Zitat Back, T.: Evolutionary Algorithms in Theory and Practice: Evolution Strategies, Evolutionary Programming, Genetic Algorithms. Oxford University Press, Oxford (1996)MATH Back, T.: Evolutionary Algorithms in Theory and Practice: Evolution Strategies, Evolutionary Programming, Genetic Algorithms. Oxford University Press, Oxford (1996)MATH
19.
Zurück zum Zitat Haftka, R., Gurdal, Z.: Element of Structural Optimization, 3rd edn. Kluwer Academic Publisher, Dordrecht (1992)MATHCrossRef Haftka, R., Gurdal, Z.: Element of Structural Optimization, 3rd edn. Kluwer Academic Publisher, Dordrecht (1992)MATHCrossRef
20.
Zurück zum Zitat Elishakoff, I., Haftka, R., Fang, J.: Structural design under bounded uncertainty—optimization with anti-optimization. Comput. Struct. 53(6), 1401–1405 (1994)MATHCrossRef Elishakoff, I., Haftka, R., Fang, J.: Structural design under bounded uncertainty—optimization with anti-optimization. Comput. Struct. 53(6), 1401–1405 (1994)MATHCrossRef
21.
Zurück zum Zitat Rozvany, G., Zhou, M.: The COC algorithm, part I: cross-section optimization or sizing. Comput. Methods Appl. Mech. Eng. 89(1–3), 281–308 (1991)CrossRef Rozvany, G., Zhou, M.: The COC algorithm, part I: cross-section optimization or sizing. Comput. Methods Appl. Mech. Eng. 89(1–3), 281–308 (1991)CrossRef
22.
Zurück zum Zitat Sofge, D. A.: Prospective algorithms for quantum evolutionary computation. In: Paper Presented at the Proceedings of the 2nd Quantum International Symposium (2008) Sofge, D. A.: Prospective algorithms for quantum evolutionary computation. In: Paper Presented at the Proceedings of the 2nd Quantum International Symposium (2008)
23.
Zurück zum Zitat Nielsen, M.A., Chuang, I.L.: Quantum Computation and Quantum Information. Cambridge University Press, Cambridge (2000)MATH Nielsen, M.A., Chuang, I.L.: Quantum Computation and Quantum Information. Cambridge University Press, Cambridge (2000)MATH
24.
Zurück zum Zitat Han, K.H., Kim, J.H.: On the analysis of the quantum-inspired evolutionary algorithm with a single individual. In: 2006 IEEE International Conference on Evolutionary Computation. IEEE, pp. 2622–2629 (2006) Han, K.H., Kim, J.H.: On the analysis of the quantum-inspired evolutionary algorithm with a single individual. In: 2006 IEEE International Conference on Evolutionary Computation. IEEE, pp. 2622–2629 (2006)
25.
Zurück zum Zitat Han, K.-H., Kim, J.-H.: Quantum-inspired evolutionary algorithms with a new termination criterion, h-epsilon gate, and two-phase scheme. IEEE Trans. Evolut. Comput. 8, 156–169 (2004)CrossRef Han, K.-H., Kim, J.-H.: Quantum-inspired evolutionary algorithms with a new termination criterion, h-epsilon gate, and two-phase scheme. IEEE Trans. Evolut. Comput. 8, 156–169 (2004)CrossRef
26.
Zurück zum Zitat Ragsdell, K., Phillips, D.: Optimal design of a class of welded structures using geometric programming. J. Eng. Ind. 98(3), 1021–1025 (1976)CrossRef Ragsdell, K., Phillips, D.: Optimal design of a class of welded structures using geometric programming. J. Eng. Ind. 98(3), 1021–1025 (1976)CrossRef
27.
Zurück zum Zitat Deb, K.: Optimal design of a welded beam via genetic algorithms. AIAA J. 29(11), 2013–2015 (1991)CrossRef Deb, K.: Optimal design of a welded beam via genetic algorithms. AIAA J. 29(11), 2013–2015 (1991)CrossRef
28.
Zurück zum Zitat Coello, C.A.C.: Use of a self-adaptive penalty approach for engineering optimization problems. Comput. Ind. 41(2), 113–127 (2000)CrossRef Coello, C.A.C.: Use of a self-adaptive penalty approach for engineering optimization problems. Comput. Ind. 41(2), 113–127 (2000)CrossRef
29.
Zurück zum Zitat Coello, C.A.C., Montes, E.M.: Constraint-handling in genetic algorithms through the use of dominance-based tournament selection. Adv. Eng. Inform. 16(3), 193–203 (2002)CrossRef Coello, C.A.C., Montes, E.M.: Constraint-handling in genetic algorithms through the use of dominance-based tournament selection. Adv. Eng. Inform. 16(3), 193–203 (2002)CrossRef
30.
Zurück zum Zitat He, Q., Wang, L.: An effective co-evolutionary particle swarm optimization for constrained engineering design problems. Eng. Appl. Artif. Intell. 20(1), 89–99 (2007)CrossRef He, Q., Wang, L.: An effective co-evolutionary particle swarm optimization for constrained engineering design problems. Eng. Appl. Artif. Intell. 20(1), 89–99 (2007)CrossRef
31.
Zurück zum Zitat Mezura-Montes, E., Coello, C.A.C.: An empirical study about the usefulness of evolution strategies to solve constrained optimization problems. Int. J. Gen. Syst. 37(4), 443–473 (2008)MathSciNetMATHCrossRef Mezura-Montes, E., Coello, C.A.C.: An empirical study about the usefulness of evolution strategies to solve constrained optimization problems. Int. J. Gen. Syst. 37(4), 443–473 (2008)MathSciNetMATHCrossRef
32.
Zurück zum Zitat Kaveh, A., Talatahari, S.: A novel heuristic optimization method: charged system search. Acta Mech. 213(3–4), 267–289 (2010)MATHCrossRef Kaveh, A., Talatahari, S.: A novel heuristic optimization method: charged system search. Acta Mech. 213(3–4), 267–289 (2010)MATHCrossRef
33.
Zurück zum Zitat Kaveh, A., Mahdavi, V.R.: Colliding Bodies Optimization: Extensions and Applications. Springer, Berlin (2015)MATHCrossRef Kaveh, A., Mahdavi, V.R.: Colliding Bodies Optimization: Extensions and Applications. Springer, Berlin (2015)MATHCrossRef
34.
Zurück zum Zitat Kaveh, A.: Advances in Metaheuristic Algorithm for Optimal Design of Structures, 2nd edn. Springer International Publishing, Basel (2017)MATHCrossRef Kaveh, A.: Advances in Metaheuristic Algorithm for Optimal Design of Structures, 2nd edn. Springer International Publishing, Basel (2017)MATHCrossRef
35.
Zurück zum Zitat Sandgren, E.: Nonlinear integer and discrete programming in mechanical design. In: Paper Presented at the Proceeding of the ASME Design Technology Conference (1988) Sandgren, E.: Nonlinear integer and discrete programming in mechanical design. In: Paper Presented at the Proceeding of the ASME Design Technology Conference (1988)
36.
Zurück zum Zitat Kannan, B., Kramer, S.N.: An augmented Lagrange multiplier based method for mixed integer discrete continuous optimization and its applications to mechanical design. J. Mech. Des. 116(2), 405–411 (1994)CrossRef Kannan, B., Kramer, S.N.: An augmented Lagrange multiplier based method for mixed integer discrete continuous optimization and its applications to mechanical design. J. Mech. Des. 116(2), 405–411 (1994)CrossRef
37.
Zurück zum Zitat Deb, K., Gene, A.: A robust optimal design technique for mechanical component design. In: Dasgupta, D., Michalewicz, Z. (eds.) Evolutionary Algorithms in Engineering Applications, pp. 497–514. Springer, Berlin (1997)CrossRef Deb, K., Gene, A.: A robust optimal design technique for mechanical component design. In: Dasgupta, D., Michalewicz, Z. (eds.) Evolutionary Algorithms in Engineering Applications, pp. 497–514. Springer, Berlin (1997)CrossRef
38.
Zurück zum Zitat Kaveh, A., Talatahari, S.: An improved ant colony optimization for constrained engineering design problems. Eng. Comput. 27(1), 155–182 (2010)MATHCrossRef Kaveh, A., Talatahari, S.: An improved ant colony optimization for constrained engineering design problems. Eng. Comput. 27(1), 155–182 (2010)MATHCrossRef
39.
Zurück zum Zitat Kaveh, A., Mahdavi, V.R.: Two-dimensional colliding bodies algorithm for optimal design of truss structures. Adv. Eng. Softw. 83, 70–79 (2015)CrossRef Kaveh, A., Mahdavi, V.R.: Two-dimensional colliding bodies algorithm for optimal design of truss structures. Adv. Eng. Softw. 83, 70–79 (2015)CrossRef
40.
Zurück zum Zitat Gandomi, A.: Interior search algorithm (ISA): a novel approach for global optimization. ISA Trans. 53(54), 1168–1183 (2014)CrossRef Gandomi, A.: Interior search algorithm (ISA): a novel approach for global optimization. ISA Trans. 53(54), 1168–1183 (2014)CrossRef
41.
Zurück zum Zitat Mirjalili, S., Mirjalili, S., Hatamlou, A.: Multi-verse optimizer: a nature-inspired algorithm for global optimization. Neural Comput. Appl. 27(2), 495–513 (2015)CrossRef Mirjalili, S., Mirjalili, S., Hatamlou, A.: Multi-verse optimizer: a nature-inspired algorithm for global optimization. Neural Comput. Appl. 27(2), 495–513 (2015)CrossRef
42.
Zurück zum Zitat Sadollah, A., Bahreininejad, A., Eskandar, H., Hamdi, M.: Mine blast algorithm: a new population based algorithm for solving constrained engineering optimization problems. Appl. Soft Comput. 13(5), 2592–2612 (2013)CrossRef Sadollah, A., Bahreininejad, A., Eskandar, H., Hamdi, M.: Mine blast algorithm: a new population based algorithm for solving constrained engineering optimization problems. Appl. Soft Comput. 13(5), 2592–2612 (2013)CrossRef
43.
Zurück zum Zitat Deb, K., Goyal, M.: A combined genetic adaptive search (GeneAS) for engineering design. Comput. Sci. Inform. 26, 30–45 (1996) Deb, K., Goyal, M.: A combined genetic adaptive search (GeneAS) for engineering design. Comput. Sci. Inform. 26, 30–45 (1996)
44.
Zurück zum Zitat Gandomi, A., Yang, X.-S., Alavi, A.: Cuckoo search algorithm: a metaheuristic approach to solve structural optimization problems. Eng. Comput. 29(1), 17–35 (2013)CrossRef Gandomi, A., Yang, X.-S., Alavi, A.: Cuckoo search algorithm: a metaheuristic approach to solve structural optimization problems. Eng. Comput. 29(1), 17–35 (2013)CrossRef
45.
Zurück zum Zitat Kazemzadeh Azad, S.: Enhanced hybrid metaheuristic algorithms for optimal sizing of steel truss structures with numerous discrete variables. Struct. Multidiscip. Optim. 55, 2159–2180 (2017)CrossRef Kazemzadeh Azad, S.: Enhanced hybrid metaheuristic algorithms for optimal sizing of steel truss structures with numerous discrete variables. Struct. Multidiscip. Optim. 55, 2159–2180 (2017)CrossRef
46.
Zurück zum Zitat Kazemzadeh Azad, S., Hasançebi, O., Kazemzadeh, Azad S.: Upper bound strategy for metaheuristic based design optimization of steel frames. Adv. Eng. Softw. 57, 19–32 (2013)CrossRef Kazemzadeh Azad, S., Hasançebi, O., Kazemzadeh, Azad S.: Upper bound strategy for metaheuristic based design optimization of steel frames. Adv. Eng. Softw. 57, 19–32 (2013)CrossRef
47.
Zurück zum Zitat Kaveh, A., Ilchi Ghazaan, M.: Meta-heuristic Algorithms for Optimal Design of Real-Size Structures. Springer, Basel (2018)MATHCrossRef Kaveh, A., Ilchi Ghazaan, M.: Meta-heuristic Algorithms for Optimal Design of Real-Size Structures. Springer, Basel (2018)MATHCrossRef
48.
Zurück zum Zitat Kazemzadeh Azad, S., Hasançebi, O.: Discrete sizing optimization of steel trusses under multiple displacement constraints and load cases using guided stochastic search technique. Struct. Multidiscip. Optim. 52, 383–404 (2015)CrossRef Kazemzadeh Azad, S., Hasançebi, O.: Discrete sizing optimization of steel trusses under multiple displacement constraints and load cases using guided stochastic search technique. Struct. Multidiscip. Optim. 52, 383–404 (2015)CrossRef
49.
Zurück zum Zitat Kazemzadeh Azad, S.: Seeding the initial population with feasible solutions in metaheuristic optimization of steel trusses. Eng. Optim. 50, 89–105 (2018)MathSciNetCrossRef Kazemzadeh Azad, S.: Seeding the initial population with feasible solutions in metaheuristic optimization of steel trusses. Eng. Optim. 50, 89–105 (2018)MathSciNetCrossRef
50.
Zurück zum Zitat Zhang, M., Luo, W., Wang, X.: Differential evolution with dynamic stochastic selection for constrained optimization. Inf. Sci. 178(15), 3043–3074 (2008)CrossRef Zhang, M., Luo, W., Wang, X.: Differential evolution with dynamic stochastic selection for constrained optimization. Inf. Sci. 178(15), 3043–3074 (2008)CrossRef
51.
Zurück zum Zitat Liu, H., Cai, Z., Wang, Y.: Hybridizing particle swarm optimization with differential evolution for constrained numerical and engineering optimization. Appl. Soft Comput. 10(2), 629–640 (2010)CrossRef Liu, H., Cai, Z., Wang, Y.: Hybridizing particle swarm optimization with differential evolution for constrained numerical and engineering optimization. Appl. Soft Comput. 10(2), 629–640 (2010)CrossRef
52.
Zurück zum Zitat Ray, T., Saini, P.: Engineering design optimization using a swarm with an intelligent information sharing among individuals. Eng. Optim. 33(6), 735–748 (2001)CrossRef Ray, T., Saini, P.: Engineering design optimization using a swarm with an intelligent information sharing among individuals. Eng. Optim. 33(6), 735–748 (2001)CrossRef
53.
Zurück zum Zitat Tsai, J.-F.: Global optimization of nonlinear fractional programming problems in engineering design. Eng. Optim. 37(4), 399–409 (2005)MathSciNetCrossRef Tsai, J.-F.: Global optimization of nonlinear fractional programming problems in engineering design. Eng. Optim. 37(4), 399–409 (2005)MathSciNetCrossRef
54.
Zurück zum Zitat Chickermane, H., Gea, H.: Structural optimization using a new local approximation method. Int. J. Numer. Methods Eng. 39(5), 829–846 (1996)MathSciNetMATHCrossRef Chickermane, H., Gea, H.: Structural optimization using a new local approximation method. Int. J. Numer. Methods Eng. 39(5), 829–846 (1996)MathSciNetMATHCrossRef
55.
Zurück zum Zitat Cheng, M.-Y., Prayogo, D.: Symbiotic organisms search: a new metaheuristic optimization algorithm. Comput. Struct. 139, 98–112 (2014)CrossRef Cheng, M.-Y., Prayogo, D.: Symbiotic organisms search: a new metaheuristic optimization algorithm. Comput. Struct. 139, 98–112 (2014)CrossRef
57.
Zurück zum Zitat Liang, J.-J., Suganthan, P. N., Deb, K.: Novel composition test functions for numerical global optimization. In: Paper Presented at the Proceedings 2005 IEEE Swarm Intelligence Symposium, SIS (2005) Liang, J.-J., Suganthan, P. N., Deb, K.: Novel composition test functions for numerical global optimization. In: Paper Presented at the Proceedings 2005 IEEE Swarm Intelligence Symposium, SIS (2005)
58.
Zurück zum Zitat Kaveh, A., Dadras, A., Montazeran, A. H.: Chaotic enhanced colliding bodies algorithms for size optimization of truss structures. Acta Mech. Publishd Online, 1–25 (2019) Kaveh, A., Dadras, A., Montazeran, A. H.: Chaotic enhanced colliding bodies algorithms for size optimization of truss structures. Acta Mech. Publishd Online, 1–25 (2019)
59.
Zurück zum Zitat Kennedy, J., Eberhart, R.: Particle swarm optimization. In: Paper Presented at the Proceedings of IEEE International Conference on Neural Networks (1995) Kennedy, J., Eberhart, R.: Particle swarm optimization. In: Paper Presented at the Proceedings of IEEE International Conference on Neural Networks (1995)
60.
Zurück zum Zitat Mirjalili, S., Mirjalili, S.M., Lewis, A.: Grey wolf optimizer. Adv. Eng. Softw. 69, 46–61 (2014)CrossRef Mirjalili, S., Mirjalili, S.M., Lewis, A.: Grey wolf optimizer. Adv. Eng. Softw. 69, 46–61 (2014)CrossRef
61.
Zurück zum Zitat Storn, R., Price, K.J.: Differential evolution—a simple and efficient heuristic for global optimization over continuous spaces. J. Glob. Optim. 11(4), 341–359 (1997)MathSciNetMATHCrossRef Storn, R., Price, K.J.: Differential evolution—a simple and efficient heuristic for global optimization over continuous spaces. J. Glob. Optim. 11(4), 341–359 (1997)MathSciNetMATHCrossRef
62.
Zurück zum Zitat Yao, X., Liu, Y., Lin, G.: Evolutionary programming made faster. IEEE Trans. Evolut. Comput. 3(2), 82–102 (1999)CrossRef Yao, X., Liu, Y., Lin, G.: Evolutionary programming made faster. IEEE Trans. Evolut. Comput. 3(2), 82–102 (1999)CrossRef
Metadaten
Titel
Quantum evolutionary algorithm with rotational gate and -gate updating in real and integer domains for optimization
verfasst von
M. Kamalinejad
H. Arzani
A. Kaveh
Publikationsdatum
01.06.2019
Verlag
Springer Vienna
Erschienen in
Acta Mechanica / Ausgabe 8/2019
Print ISSN: 0001-5970
Elektronische ISSN: 1619-6937
DOI
https://doi.org/10.1007/s00707-019-02439-2

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