Intuitionistic Fuzzy Sets Studies in Fuzziness and Soft Computing Editor-in-chief Prof. Janusz Kacprzyk Systems Research Institute Polish Academy of Sciences ul. Newelska 6 01-447 Warsaw, Poland E-mail: [email protected] Vol. 3. A. Geyer-Schulz Vol. 14. E. Hisdal Fuzzy Rule-Based Expert Systems and Genetic Logical Structures for Representation Machine Learning. 2nd ed. 1996 of Knowledge and Uncertainty, 1998 ISBN 3-7908-0964-0 ISBN 3-7908-1056-8 Vol. 4. T. Onisawa and J. Kacprzyk (Eds.) Vol. 15. G.J. K1ir and M.J. Wiennan Reliability and Safety Analyses under Uncertainty-Based Information, 1998 Fuzziness. 1995 ISBN 3-7908-1073-8 ISBN 3-7908-0837-7 Vol. 16. D. Driankov and R. Palm (Eds.) Vol. 5. P. Bosc and J. Kacprzyk (Eds.) Advances in Fuzzy Control. 1998 Fuzziness in Database Management ISBN 3-7908-1090-8 Systems. 1995 ISBN 3-7908-0858-X Vol. 17. L. Reznik, V. Dimitrov and Vol. 6. E. S. Lee and Q. Zhu J. Kacprzyk (Eds.) Fuzzy Systems Design. 1998 Fuzzy and Evidence Reasoning. 1995 ISBN 3-7908-1118-1 ISBN 3-7908-0880-6 Vol. 7. B.A. Juliano and W. Bandler Vol. 18. L. Polkowski and A. Skowron (Eds.) Tracing Chains-of-Thought. 1996 Rough Sets in Knowledge Discovery 1. 1998, ISBN 3-7908-1119-X ISBN 3-7908-0922-5 Vol. S. F. Herrera and J. L. Verdegay (Eds.) Vol. 19. L. Polkowski and A. Skowron (Eds.) Genetic Algorithms and Soft Computing. 1996. Rough Sets in Knowledge Discovery 2. 1998. ISBN 3-790S-0956-X ISBN 3-7908-1120-3 Vol. 9. M. Sato et aI. Vol. 20. J. N. Mordeson and P. S. Nair Fuzzy Clustering Models and Applications. 1997, Fuzzy Mathematics. 1998 ISBN 3-7908-1026-6 ISBN 3-7908-1121-1 Vol. 10. L.C. Jain (Ed.) Soft Computing Techniques in Knowledge-based In Vol. 21. L. C. Jain and T. Fukuda (Eds.) telligent Engineering Systems. 1997. Soft Computing for Intelligent Robotic Systems. ISBN 3-790S-1035-5 1998 ISBN 3-7908-1147-5 Vol. II. W. Mielczarski (Ed.) Fuzzy Logic Techniques in Power Systems. 1998, Vol. 22. J. Cardoso and H. Camargo (Eds.) ISBN 3-7908-1044-4 Fuzziness in Petri Nets. 1999 ISBN 3-7908-1158-0 Vol. 12. B. Bouchon-Meunier (Ed.) Aggregation and Fusion of Imperfect Vol. 23. P. S. Szczepaniak (Ed.) Information. 1998 Computational Intelligence and Applications, 1999 ISBN 3-7908-1048-7 ISBN 3-7908-1161-0 Vol. 13. E. Ortowska (Ed.) Incomplete Information: Vol. 24. E. Ortowska (Ed.) Rough Set Analysis. 1998 Logic at Work. 1999 ISBN 3-7908-1049-5 ISBN 3-7908-1164-5 continued on page 324 Krassimir T. Atanassov Intuitionistic Fuzzy Sets Theory and Applications With 121 Figures Springer-Verlag Berlin Heidelberg GmbH Prof. Krassimir T. Atanassov Centre of Biomedical Engineering Bulgarian Academy of Sciences ul. Acad. G. Bonchev, Bl. 105 Sofia-lI13 Bulgaria Email: [email protected] ISBN 978-3-7908-2463-6 Cataloging-in-Publication Data applied for Die Deutsche Bibliothek - CIP-Einheitsaufnabme Atanasov, Krassimir T.: Intuitionistic fuzzy sets: theory and applications I Krassimir T. Atanassov. (Studies in fuzziness and soft computing; Vol. 35) ISBN 978-3-7908-2463-6 ISBN 978-3-7908-1870-3 (eBook) DOI 10.1007/978-3-7908-1870-3 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Berlin Heidelberg GmbH. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1999 Originally published by Physica-Verlag Heidelberg in 1999 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Hardcover Design: Erich Kirchner, Heidelberg SPIN 10733362 88/2202-5 4 3 2 1 0 - Printed on acid-free paper To the three ladies: my mother, my wife, and my daughter. Foreword In the beginning of 1983, I came across A. Kaufmann's book "Introduction to the theory of fuzzy sets" (Academic Press, New York, 1975). This was my first acquaintance with the fuzzy set theory. Then I tried to introduce a new component (which determines the degree of non-membership) in the definition of these sets and to study the properties of the new objects so defined. I defined ordinary operations as "n", "U", "+" and "." over the new sets, but I had began to look more seriously at them since April 1983, when I defined operators analogous to the modal operators of "necessity" and "possibility". The late George Gargov (7 April 1947 - 9 November 1996) is the "god father" of the sets I introduced - in fact, he has invented the name "intu itionistic fuzzy", motivated by the fact that the law of the excluded middle does not hold for them. Presently, intuitionistic fuzzy sets are an object of intensive research by scholars and scientists from over ten countries. This book is the first attempt for a more comprehensive and complete report on the intuitionistic fuzzy set theory and its more relevant applications in a variety of diverse fields. In this sense, it has also a referential character. Naturally, the theory is far from being complete, there are some gaps and still unsolved, open questions and problems - some of them are formu lated at the end of the book. A solution to any of them would stimulate the development of the intuitionistic fuzzy set theory, and contribute to fruitful applications. April, 1999 Krassimir T. Atanassov Sofia, Bulgaria Acknowledgements First of all, I wish to convey my most sincere gratitude to all of my Bul garian co-authors and collaborators, especially to Hristo Aladjov, Plamen Angelov, Ognian Asparoukhov, Lilija Atanassova, Stefan Danchev, Dinko Dimitrov, Peter Georgiev, Stefan Hadjitodorov, Lubomir Hadjyisky, Ludmila Kuncheva, Dimiter Lakov, Nikolai Nikolov, Valentina Radeva, Dimiter Sas selov, Joseph Sorsich, Stefka Stoeva and Darinka Stoyanova, Peter Vassilev, for their active participation and collaboration in developing the intuitionistic fuzzy set theory. Anthony Shannon (Australia), Christer Carlsson (Sweden), Didier Dubois and Henri Prade (France), Siegfried Gottwald and Hans-Jiirgen Zimmer mann (Germany), Humberto Bustince Sola, Pedro Burillo Lopez, Victoria Mohedano, Ana Burusco and R. Fuentes-Gonzalez (Spain), Eulalia Szmidt, Tadeusz Gerstenkorn and Jacek Manko (Poland), Toader Buhaescu (Ro mania), Dogan Coker, Es Haydar, Sadik Bayhan, Ibrahim Ibrahimoglu and Mustafa Demirci (Turkey), Hung T. Nguyen, Misha Koshelev, Vladik Krei novich, Bhuvan Rachamreddy, Cecilia Temponi, Haris Yasemis (USA), Berlin Wu (Taiwan), Soon-Ki Kim and Young Hyun Kim (S. Korea), Tuyun Chen, Li Zou, Zhang Cheng, YauaXue-hai and Yin Guo-min (P.R. of China), Ranjit Biswas, Srijit Biswas, Kankana Chakrabarty, K. C. Chattopadhyay, Supriya Kumar De, Tapas Kumar Mondal, U. K. Mukherjee, Sudarsan Nanda, Akhil Ranjan Roy and S. K. Samanta (India), and T. E. Kaminsky (Russia) deserve my thanks for their very important research on intuitionistic fuzzy sets and for a moral support I received from them. Special thanks are due to Janusz Kacprzyk (Poland), the editor-in-chief of this book series, who urged me to finalise my several-year-Iong work on the theory and applications of intuitionistic fuzzy sets, and to prepare this book. My friends and post-graduate students Nikolai Nikolov, Peter Georgiev and Valentina Radeva, whose knowledge and dedication have helped attain a professional camera-ready form of the book, deserve my deep thanks and appreciation. x I wish to thank Dr. Martina Bihn and Mrs. Gabriele Keidel from Physica Verlag (A Springer-Verlag Company), Heidelberg and New York, for their kind consideration and help in arranging and running this book publication project. And last but not least, I would like to thank the three most important ladies in my life: my mother, my wife, and my daughter, who have been encouraging and stimulating all my scientific research. April, 1999 Krassimir T. Atanassov Sofia, Bulgaria Intuitionistic Fuzzy Sets: Past and Present Present-day science and technology is featured with complex processes and phenomena for which complete information is not always available. For such cases, mathematical models are developed to handle various types of systems containing elements of uncertainty. A large part of these models are based on a recent extension of the ordinary set theory, namely, the so-called fuzzy sets. Fuzzy sets (FSs, for short) were introduced by L.A. Zadeh [507] in 1965. The interest in this theory is constantly rising, which is proved by an in creasing number of publications devoted to the field. Twenty years ago, for example, according to some estimations, there have been about 500 publi cations, while 10 years after their number was as large as 5000. Today it is hard to estimate even the approximate number of research works related to the fuzzy sets theory. Two years after the emergence of the concept of a fuzzy set, it was generalized by J. Goguen in [297] who proposed L-fuzzy sets. Currently there are also some other extensions of FSs, and the aim of this book is to present and discuss one of them. One generalisation of the notion of FS was proposed by the author of this book in the beginning of 1983. To some extent, it began as a mathematical game, inspired by the Russian translation of "Introduction to the theory of fuzzy sets" by A. Kaufmann [324]. In May 1983 it turned out that the new sets allow the definition of operators which are, in a sense, analogous to the modal ones (in the case of ordinary fuzzy sets such operators are meaningless, since they reduce to identity). It was then that the author realized that he had found a promising direction of research and published the results in [20]. George Gargov not only gave the new sets their name, intuitionistic fuzzy sets (IFSs, for short), as their fuzzification denies the law of the excluded middle, one of the main ideas of intuitionism, but also encouraged the author to continue his work on them. XII Later, with Stefka Stoeva we further generalized that concept to an intu itionistic L-fuzzy set [117] (see Section 3.1), where L stands for some lattice coupled with a special negation. Together with Lilija Atanassova we gave an example [123] of a genuine IFS (an IFS which is not a fuzzy set) (see Section 1.1). An analogous example for intuitionistic L-fuzzy sets is given in [26] (see Section 3.1). Some basic results on the IFSs were published in [21, 24, 25, 28, 40, 46, 50, 52, 56, 57, 58, 59, 60, 116, 119]. Various operators were defined on the IFSs, which are analogous to the modal logic operators [28, 29, 32, 36, 50, 51, 53, 55, 74, 75] (see Chapter 1). A further generalisation of the IFSs, the interval-valued IFSs (IVIFSs, for short) is introduced in [28,61,106] and George Gargov and the author showed that interval valued fuzzy sets are equivalent to IFSs [106] (see Chapter 2). A geometric interpretation of an IFS was given [31] (see Chapter 1). Temporal IFSs were introduced in [42] (see Section 3.3). A second type of IFSs (see Section 3.4) is introduced in [47], IFSs over an universe which in turn is an IFS over another universe are described in [38] (see Section 1.15). Elements Qf intuitionistic fuzzy logic (IFL, for short): two versions of intuitionistic fuzzy propositional calculus, intuitionistic fuzzy predicate calcu lus, two versions of intuitionistic fuzzy modal logic, and temporal intuitionistic fuzzy logic (TIFL, for short) were defined and investigated in a series of com munications [30, 34, 107, 275] (the last two together with George Gargov). These results will be published in the present book. Versions of FORTRAN, C, and PASCAL software packages implement ing operations, relations and operators over the IFSs are introduced. In the area of applications we have investigated the so-called V -fuzzy Petri nets, reduced V -fuzzy generalized nets [442], intuitionistic fuzzy gener alized nets of type I [23] and II [41, 90] (see Section 4.1) and intuitionistic fuzzy programs (with Stefka Stoeva) [118]. A gravity field of many bodies (with Dimitar Sasselov) is announced in [428]. Intuitionistic fuzzy models of neural networks (with Lubomir Hadjyisky [306, 307]) were developed on the basis of IFSs. Intuitionistic fuzzy expert systems [54, 62, 63, 411, 412] (see Section 4.3), intuitionistic fuzzy systems [68] (see Section 4.5), intuitionistic fuzzy PROLOG [110, 111, 283] and intuitionistic fuzzy constraint logic pro gramming [45, 49] were developed, too. The last two topics will be included in a next book. Some new results on the IFS theory and its applications were reported to the "Mathematical Foundation of Artificial Intelligence" Seminars held in Sofia in October, 1989 [33, 274, 283, 308], March, 1990 [37, 38, 109, 282, 445,449]' June, 1990 [446,447]' November, 1990 [39,448] and October, 1994 [67,77,160,162,176]. In the beginning of the 1990s, research on IFSs was reported outside Bulgaria: in Romania - by Toader Buhaescu [150, 151, 152, 153], in Poland - by Tadeusz Gerstenkorn and Jacek Manko [290, 291, 292, 293, 294, 295, 367,