Memorial to Professor Wataru Takahashi

Professor Wataru Takahashi
(January 22, 1944 - November 19, 2020)

Professor Wataru Takahashi passed away on November 19, 2020, at the age of 76. Professor Takahashi was born in Tokyo in 1944. After graduating from the Department of Mathematics of Yokohama National University, he entered the Graduate school of Tokyo Institute of Technology in April 1966. He studied Functional Analysis and received his Doctorate of Science degree in 1971, under his supervisor Professor H. Umegaki. He gained a position as an Assistant Professor in the Department of Information Science in Tokyo Institute of Technology in April 1971, and as an Associate Professor in the Faculty of Education at Yokohama National University in April 1972. After two years of teaching there, he came back to Tokyo Institute of Technology as an Associate Professor in 1974. He was promoted to a Professor in the department in July 1999.

His research covers a large number of topics in Nonlinear Analysis. The outstanding successes among his many achievements are as follows: nonlinear ergodic theory for nonexpansive semigroups, fixed point theorems for nonlinear mappings, studies of convex metric spaces, the approximation of fixed points by various types of methods, and others. He wrote more than 500 academic papers related to these topics, and many mathematical articles have cited his works over 10,000 times. Besides the publication of his works, Professor Takahashi made a significant contribution to academic society through editorial activities in international journals. He is one of the founding editors of the Journal of Nonlinear and Convex Analysis, founded in 2000, the leading journals in this field. His name is on the list of the editorial board of various journals.

He was also one of the prominent founding members of two conference series: International Conference on Nonlinear Analysis and Convex Analysis (NACA) and Asian conference on Nonlinear Analysis and Optimization (NAO-Asia). The latest 11th NACA conference took place in Hakodate, Hokkaido, Japan, on August 2019, as the celebrated joint conference with the International Conference on Optimization: Techniques and Applications (ICOTA). At this conference, they held a special celebrating session for Professor Wataru Takahashi on his 75th birthday.

Professor Takahashi was also a successful educator. Forty-three students obtained their Ph.D. degrees under his supervision. Most of them have been working on the research of mathematics in the academic field.

We now convey our sincere condolences on our great professor's passing.


On behalf of his students, we are very sorry to announce the sad news that Professor Wataru Takahashi passed away on November 19, 2020.

Many people dearly remember Wataru of our group for his significant contributions to a great number of topics of Nonlinear Analysis, and for a successful educator with the number of students who obtained their Ph.D. degrees under his supervision.

He also organized many international conferences related to Nonlinear Analysis, Convex Analysis and Optimization; he founded the International Conference on Nonlinear Analysis and Convex Analysis (NACA) starting from the first one in Niigata, Japan, in 1998. Last year (2019), the 11th took place jointly with the International Conference on Optimization: Techniques and Applications (ICOTA) in Future University Hakodate, Japan, in August of 2019.

He gave us many suggestions and advice several times. We remember his personality and activity forever through his intellectually and strongly inquiring minds.

He had more than 100 coauthors during his long scientific career. We will always be grateful to him for his suggestion, guidance, and friendship, and we are sure that many others feel the same.

We will honor the memory of Prof. Wataru Takahashi in various opportunities. As a first step, we created a memorial page where the members who wish to express their thoughts and condolences may do so.

If you would like to post a contribution on this page, please send a message to Your contribution will appear in 2-3 days.

Sincerely yours,

Norimichi Hirano
Koichiro Naito
Naoki Shioji
Yasunori Kimura

Words of condolence

I am really sorry and sad to hear the news. As you know, he was a great mathematician, and for me, he was a great educator. During a period when I was a student in his laboratory, I visited his office almost every day and asked some questions. He kindly answered my questions without looking irritated. I still remember one of my questions. I asked about the definition of isometric isomorphism between two normed linear spaces. As you know, isomorphic isomorphism appears in many places. At that time, I did not understand the essence of isomorphic isomorphisms for mathematical structures. He answered my question as follows. First, he explained the isomorphic isomorphism between two sets. Next, for groups, for graphs, for topological spaces, and I caught the essence. I had a deep emotion for his good teaching.

Naoki Shioji (2020/12/04)

I am deeply sad about the news that Professor Takahashi passed away on 19 November 2020. I met Professor Takahashi first at ICFPTA 2015 meeting in Istanbul, personally. I knew him but did not meet face to face before. He was one of the plenary speakers of the ICFPTA2015. As it is expected, such great mathematicians are very humble and very kind. One of the best examples was Prof. Wataru Takahashi. I was appointed as the chair of his talk. I searched for his academic success to present and invite him for giving his talk. When I saw the search results, my admiration had grown a thousandfold. Most famous and leading mathematicians do not spare time to train students. But Professor Takahashi has graduated around 40 doctoral students, most of whom have proven themselves in the academic world. Besides, his contribution to science by establishing academic journals is also very important and valuable. Considering that very few famous mathematicians are so versatile, I see that he is not only a good researcher and a very good scientist, but also a very devoted person. I have always admired him and will remember him with respect.

Erdal Karapinar (2020/12/04)

Professor W. Takahashi was an icon in the area of fixed point theory and in mathematics at large, with the vast academic research publications and student trained, he will never be forgotten. I was privileged to have met him in Thailand and Japan in two conferences of nonlinear analysis and optimization, we had some discussion together and have learnt from his vast experience during his presentation and our discussion. May his soul rest in peace.

Umar Batsari Yusuf (Hassan Usman Katsina Polytechnic, Nigeria) (2020/12/04)



本日 (12/4) 研究集会があり,共通不動点定理に関する発表を行いました.発表の冒頭で函館でのシンポジウムの集合写真を提示しながら,渉先生がご逝去されたことを参加者にお伝えした次第です.また,10年ほど前に頂戴したお言葉「不動点定理で分離定理を証明できるんだよ.」の延長上に本日の発表があることに天与のご縁を感じております.謹んで高橋渉先生のご冥福をお祈り申し上げます.

九州大学 川崎英文 (2020/12/04)

I am very sad and sorry to hear that Wataru-sensei has passed away. This is terrible news.

Wataru-sensei was an excellent mathematician, a remarkable teacher and mentor, and an outstanding human being. I will always remember him with the greatest admiration and esteem. My wife and I will never forget Wataru-sensei's most kind hospitality when we visited him at Tokodai.

His passing is a great loss for the mathematical community and, in particular, for those of us working in the areas of Nonlinear Functional Analysis and Fixed Point Theory, in which Wataru was one of the leading contributors for decades. He will always be remembered as an outstanding researcher, an excellent advisor of dozens of successful students, and a good friend. We very much appreciate his support for PAFA, where he published several important papers. The journals founded and edited by Wataru, as well as the numerous conferences he organized, have played, and continue to play a significant role for all the members of our community.

We are sending our heartfelt condolences to Wataru-sensei's family.

Simeon Reich (2020/12/05)

To Professor Wataru Takahashi, my good mentor and friend!

One of the great mathematicians who was very kind to young students and me. His deep results in mathematics inspire us but it is still very hard to follow all his steps. For me, I always tried to find out how he discovered and invented so many new concepts and methods in the old time which are still being followed nowadays. NACA-ICOTA (August 2019) Conference at Hakodate was the last time we met. Life is too short for you as you still showed me in our last conversation that lots of papers are waiting to come out. Rest in Peace my SENSEI.

Sompong Dhompongsa (2020/12/05)

About 25 years ago, I was knocking on the lab door of Professor Takahashi to study some problems related to image recovery with a functional analysis approach. In those days, I was struggling with signal processing problems based on real data and feeling the weakness of my theoretical background. Although I could not accomplish this purpose, (I have changed direction of my study to differential equation oriented for some reason), I truly feel some qualitative change has occurred in myself before Takahashi sensei and after Takahashi sensei. May rest in peace, Takahashi sensei.

Kohtaro Watanabe (2020/12/07)






滋賀大学経済学部 近藤豊将 (2020/12/07)

I am sad to hear the bad news. Prof. Takahashi was a respectful professor. He was always very kind to people.

One year, I sent two of my Ph.D. students to a conference organized by Prof. Takahashi or his students. These two students of mine were inexperienced and first time abroad. Prof. Takahashi attended their talks and encouraged them. This moved me. Please send my condolence to Prof. Takahashi's family.

Liqun Qi (2020/12/09)




秋田県立大学 荒谷洋輔 (2020/12/10)

I am very sad about the news that Professor Wataru Takahashi passed away on 19 November.

He was a great mathematician. I met him first at Tokyo and also in conferences he organized, NACA-ICOTA (August 2019) Conference at Hakodate was the last time we met.

We have had a long and deep cooperation.

Charles Castaing (2020/12/10)

I am very sad about the news that Professor Takahashi passed away on 19 November 2020.

When I was a PHD student, I attended the meeting NACA at Chitose with my classmate. That was the first time and the last time we met Professor Takahashi. He was very nice to us and even joined our session when we gave our talks. We were very grateful to Professor Takahashi for encouraging us.

May rest in peace, Professor Takahashi.

Chang Jingya (2020/12/10)

Dear Family and Friends of Professor Takahashi:

Please accept our sincere condolences to all of you on this sad event. He was a very nice friend, teacher, and father. He did a great contribution for the mathematical community. He will remain in our heart forever.

Sehie Park (2020/12/11)

The passing of Wataru Takahashi is a huge loss to the mathematical world. Beyond his numerous academic contributions, he created an international network of researchers that brought together people from many countries and provided them new ways to communicate and publish their work.

The cycles of meetings he started up have been a scientific benefit and source of yearly travel pleasure for very many of us, and for me particularly. Without them and his kind invitations, I would not have learned to know so many colleagues in Asia and to love so much the culture of Japan and its neighbors. I will greatly miss him and his influential efforts.

Terry Rockafellar (2020/12/12)

I would like to thank Wataru for his many years of collaborations and friendship since 1969, when I started reading his first paper: Fixed point theorem for amenable semigroup of nonexpansive mappings. Kōdai Math. Sem. Rep. 21 (1969), 383–386 close to my early work. Since then we have met and worked together for many years in Canada and Japan. Wataru has a truly wonderful personality, warm, generous and helpful.

A. T. Lau (2020/12/12)

I am deeply sad to hear the news, and I want to express my sincere gratitude for Prof. Wataru TAKAHASHI. I met him first time at his lecture in my 2nd year of Tokyo Institute of Technology, bachelor course. I was quite impressed by his elegant mathematics and his messages to us. He often repeated, “Go your way” and “Believe your ability.” At the last year of my bachelor course, I began to study mathematics under his supervision. As I wanted to learn from him more, I decided to go to master course. It was valuable 3 years for me that I could learn under him. After my accomplishment of master course, I began to work at financial world and keep working there over 20 years. After my departure from his laboratory, I faced various difficulties both in my job and in my private life. At those cases, I always remembered his teachings and overcame many difficulties. I will probably face other difficulties in my life, but I will overcome them with his heartful messages. I am proud that I was a member of his laboratory, and he is still alive in my mind.

Keiichi Inoue (2020/12/12)

I would like to present my sincere condolences to the passing-away of Professor Wataru Takahashi. He was very important and excellent scholar at the area of convex analysis and nonlinear analysis. He wrote very important papers and books for convex and nonlinear analysis. He organized so nice and important conferences for convex and nonlinear analysis. He made great contributions for the mathematics society in the world.

Gue Myung Lee (2020/12/15)

I would like to express my sincere condolences to Professor Wataru Takahashi. I vividly remember his class of Functional Analysis a little less than fifty years ago at Tokyo Institute of Technology. He was an excellent teacher in addition to a distinguished scholar. His lecture was clear and easy to understand, which shows his unusual talent of understanding mathematics and his fine and gentle character. Many mathematical economists as well as mathematicians had been encouraged by his lectures.

Hidetoshi Komiya (2020/12/15)

I was deeply shocked when I heard the sudden news. The passing of Professor Wataru Takahashi is a huge loss to us. He created and worked so hard for international conferences like RIMS-NACA, NACA(-ICOTA) and NAO-Asia. Particularly for me, he always encouraged and supported me in many aspects. He will be alive in my mind forever.

Do Sang Kim (2020/12/15)

I would like to express my deep condolences to Professor Wataru Takahashi’s family and friends.

It was 1999, that I wrote the first letter to Professor Takahashi and asked him for suggestions on the struggling in my research, and he kindly introduced me the book written by him. The book and many others books under his name are very helpful to my works, thereafter. Years after our first contact, he made the first visit to my university, Chulalongkorn University in Bangkok, gave lecture to participants from many universities in the country. Since then, many Thai PhD students had worked under his supervision. As a very kind teacher and a beloved friend he will be in my heart forever.

Imchit Termwuttipong (2020/12/15)







小宮清孝 (2020/12/15)

I am most upset and sorry to hear that Professor Wataru Takahashi has passed. The news of his sudden death is a terrible shock.

I would like to express my deepest condolence to the passing away of Professor Wataru Takahashi.

I remember him with great affection and respect. Especially, I cannot forget his hospitality and considerateness during a stay at Tokyo Institute of Technology in 1990 along with his kind advices and collaborations for my researches.

Both as a remarkable teacher and as a distinguished scholar, he is irreplaceable. His passing is a huge loss to all of us. He will remain in my mind forever.

Jong Soo Jung (2020/12/16)

I really can't hold back the shock and sadness after hearing the news that Prof. Wataru Takahashi passed away. He is a friend who has kept my friendship for 40 years since my first meeting. In this time, With all my heart, In this time, I wish to express to have rest in peace, Prof. Wataru Takahashi.

Jong Kyu Kim (2020/12/17)

I respectfully express my sincere condolences to Professor Wataru Takahashi. Since 2002, I could often meet him with his students in the conferences NACA, NAO and NFAA, with his great contribution to the mathematical community. I will remember him with a gentle smile. May his soul rest in peace.

In-Sook Kim (2020/12/17)

It was a great shock to me to hear his passing away. In my deep memory, he is still breathing, making a smile in Heaven, saying "I am happy. Bye for now!", following a string of bright light, listening angel's whispering.

I wish you will be now .... calm and peaceful, with my hearty condolence.

Taehwa Kim (2020/12/17)

It is indeed a very sad news that Professor Wataru Takahashi passed away on November 19, 2020.

Professor Wataru Takahashi was for me not only an excellent mathematician and a wonderful model to follow, but also a very important friend. I learned a lot from his books and papers, as well as from many instructive discussions in NSYSU Kaohsiung, Taiwan.

Moreover, Professor Wataru Takahashi had a very important contribution for the development and the success of the journal FIXED POINT THEORY, for which he served as a member of the Editorial Board for more than 17 years.

His death is a huge lost for the math community and for all those who are working in the field of Nonlinear and Convex Analysis.

On behalf of the research group in Nonlinear Analysis from Babes-Bolyai University Cluj-Napoca, Romania we are sending our heartfelt condolences to his family.

Adrian Petrusel (2020/12/19)

It is sad. I knew Wataru for close to 50 years. We first met in Berkeley, California. At a party I saw young Japanese fellow sitting alone and looking shy. I approached him, talked to, and very soon we drank our first drink. It was the beginning of a long-standing friendship. We met many times in many places all over the world. I visited him 18 times in Japan. I owe him a lot. He taught me japanese style of life and let me love it. Farewell Wataru, farewell.

Condolences to all: family, students and friends.

Kazimierz (Kaz) Goebel (2020/12/19)

Professor Wataru Takahashi has been known to me for a long time as an expert of nonlinear and convex analysis, and I actually had occasional email correspondences with him for many years, but it was only recently that I had the chance to talk to him personally. In 2018 I was invited to give a talk at the 6th conference of NAO-Asia in Okinawa on some work on discrete optimization related to convexity. In NAO-Asia 2018, it was impressive for me to witness an international community of nonlinear analysis that Professor Takahashi developed with enthusiasm and friendship. Not only elderly established researchers but younger people also enjoyed the friendly conference with substantial scientific interaction.

On top of his numerous mathematical papers and books, his contribution to forming an international community, especially in Asia, is outstanding. I am really sorry for the loss of such an international leader, and I can only hope that his enthusiasm will be inherited by his successors.

Kazuo Murota (2020/12/20)

With deep sadness we have heard that Prof. Wataru Takahashi passed away. Prof. Wataru Takahashi was an outstanding mathematician, an exceptional human being, a very good colleague and a wonderful friend. We will miss him sorely.

Christiane Tammer and Elisabeth Köbis (2020/12/20)

Learning that Wataru Takahashi passed away caused a great pain in my heart. Actually, since more than 25 years, he was one of my best friends in the mathematical community. He was a great mathematician, a great teacher and an extraordinarily fine man. I will remember him for ever.

Biagio Ricceri (2020/12/21)

In deep mourning for Professor Wataru Takahashi, I remember the days at Yokohama National University when he was 28 and I was 20. I am sincerely grateful that I was able to meet him. And I appreciate Professor Wataru Takahashi all the kindness he has shown me for about a half century. May his soul rest in peace.

Yukio Takeuchi (2020/12/22)

It was a great shock to me to hear the news that Professor Wataru Takahashi passed away. I met Professor Wataru Takahashi for more than 25 years. Every year, I met him several times in the international conferences on fixed point theory, nonlinear and convex analysis. He was an outstanding mathematician in the world, a great teacher, I and my students learned a lot from his books, papers, lectures, and his visiting to our university. Professor Wataru Takahashi organized many international conference on nonlinear and convex analysis and optimization. He has great contribution to the development of these fields and mathematical community.

Lai-Jiu Lin (2020/12/22)

When I heard the sad news from my supervisor Professor Do Sang Kim, I was deeply shocked and I almost can not believe this (even now). I still remembered the moment when I opened his photo in my slide and started to introduce him (in IWNAO, Korea, August 6-8, 2018), Professor Wataru Takahashi looked at me with his kind smiles as if it was yesterday....

Professor Wataru Takahashi is so mild and kind for young researchers like me. He also once sent his recommendation letter for helping me to find my job. I will always remember his kindness and encouragement! May rest in peace.

Liguo Jiao (2020/12/23)

The loss of Prof. Takahashi is deeply felt not only by his family and his students. The whole mathematical community has lost a very important point of reference.

Giuseppe Marino (2020/12/23)

I was exposed to the sudden news, and with deep sorrow, I just lost words. Professor Takahashi was a great Mathematician throughout his whole life. I would like to take what I learned from you over. My deepest sympathy.

Shigeru Iemoto (2020/12/28)



北海道大学名誉教授 安藤毅 (2020/12/31)

In the passing away of Professor W. Takahashi, we have lost a prominent worker in the area of Fixed Point Theory. His death is indeed a great loss to the field of mathematics. Our heartfelt condolences to his bereaved family members and admirers. May the departed soul rest in peace. Om Shanti.

Ravindra K Bisht (2021/01/01)

Dear Family and Friends of Professor Wataru Takahashi,

Please accept my deepest condolences for your loss. Professor Wataru Takahashi was a great mathematician/researcher, we will all miss him. He is at peace. Sincerely,

Issam Dali (2021/01/14)

I have been in deep sorrow since Professor Wataru Takahashi passed away. He is a great teacher and mentor of mathematics and life for me. The first time I attended an international conference when I was a student was at NACA cycle meeting he launched. As you know, he created an international network of researchers that brought together people from many countries and provided them new ways to communicate and publish their work. I am one of his students who continue to benefit from the wonderful relationship he has created. I am grateful for his many kindnesses, encouragement and affection that cannot be expressed in words. I also would like to pass his spirit down the next generations.

Mayumi Hojo (2021/01/08)

Dr. Professor Wataru Takahashi was a famous mathematician around the whole world. He was a great researcher, educator and leader in the field of nonlinear analysis and its applications. His numerous publications, including books, research papers, and so forth, provided numerous new results and very useful techniques in nonlinear analysis and related fields. Under his leadership, several international journals and some international conferences have grown in importance throughout the world. Dr. Professor Wataru Takahashi made exceptional contributions of enduring importance to the development of the field of nonlinear analysis.

We will remember Dr. Professor Wataru Takahashi forever.

Jinlu Li (2021/01/08)


山形大学名誉教授、数学・ゲーム工房広報部長 高橋眞映 (2021/01/08)

Dear Family and Friends of Professor Wataru Takahashi,

I am so sorry that Professor Wataru Takahashi passed away. I will never forget the NACA and NAO conferences organized in Japan, Korea, Thailand,… where I met him. He is a great man and will forever be in my heart. Great memories will live on.

Ta Quang Son (2021/01/08)

Dear Professor W. Takahashi's family,

Just I heard sad news from Prof. Jong Kyu Kim. I am very sorry to hear that Prof. W. Takahashi passed away on November 19, 2020. Please, accept our sincere condolences on this sad event. He was a great mathematician, our teacher and our friend. He contributed greatly to Nonlinear Analysis, especially, Fixed Point Theory and Applications. Prof. W. Takahashi's great achievements will remain in our heart forever.

Yeol Je Cho (20201/01/08)

I would like to express my deepest sympathy on the passing of Professor Wataru Takahashi. He was a truly great professor and we are proud to have received his guidance. Please convey my sincerest condolences to his family.

Jun Kawabe (2021/01/08)

Dear Colleagues and Friends,

I am very sad that Professor Wataru Takahashi passed away on November 19, 2020, at the age of 76. Professor Wataru Takahashi was a prominent mathematician and a nice person. I attended a number of his influential and encouraging lectures in Korea, Taiwan, and Thailand. Thanks to his kind invitation and generous financial support, I had a chance to participate in The Sixth International Conference on Nonlinear Analysis and Convex Analysis (March 27-31, 2009), Tokyo Institute of Technology, Tokyo, Japan. I always remember him and his wonderful images.

Please send my deep condolences to his Family, colleagues, and students.

Nguyen Dong Yen (Institute of Mathematics, Vietnam Academy of Science and Technology, Hanoi, Vietnam) (2021/01/08)

Memorial to Professor Wataru Takahashi:

I was sorry and grieved to hear that Professor Wataru Takahashi passed away last November. No words can express the deep sadness we feel. My wife and I were very shocked to hear of Professor Wataru Takahashi's news. We will always remember him with great affection and very proudly. We hope and pray Professor Wataru Takahashi will rest in peace and comfort in heaven!

We are sending our deepest condolences and we hope and pray that Professor Wataru Takahashi's family will soon find comfort in this time of sorrow.

Young-Ho Kim (2021/01/08)

We express our deepest condolences for Professor Professor Wataru Takahashi's death and wish you a restful life in the comfort of heaven.

Taekyun Kim (2021/01/08)

高橋渉先生におかれましては喜寿のお祝いのお知らせがある頃かと思っておりました。 ご逝去の報に接し、謹んでお悔やみ申し上げますとともに、心からご冥福をお祈りいたします。私は、専門分野も少し異なり、先生との直接の関係はないのですが、色々な場面でチャンスを与えて頂きありがたいことと思っておりました。安らかにご永眠されますよう心よりお祈りいたします。

古谷希世子 (FURUYA Kiyoko) (2021/01/09)

We are all shocked and sad to learn that our beloved Professor Wataru Takahashi left us so soon and so sudden at November 19, 2020.

Wataru had been an Honorary Chair Professor of our Department of Applied Mathematics, National Sun Yat-sen University, Kaohsiung, Taiwan, for about 10 years. Among his 524 publications found in Mathscinet, there are 17 papers coauthored with me, 70 papers addressed to our department, and about 200 papers joined with colleagues in Taiwan. It is never overemphasized how important the contribution Wataru made to the field of analysis in Taiwan.

We are in deep sorrow in the loss of our best friend, best colleague, and best teacher, Wataru Takahashi Sensei.

May Sensei rest in peace.

Ngai-Ching Wong 黃毅青 (2021/01/09)


山田功 (Isao YAMADA) (2021/01/09)

Dear Prof. Dr. and great team.

I would love to share with you my great regret and my sadness for the loss of our great professor, Prof. Dr. Wataru Takahashi. He was a distinguished professor and great scholar who did not fail to help a student all the time. Always encouraging, motivating and cooperating with them, and participating in their research hand in hand, and on the other hand, he was a first class social person.

I have attended multiple science sessions, seminars, symposiums, and workshops for more than two years in Prof. Dr. Wataru Takahashi Laboratory at the Tokyo Institute of Technology. Our esteemed professor used to present and supervise it with the aim of advancing and raising the level of his students. On the other side, he gave me many opportunities to attend and participate some joint research papers with the wonderful scientific community all over the world, via some international conferences of Convex and Nonlinear analysis.

I was fortunate because he supervised my PhD thesis through the scientific channel between Egypt and Japan, and I also had the opportunity to bring him to Egypt and give two of the most amazing lectures that I have heard in my life in the Mathematics Department, Faculty of Science, Ain Shams University in 2002.

I was also fortunate to be able to discuss my PhD thesis in the existence of him personally with his continuous encouragement of my continued construction. May God have mercy on him and spacious entrance.

Sahar Mohamed Ali Abou Bakr (2021/01/09)




松井泰子 (Yasuko Matsui) (2021/01/12)

I first met Professor Wataru Takahashi at Tokyo Institute of Technology in 2009 attending an International Conference on Fixed point Theory and Optimizations organized by him and his colleagues. He has immensely inspired and motivated me a lot in doing many mathematical researches. He was certainly one of the great Mathematicians I have ever known and he will be forever in my memories. When I heard the sad news, I was incredibly shocked. We never really think that those so near and dear to us will really pass, so I know this must be especially hard on his family and students, and I can’t imagine what they’re going through. While there’s nothing I can do to change what happened, I can continue to offer you my love. Extending my most heartfelt condolences to all his friends and his family.

Jamnian Nantadilok (2021/01/12)

Dear Family and Friends of Professor Takahashi,

I was very sad when I heard the death of Professor Takahashi. Professor Takahashi was a famous mathematician around the whole world. I carefully read many papers of Professor Takahashi on the fixed point theory and its applications when I entered this field. Professor Takahashi had introduced new things and guided the development of the fixed point theory and its applications.

Qiao-Li Dong (2021/01/13)



宮下弘 (2021/1/13)

This is very sad news. Besides being a great mathematician and educator, Professor Wataru Takahashi was a great gentleman. It is thanks to him that I made several visits to Japan for the NACA and NAO conferences, and discovered the wonderful culture of this country. He was so welcoming. I will remember him forever.

Marc Lassonde (2021/01/15)

I am very surprised by the sad news. I would like to express my sincere condolences to his family and friends. Now, I understand that I have to keep going ahead by studying and teaching mathematics with his strong and kind spirits in my mind. I would like to express my gratitude to Professor Wataru Takahashi again in this occasion for his constant encouragement given to me so far.

It was a day in the summer of 1998 when I first met Professor Wataru Takahashi in front of his office in Tokyo Institute of Technology. I was very pleased to know that he had kindly accepted me to be a graduate student in his laboratory from April of 1999. On that day I was so attracted by his personality and his strong kindness that I felt happiness in my heart very much. When I saw a long queue of graduate students with papers and notebooks in their hands waiting for him, I understood that he had many graduate students attracted by his positive minds and strong abilities.

The last time when I made a conversation with Professor Wataru Takahashi became July 28 of 2020. On the day I made a telephone call to his home in order to discuss something with him. He said to me with his strong voice on the phone, "You can do it. Don't be afraid of anything. You have many friends to help you. Everything's gonna be alright". I said to him back, "Thank you very much, Takahashi-sensei. I will do my best". I was very glad to talk to him because his voice messages made me feel stronger. At that moment I couldn't imagine that the conversation would be my last conversation with him.

Since the first meeting with him in 1998, Professor Wataru Takahashi had let me know many useful words and phrases related to mathematics and our lives. Let me reminds me some of them as follows.

(1) Enjoy studying mathematics; (2) Mathematics is interesting since we study it together; (3) Try to prove a well known theorem in mathematics with your pen and notebook and without any textbook; (4) You had better stop studying mathematics on a day if you feel like studying more. Then you can continue your study in the following day; (5) You would understand that every experience had a meaning to your life; (6) You can do it.

Arigatou Gozaimasu so much always, Takahashi-sensei. Since you will always be in my mind clearly, obviously, and strongly, I am with you everyday:-)

Fumiaki Kohsaka (2021/01/15)

It was very sad news to hear that Prof. Wataru Takahashi passed away on November 19, 2020. It made me feel stunned for a while and followed with sadness. I met him for the first time at Chulalongkorn University around 2005, at that time I was a PhD student in mathematics from Naresuan University under my supervisor Prof. Somyot Plubtieng. I had the opportunity to do research in Japan with Prof. Wataru Takahashi in 2006-2007 for 4 months and was warmly welcomed by Prof. Wataru Takahashi, Madam Yoko Tahahshi, Toshi Takahashi and his students. Over the course of four months, he has provided a very useful research guide, where I have absorbed a lot of diligent work experience. I met many new Japanese friends who were his students, who were very helpful during my time at the Tokyo Institute of Technology. In my view, Prof. Wataru Takahashi was a great mathematician, hardworking and very focused on research, which inspired and set a good role model for me in my work. His research papers have appeared in many journals and have played a significant role in the development of mathematical research around the world, and I am a mathematician who loves to study and develop research in his direction. In my personal opinion, he is like the father who guides and teaches us to success. Finally, I would like to express my deepest condolences to his family, his students and his friends on the passing of Prof. Wataru Takahashi. He will be the inspiration to all mathematicians and will be forever in my heart and my memories.

Kasamsuk Ungchittrakool (2021/01/17)

I am very sad and sorry to hear about the death of Professor Takahashi. The mathematical community has lost a creator and a wise person like Prof. Takahashi forever. My research is in the field of fixed point theory and applications, and Professor Takahashi made breakthroughs and contributions in this field. When I entered this field, I read many of Prof. Takahashi's articles, such as his work on hybrid and shrinking projections, which have been continuously studied and researched by many scholars. I regret very much that I did not meet Prof. Takahashi. Prof. Takahashi has always helped young researchers to grow and develop, and we will forever miss and remember you.

Bing Tan (University of Electronic Science and Technology of China) (2021/01/18)

I am very sorry to hear that Professor Wataru Takahashi passed away. Professor Takahashi has always been highly esteemed as a senior and a researcher. I once finished several articles under his guidance. I was truly impressed by his passion and love of math. As he always said, "I have many ideas." Thank you for your guidance and advice, Professor Takahashi.

Chih-Sheng Chuang (2021/01/18)

I would like to express my sincere condolences on the passing of Professor Wataru Takahashi. I clearly remember that he gave us the exercise of functional analysis in Tokyo Institute of Technology about fifty years ago. I am proud to have only one paper as a coauthor with him. Please send my deep condolences to his family.

Kenjiro Yanagi (2021/01/22)

Prof. Wataru Takahashi was one of my great mentor. He had been willing to help and give me valuable suggestions. He was a good example for me and young mathematicians. I will always keep his teaching in my mind. Rest in Peace my SENSEI.

Warunun Inthakon (2021/02/02)

I am very sad to hear that Professor Takahashi passed away on 19 November 2020. He was an excellent mathematician, and an outstanding human being. My heartfelt condolences to his family.

Kok Lay Teo (2021/02/08)

Prof. Wataru Takahashi will live in our hearts for his great friendship, perfect organization of international conferences and important contributions to nonlinear analysis. We lost a dear friend. Japan lost a world-renowned mathematician.

Jie Sun (National University of Singapore and Curtin University, Australia) (2021/02/08)

Not only the great mathematician, he was the great teacher. He gave me and other student good opportunity.

Thank you very much, with best regards,

Attapol Kaewkhao (2021/02/09)


佐藤健治 (2021/02/10)

The moments spent with him during NACA-ICOTA 2019 will remain unforgettable to me. I learnt a lot from him. My condolences for his family.

Pushkar Jaisawal (2021/02/17)

I want to console you over the death of Professor Wataru Takahashi, this is indeed a great loss to all of us in the field of Mathematics. The Fixed Point Family and the Mathematics Family will surely miss him. Accept my heartfelt condolences Professor.

Abubakar Muhammad Bakoji (2021/02/17)

I am really very sad to know the sudden demise of Prof. Wataru Takahashi. The moments spent with him during NACA-ICOTA 2019 will remain unforgettable to me. I learnt a lot from him. My condolences for his family.

Vivek Laha (2021/02/17)

I would like to offer my condolences about Prof. Wataru Takahashi passed away on 19 November 2020. He was a very nice man and a great mathematician. We will keep him in our memories forever.

Phikul Sridarat (2021/02/17)

Memory of Wataru Takahashi

Hong-Kun Xu (2021/02/21)

I received the demise of Professor Wataru Takahashi with huge shock. Professor Takahashi was a respected mathematician not only in Japan or Asia, but around the world.

I met Professor Takahashi in the early stage of my carrier and have been closely following his excellent contributions in the field of nonlinear analysis, in particular, and many field of mathematics, in general. He will also be remembered by his contributions to fixed point theory conferences as either an organizer or a plenary speaker where many students get inspirations.

On behalf of my students and the entire KMUTT-Fixed Point Theory and Applications Research Group family, Bangkok, Thailand, I sincerely send my heartfelt condolences to the family and close associate of Professor Wataru Takahashi. He will surely be missed and am very sure his contributions to knowledge will definitely immortalize him.

Poom Kumam, Ph.D. (Professor at Department of Mathematics, KMUTT Head, KMUTT-Fixed Point Theory and Applications Research Group, Center of Excellence in Theoretical and Computational Science Center (TaCS-CoE).) (2021/02/26)

I first met Professor Wataru Takahashi when I was an undergraduate student in the department of information science, Tokyo Institute of Technology. Then in the department, there were two teachers named "Takahashi". So we called him friendly "Wataru Sensei" in our talk. Actually he was kind to us and his lectures were fun for us. We gathered in his laboratory, played and enjoyed mathematics and shared a lot of time together.

Since I heard the sad news, I have read some essays written by him. I called to mind his words; 数学は大人になるための学問である. In English, "Mathematics is a discipline for being a man". (Original his words are in Japanese, so I don't know if they are translated correctly.) I hope that Wataru Sensei will continue to encourage us to be a man each in his own place and in our mind.

Masashi Toyoda (2021/03/04)

So sad to read this news. I'd like to offer my deepest sympathy to Professor Takahashi's family and friends at this sad time. He will be warmly remembered and never forgotten.

Shahram Saeidi (2021/03/10)

Prof. Wataru Takahashi was not just a great mathematician, he was my source of inspiration and motivation. Thank you for the warm welcome and excellent care when I was studied in 2006-2007 at Tokyo Institute of Technology, Japan. Though we cannot see him or meet him but he will always stay alive and smiling in my memories and hearts. May Prof. Wataru Takahashi soul rest in peace.

Tanakit Thianwan (2021/04/15)

I am sad to hear that Prof. W. Takahashi passed away. Wataru Sensei is respected. His passing is a great loss to the mathematical world。 I would like to express my sincere condolences to the families.

Jinping Zhang (2021/04/17)


成川康男 (2021/05/23)

I would like to express my sincere condolences on the passing of Professor Wataru Takahashi. I remember very clearly that he gave me many helpful suggestions in Nonlinear Functional Analysis in Kaohsiung, Taiwan. I am proud to have some papers as a coauthor with him. Please send my deep condolences to his family.

Eskandar Naraghirad (2021/06/30)

Dear Family and Friends of Professor Wataru Takahashi:

Today is the memorial day when Prof.Takahashi passed way in 2020. I had been sorry and grieved to hear that one year ago and I could not still believe it. He provided me several proposals and chances to collaborate me to organize international activities including NACA and NAO as well as RIMS workshops. He gave me several suggestions and advice with many mathematical sounds. There are his great contributions to the progress in Nonlinear Analysis and Convex Analysis as well as many other areas. Moreover, he cared me with warm messages concerning my health several times.

He did a great contribution for the mathematical community. We remember forever his personality and activity.

Tamaki Tanaka (2021/11/19)

I am deeply saddened to hear the passing of Pr. Takahashi Wataru. From 1987 to 1990, I was Pr. Takahashi's graduate student at the Tokyo Institute of Technology. His kindness and depth of knowledge in math inspired me a lot to continue my journey in academia. I owe him a great deal today. May his soul rest in peace and his family be comforted.

Kone Mamadou Tadiou (2022/01/07)