Jack Koolen's Home page

    Professional Experiences:

• 2013.08~              : Professor, University of Science and Technology of China (USTC), Hefei, China.
• 2005.02~2013.08 : Associate Professor, Postech, Pohang, Korea.
• 2003.03~2005.01 : Visiting Assistant Professor, KAIST, Daejon, Korea.
• 2002.01~2003.02 : Visiting Assistant Professor, Postech, Pohang, Korea.
• 2001.08~2001.12 : Visiting Assistant Professor, University of Wisconsin, Madison, USA.
• 1999.11~2001.08 : Scientific Assistant at Bielefeld University.
• 1998.09~1999.09 : Scientific Assistant at Center for Mathematics and Computer Science, Amsterdam.
• 1995.04~1998.08 : Post doctoral fellow at Kyushu University, Bielefeld University Royal Institute of Technology, Sweden, Oxford University and Lisbon University.

    Major Fields:

• Algebraic Combinatorics.
• Spectral Graph Theory.
• Geometric Combinatorics.

    Selected Papers : 

2014

• Jang, Hye Jin; Koolen, Jack; Munemasa, Akihiro; Taniguchi, Tetsuji On fat Hoffman graphs with smallest eigenvalue at least $-3$. Ars Math. Contemp. 7 (2014), no. 1, 105-121.

2013

• Cioabă, Sebastian M.; Koolen, Jack H. On the connectedness of the complement of a ball in distance-regular graphs. J. Algebraic Combin. 38 (2013), no. 1, 191-195.

• Koolen, Jack H.; Park, Jongyook A note on distance-regular graphs with a small number of vertices compared to the valency. European J. Combin. 34 (2013), no. 6, 935-940.

• Koolen, Jack H.; Kim, Joohyung; Park, Jongyook Distance-regular graphs with a relatively small eigenvalue multiplicity. Electron. J. Combin. 20 (2013), no. 1, Paper 1, 12 pp.

• Koolen, Jack H.; Markowsky, Greg; Park, Jongyook On electric resistances for distance-regular graphs. European J. Combin. 34 (2013), no. 4, 770-786.

2012

• Grünewald, Stefan; Koolen, Jack H.; Moulton, Vincent; Wu, Taoyang The size of 3-compatible, weakly compatible split systems. J. Appl. Math. Comput. 40 (2012), no. 1-2, 249-259.

• Koolen, Jack H.; Park, Jongyook A relationship between the diameter and the intersection number $c_2$ for a distance-regular graph. Des. Codes Cryptogr. 65 (2012), no. 1-2, 55-63.

• Koolen, Jack H.; Lesser, Alice; Moulton, Vincent; Wu, Taoyang Injective optimal realizations of finite metric spaces. Discrete Math. 312 (2012), no. 10, 1602-1610.

• Cioabă, Sebastian M.; Kim, Kijung; Koolen, Jack H. On a conjecture of Brouwer involving the connectivity of strongly regular graphs. J. Combin. Theory Ser. A 119 (2012), no. 4, 904-922.

• Koolen, Jack H.; Park, Jongyook Distance-regular graphs with $a_1$ or $c_2$ at least half the valency. J. Combin. Theory Ser. A 119 (2012), no. 3, 546-555.

• Dress, Andreas; Huber, Katharina T.; Koolen, Jacobus; Moulton, Vincent; Spillner, Andreas Basic phylogenetic combinatorics. Cambridge University Press, Cambridge, 2012. xii+264 pp. ISBN: 978-0-521-76832-0.

2011

• Dress, A. W. M.; Huber, K. T.; Koolen, J.; Moulton, V. Blocks and cut vertices of the Buneman graph. SIAM J. Discrete Math. 25 (2011), no. 4, 1902-1919.

• Chung, Taeyoung; Koolen, Jack; Sano, Yoshio; Taniguchi, Tetsuji The non-bipartite integral graphs with spectral radius three. Linear Algebra Appl. 435 (2011), no. 10, 2544-2559.

• Koolen, Jack H.; Yu, Hyonju The distance-regular graphs such that all of its second largest local eigenvalues are at most one. Linear Algebra Appl. 435 (2011), no. 10, 2507-2519.

• Koolen, Jack H.; Park, Jongyook; Yu, Hyonju An inequality involving the second largest and smallest eigenvalue of a distance-regular graph. Linear Algebra Appl. 434 (2011), no. 12, 2404-2412.

• Jurišić, Aleksandar; Koolen, Jack Classification of the family ${\rm AT4}(qs,q,q)$ of antipodal tight graphs. J. Combin. Theory Ser. A 118 (2011), no. 3, 842-852.

2010

• Koolen, Jacobus H.; Lee, Woo Sun; Martin, William J. Characterizing completely regular codes from an algebraic viewpoint. Combinatorics and graphs, 223-242, Contemp. Math., 531, Amer. Math. Soc., Providence, RI, 2010.

• Dress, Andreas; Huber, Katharina T.; Koolen, Jacobus; Moulton, Vincent; Spillner, Andreas An algorithm for computing cutpoints in finite metric spaces. J. Classification 27 (2010), no. 2, 158-172.

• Akbari, Saieed; Ghorbani, Ebrahim; Koolen, Jack H.; Oboudi, Mohammad Reza A relation between the Laplacian and signless Laplacian eigenvalues of a graph. J. Algebraic Combin. 32 (2010), no. 3, 459-464.

• Koolen, Jack H.; Park, Jongyook Shilla distance-regular graphs. European J. Combin. 31 (2010), no. 8, 2064-2073.

• Koolen, J. H.; Bang, S. On distance-regular graphs with smallest eigenvalue at least $-m$. J. Combin. Theory Ser. B 100 (2010), no. 6, 573-584.

• Akbari, Saieed; Ghorbani, Ebrahim; Koolen, Jacobus H.; Oboudi, Mohammad Reza On sum of powers of the Laplacian and signless Laplacian eigenvalues of graphs. Electron. J. Combin. 17 (2010), no. 1, Research Paper 115, 8 pp.

• Cioabă, Sebastian M.; van Dam, Edwin R.; Koolen, Jack H.; Lee, Jae-Ho A lower bound for the spectral radius of graphs with fixed diameter. European J. Combin. 31 (2010), no. 6, 1560-1566.

• Markowsky, Greg; Koolen, Jacobus A conjecture of Biggs concerning the resistance of a distance-regular graph. Electron. J. Combin. 17 (2010), no. 1, Research Paper 78, 15 pp.

• Bang, S.; Hiraki, A.; Koolen, J. H. Delsarte set graphs with small $c_2$. Graphs Combin. 26 (2010), no. 2, 147-162.

• Cioabă, Sebastian M.; van Dam, Edwin R.; Koolen, Jack H.; Lee, Jae-Ho Asymptotic results on the spectral radius and the diameter of graphs. Linear Algebra Appl. 432 (2010), no. 2-3, 722-737.

    Workshop and Conference:

• KNU-PNU-PMI Algebraic Combinatorics Workshop
• Korea-Japan Workshop on Algebra and Combinatorics
• Discovering Patterns in Biology
• PMI Phylogenetic Combinatorics Seminar
• ALGEBRAIC AND GEOMETRIC COMBINATORICS CONFERENCE 2010