Math Links

Mathscinet  American Mathematical Society-(Mathematical Reviews of the Web)
arXiv  Cornell University Library-
(arXiv is an e-print service in the fields of physics, mathematics,
non-linear science, computer science, and quantitative biology).
UC Davis  front end for the mathematics arXiv, maintained at Cornell University.

AMS  American Mathematical Society-(Mathematics Research and Scholarship)
CMS  Canadian Mathematical Society
EMS  The European Mathematical Society-(European Mathematical Information Service)
DBW  Links to Combinatorial Conferences - Douglas West
PJC  British Combinatorial Committee-(British Combinatorial Conferences) - Peter Cameron

ANCO  Annals of Combinatorics
CCA  Combinatorica
CDM  Contributions to Discrete Mathematics

CPC Combinatorics, Probability and Computing
DM   Discrete Mathematics
DAM  Discrete Applied Mathematics

EJC  The Electronic Journal of Combinatorics
ELA  Electronic Journal of LINEAR ALGEBRA-(Published by ILAS - The International Linear Algebra Society)
EURJC   European Journal of Combinatorics
GC  Graphs and Combinatorics

JACO  Journal of Algebraic Combinatorics
JCTA   Journal of Combinatorial Theory, Series A
JCTB   Journal of Combinatorial Theory, Series B

JGT  Journal of Graph Theory
JOC  Journal of Combinatorics

LAA  Linear Algebra and its Applications

LAMA  Linear and Multilinear Algebra
RSA  Random Structures and Algorithms

SIDMA  SIAM Journal on Discrete Mathematics

U of Delaware Math Seminars  
U of Delaware CS Seminars


Here are some of my papers and preprints. If you have any comments or suggestions, please send me an email. More about my activities here


  Papers & Preprints

  1. The smallest eigenvalues of Hamming graphs, Johnson graphs and other distance-regular graphs with classical parameters, with Andries Brouwer, Ferdinand Ihringer and Matt McGinnis, submitted.
  2. Spectral and combinatorial properties of some algebraically defined graphs, with Felix Lazebnik and Shuying Sun, submitted.
  3. Distributed Calculation of Edge-Disjoint Spanning Trees for
    Robustifying Distributed Algorithms against Man-in-the-Middle Attacks
    , with
    Gabriele Oliva and Christoforos Hadjicostis, IEEE Transactions on Control of Network Systems (2017+)
  4. Cospectral mates to the union of some classes in the Johnson association scheme, with Willem Haemers, Travis Johnston and Matt McGinnis, Linear Algebra and its Applications, (2018).
  5. Addressing graph products and distance-regular graphs, with Randy Elzinga, Michelle Markiewitz, Kevin Vander Meulen and Trevor Vanderwoerd, Discrete Applied Math. (2017).
  6. The graphs with all but two eigenvalues 0 or -2, with Willem Haemers and Jason Vermette, Designs, Codes and Cryptography (2017).
  7. Max-cut and extendability of matchings in distance-regular graphs, with Jack Koolen and Weiqiang Li, European Journal of Combinatorics (2017).
  8. Connectivity, toughness, spanning trees of bounded degrees, and spectrum of regular graphs, with Xiaofeng Gu , Czechoslovak Mathematics Journal dedicated to Professor Miroslav Fiedler, (2016).
  9. Spectral bounds for the k-independence number of a graph, with Aida Abiad and Michael Tait, Linear Algebra and its Applications, (2016).
  10. Maximizing the order of a regular graph of given valency and second eigenvalue, with Jack Koolen, Hiroshi Nozaki and Jason Vermette, SIAM J. Discrete Math. (2016).
  11. Notes on simplicial rook graphs, with Andries Brouwer, Willem Haemers and Jason Vermette, Journal of Algebraic Combinatorics dedicated to Godsil65 Conference (2016).
  12. Mixing rates of random walks with little backtracking, with Peng Xu, (2015) CRM Proceedings Series, published by the American Mathematical Society as part of the Contemporary Mathematics Series dedicated to Ram Murty 60th birthday conference.
  13. A graph partition problem, with Peter Cameron, American Math Monthly (2015).
  14. The graphs with all but two eigenvalues equal to 1, with Willem Haemers, Jason Vermette and Wiseley Wong, Journal of Algebraic Combinatorics (2015).
  15. The spectrum and toughness of regular graphs, with Wiseley Wong, Discrete Applied Mathematics (2014) Special Issue for CRM Applications of Graph Spectra in Computer Science. 
  16. On the spectrum of Wenger graphs, with Felix Lazebnik and Weiqiang Li, J.Combin. Theory Ser. B (2014).
  17. The extendability of matchings in strongly regular graphs, with Weiqiang Li, The Electronic Journal of Combinatorics (2014).
  18. Disconnecting strongly regular graphs, with Jack Koolen and Weiqiang Li, European Journal of Combinatorics , (2014).
  19. Ramanujan and expander graphs, with Ram Murty, invited and refereed chapter in Handbook of Finite Fields, Editors (Gary Mullen and Daniel Panario), (2013).
  20. On the connectedness of the complement of a ball in distance-regular graphs, with Jack Koolen, Journal of Algebraic Combinatorics, (2013).
  21. Variations on a theme of Graham and Pollak, with Michael Tait, Discrete Mathematics, (2013).
  22. Edge-disjoint spanning trees and eigenvalues of regular graphs, with Wiseley Wong, Linear Algebra and its Applications, (2012).
  23. Skew-adjacency matrices of graphs, with Michael Cavers, Shaun Fallat, David Gregory, Willem Haemers, Steve Kirkland, Judi McDonald and Michael Tsatsomeros, Linear Algebra and its Applications, (2012).
  24. On a conjecture of Brouwer regarding the connectivity of strongly regular graphs, with Kijung Kim and Jack Koolen, J.Combin. Theory Series A, (2012). Microsoft Research Presentation.
  25. Covering complete hypergraphs with cuts of minimum total size, with Andre Kundgen, Graphs and Combinatorics, (2012).
  26. More counterexamples to the Alon-Saks-Seymour and the Rank-Coloring Conjectures, with Michael Tait, The Electronic Journal of Combinatorics, (2011).
  27. Covering complete r-graphs with spanning complete r-partite r-graphs, with Andre Kundgen, Craig Timmons and Vladislav V. Vysotsky, Combinatorics, Probability and Computing, (2011).
  28. Some applications of eigenvalues of graphs, Chapter in Structural Analysis of Complex Networks, Birkhauser, (2011).
  29. Edge-connectivity, eigenvalues and matchings of regular graphs, with Suil O, SIAM J. Discrete Math., (2010).
  30. A necesssary and sufficient eigenvector condition for a connected graph to be bipartite, Electronic J. Linear Algebra, (2010).
  31. A lower bound for the spectral radius of graphs with fixed diameter, with Edwin van Dam, Jack Koolen and Jae-Ho Lee, European Journal of Combinatorics,  (2010).
  32. Eigenvalues and edge-connectivity of regular graphs, Linear Algebra and its Applications, (2010).
  33. Asymptotic results on the spectral radius and the diameter of graphs, with Edwin van Dam, Jack Koolen and Jae-Ho Lee , Linear Algebra and its Applications, (2010).
  34. A first course in graph theory and combinatorics, with Ram Murty, Hindustan Book Agency, 186 pages book, (2009). Errata
  35. On decompositions of complete hypergraphs, with Andre Kundgen and Jacques Verstraete, J.Combin. Theory Series A, (2009).
  36. Matchings in regular graphs from eigenvalues, with David Gregory and Willem Haemers, J.Combin.Theory Series B, (2009).
  37. The minimum degree distance of graphs with given order and size, with Orest Bucicovschi, Discrete Applied Math., (2008).
  38. Expander graphs and gaps between primes, with Ram Murty, Forum Mathematicum, (2008).
  39. Zero forcing sets and the minimum rank of graphs, Linear Algebra and its Applications, with 18 co-authors, (2008).
  40. Spectral independence number and densest subgraph of a graph, with Reid Andersen, Journal of Universal Computer Science, (2007).
  41. The spectral radius and the maximum degree of irregular graphs, The Electronic Journal of Combinatorics, (2007).
  42. Principal eigenvectors of irregular graphs, with David Gregory, Electronic Journal of Linear Algebra, (2007).
  43. Extreme eigenvalues of nonregular graphs, with David Gregory and Vlado Nikiforov, J.Combin.Theory Series B, (2007).
  44. Large matchings from eigenvalues, with David Gregory, Linear Algebra and its Applications, (2007).
  45. Closed walks and eigenvalues of Abelian Cayley graphs, Comptes Rendus Mathematique, (2006).
  46. Eigenvalues of graphs and a simple proof of a theorem of Greenberg, Linear Algebra and its Applications, (2006).
  47. On the extreme eigenvalues of regular graphs, J.Combin.Theory Series B, (2006).
  48. Sums of powers of the degrees of a graph, Discrete Mathematics, (2006).
  49. Eigenvalues, Expanders and Gaps between Primes, Ph.D. Thesis (2006), +90pp.
  50. Perfect matchings, eigenvalues and expansion , Comptes Rendus Mathematiques,Vol.27 (2005).
  51. Bounds on the Turan density of PG(3,2), The Electronic Journal of Combinatorics, 11, (2004).
  52. Problem 11066, American Math. Monthly 111 (2004). Solution
  53. The NP-completness of some edge partitioning problems, M.Sc. Thesis, (2002).

Upcoming Conferences/Seminars

Recent Conferences/Seminars

Some Old Talks

Graduate Students 

1. Michael Tait
M.Sc. 2010-2011; Ph.D. student at UC at San Diego working with Jacques Verstraete

2. Wiseley Wong Ph.D. 2010-2013; Lecturer at  University of Maryland.

3. Jason Vermette Ph.D. 2011-2015, defended on April 23, 2015; Since Fall 2015, Jason is a Tenure-Track Assistant Professor at Missouri Baptist University

4. Weiqiang (Ricky) Li Ph.D. 2011-2015, defended on May 18, 2015; working at Google.

5. Peng Xu Ph.D. 2013-2017 (co-supervised with Mokshay Madiman) will start a Tenure-track job as Assistant Professor at Eastern Michigan University in Fall 2017.

6. Matt McGinnis Ph.D. 2014-201?

Undergraduate Research Students

  1. Cory Cutsail, Summer 2016          Poster
  2. Stephanie Clampitt, Summer 2016          Poster
  3. Nicole DiPasquale, Summer 2016          Poster
  4. Pasquale Zingo, Summer 2016          Poster
  5. Yi Zhang, Summer 2015          Poster
  6. Briana Lamet, Summer 2015  Poster
  7. Yi Zhang, Summer 2014         Poster
  8. Emma Kulek, Summer 2014   Poster
  9. Alexandra Sampugnaro, Summer 2013
  10. Michelle Markiewitz, Summer 2012  Poster
  11. Dajun Lin, Summer 2011     Poster
  12. Patrick Devlin, Summer 2010    Poster
  13. Michael Tait, Summer 2010


"There is no problem
in all mathematics
that cannot be solved
by direct counting."

Ernst Mach

address:  Sebastian (Sebi) Cioaba
University of Delaware,
Department of Mathematical Sciences
  Ewing Hall, Room 506

Office phone: (302) 831 1866
Newark  DE 19716-2553
cioaba at udel dot edu

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