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BEGIN:VEVENT
SUMMARY:Shariefuddin Pirzada (University of Kashmir\, India)
DTSTART:20210714T070000Z
DTEND:20210714T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/1
DESCRIPTION:Title: The Laplacian Eigenvalues of Graphs\nby Shariefuddin Pirzada
(University of Kashmir\, India) as part of Combinatorics Today Series - I
TB\n\nAbstract: TBA\n\nShariefuddin PIRZADA\nProfessor\nDepartment of Math
ematics University of Kashmir Srinagar\, Kashmir\, India.\nDean School of
Physical and Mathematical Sciences\, November 8\, 2017-till date\nHead Dep
artment of Mathematics\, April 2021-till date\nPreviously\, He taught at K
ing Fahd University of Petroleum and Minerals (2008-2011).\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Oriol Serra (Universitat Politecnica de Catalunya\, Barcelona\, S
pain)
DTSTART:20210810T080000Z
DTEND:20210810T093000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/2
DESCRIPTION:Title: Combinatorial Nullstellensatz\nby Oriol Serra (Universitat P
olitecnica de Catalunya\, Barcelona\, Spain) as part of Combinatorics Tod
ay Series - ITB\n\n\nAbstract\nThe Combinatorial Nullstellensatz is an alg
ebraic tool aimed to treat combinatorial problems. After its systematic se
t up by Alon at the end of last century the tool has been applied to a div
ersity of problems and some extensions have been explored. In the talk\, s
ome chosen examples are given which illustrate particular aspects of the a
pplication of the method and some of its recent extensions. In particular
a recent application on counting field colorings in planar graphs will be
discussed.\n\nProfessor Oriol SERRA \nDepartment of Mathematics Universita
t Polytecnica de Catalunya\, Barcelona Spain. \nCo-Chair Research Group of
Geometric\, Algebraic and Probabilistic Combinatorics.\n\nVisiting positi
ons at University of California Santa Cruz (1994-95)\, \nENS Telecommunica
tions Paris (2000)\, \nRenyi Institute Budapest (2001)\, \nCharles Univers
ity Prague (2005)\, \nInstitute de Mathmatiques de Bordeaux (2012).\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ian Wanless (Monash University\, Australia)
DTSTART:20210824T070000Z
DTEND:20210824T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/3
DESCRIPTION:Title: Diagonally Cyclic Latin Squares\nby Ian Wanless (Monash Univ
ersity\, Australia) as part of Combinatorics Today Series - ITB\n\n\nAbstr
act\nA Latin square is a square matrix in which each row and column is a\n
permutation of the same set of symbols. Examples include Cayley tables\nof
finite groups and completed sudoku puzzles. A Latin square is\ndiagonally
cyclic if the symbols occur in cyclic order along each\nbroken diagonal p
arallel to the main diagonal. An example of order 7\, with \none of its cy
clic diagonals highlighted\, is\n\n\\[\n \\left[\n \\begin{array}{ccccccc}
\n 0& 2&\\fbox 5& 1& 6& 4& 3\\\\\n 4& 1& 3&\\fbox 6& 2& 0& 5\\\\\n 6& 5
& 2& 4&\\fbox 0& 3& 1\\\\\n 2& 0& 6& 3& 5&\\fbox 1& 4\\\\\n 5& 3& 1& 0&
4& 6&\\fbox 2\\\\\n \\fbox 3& 6& 4& 2& 1& 5& 0\\\\\n 1& \\fbox 4& 0& 5&
3& 2& 6\\\\\n \\end{array}\n \\right]\n \\]\n\nAn orthomorphism of an abel
ian group $G$ is a permutation\n$\\theta:G\\mapsto G$ such that the map $x
\\mapsto\\theta(x)-x$ is also a\npermutation of $G$. It is not hard to fin
d a bijection between\ndiagonally cyclic Latin squares and orthomorphisms
of cyclic groups.\nI will review the history and applications of diagonall
y cyclic Latin\nsquares and orthomorphisms\, including reporting new resul
ts of two\ncurrent projects of mine\, one of which is joint with Ale\\v s
Dr\\'apal\n(Charles University\, Prague) and the other is joint work with
my student\nJack Allsop.\n\nProfessor Ian WANLESS\nSchool of Mathematics\,
Monash University\, Australia\n\nAcademic awards and achievements:\n2017
B.H. Neumann award from the Australian Mathematics Trust\nFor leadership\,
support and encouragement for mathematics and the\nteaching of mathematic
s at all levels\;\n2009 Medal of the Australian Mathematical Society\nAwar
d for excellence in a researcher under 40 years of age\;\n2008 Hall Medal
from the Institute of Combinatorics and its Applications.\nWorldwide award
for excellence in a researcher under 40 years of age\;\n2008 Victorian Yo
ung Tall Poppy Award.\nAwarded by the Australian Institute of Policy & Sci
ence for research excellence and community engagement\;\n2008 Monash Unive
rsity Faculty of Science award for best early career researcher\;\n2002 Ki
rkman Medal from the Institute of Combinatorics and its Applications\,\nWo
rldwide award for excellence in an early career researcher\;\nJ.G. Crawfor
d Prize\, 1998 (Best science PhD thesis at ANU in previous year)\;\nB.H. N
eumann Prize\, 40th annual AustMS meeting\, 1996 (best student talk).\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akira Saito (Nihon University\, Japan)
DTSTART:20210910T070000Z
DTEND:20210910T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/4
DESCRIPTION:Title: Implications in rainbow forbidden subgraphs\nby Akira Saito
(Nihon University\, Japan) as part of Combinatorics Today Series - ITB\n\n
\nAbstract\nLet $H$ and $H'$ be connected graphs.\nAn edge-colored graph $
G$ is rainbow if each edge receives a different color.\nAlso\,\n$G$ is rai
nbow $H$-free if $G$ does not contain a rainbow subgraph\nwhich is isomorp
hic to $H$.\nIf every rainbow $H'$-free complete graph edge-colored in suf
ficiently many colors\nis rainbow $H$-free\,\nwe write $H'\\le H$.\nMoreov
er\,\nif $H'$ is a subgraph of $H$\,\nwe write $H'\\subseteq H$\,\nand if
$H'\\subseteq H$ and $H\\ne H'$\,\nwe write $H'\\subsetneq H$. \n\nIt is e
asy to see that $H'\\subseteq H$ implies $H'\\le H$.\nOn the other hand\,\
nif $H\\subsetneq H'$\,\nthen we naturally do not expect $H'\\le H$.\nHowe
ver\,\nin $2015$\,\nBass\,\nMagnant\,\nOzeki and Pyron reported $K^+_{1\,3
}\\le K_{1\,3}$\,\nwhere $K_{1\,3}^+$ is the graph\nobtained from $K_{1\,3
}$\nby subdividing one edge with a single vertex.\nSince $K_{1\,3}\\subset
eq K^+_{1\,3}$\,\ntheir result says that even if $H\\subsetneq H'$\,\n$H'\
\le H$ possibly occurs.\n\nIn the former half of the talk\,\nwe further di
scuss this possibility.\nWe determine all the pairs $(H\, H')$ with $H\\su
bsetneq H'$ and\n$H'\\le H$.\nThis part is a joint work with\nQing Cu\, Qi
nghai Liu and Colton Magnant.\n\\par\nIn the latter half\,\nwe give an ove
rview of the ongoing project to study the pairs $(H\, H')$ with $H'\\le H$
\nwhen neither $H$ nor $H'$ is a subgraph of the other.\nWe will encounter
many strange pairs\,\nwhich suggest that as a binary relation\,\n$\\le$ i
s much more complicated\nthan the subgraph relation $\\subseteq$.\n\nProfe
ssor Akira Saito\, Nihon University\, Japan.\n\nAkira Saito received Bache
lor's\, Master's and Doctor's degrees in Science from\nThe University of T
okyo in 1981\, 1983 and 1986\, respectively. In 1986\, he started his care
er as an assistant professor at Tohoku University. Then he moved to Nihon
University as a lecturer in 1986. Currently\, he is a professor at Departm
ent of Information Science\, Nihon University.\nHe was a visiting lecturer
at Otago University\, New Zealand\, in 1988--1989\nand a visiting profess
or at The University of Memphis\, U.S.A.\, in 1996--1997.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cheryl Praeger (The University of Western Australia\, Australia)
DTSTART:20210924T063000Z
DTEND:20210924T080000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/5
DESCRIPTION:Title: Codes and designs in Johnson graphs\nby Cheryl Praeger (The
University of Western Australia\, Australia) as part of Combinatorics Toda
y Series - ITB\n\n\nAbstract\nThe Johnson graph $J(v\, k)$ has\, as vertic
es\, all $k$-subsets of a $v$-set $\\mathcal{V}$\, with two $k$-subsets ad
jacent if and only if they share $k-1$ common elements of $\\mathcal{V}$.
Subsets of vertices of $J(v\, k)$ can be interpreted as the block-set of
an incidence structure\, or as the set of codewords of a code\, and automo
rphisms of $J(v\, k)$ leaving the subset invariant are then automorphisms
of the corresponding incidence structure or code. \n \nThis approach leads
to interesting new designs and codes. For example\, numerous actions of
the Mathieu sporadic simple groups give rise to examples of Delandtsheer d
esigns (which are both flag-transitive and anti-flag transitive)\, and cod
es with large minimum distance (and hence strong error-correcting properti
es).\n \nIn my talk I will explore links between designs and codes in John
son graphs which have a high degree of symmetry\, and I will mention sever
al open questions.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chie NARA (Meiji University\, Japan)
DTSTART:20211008T070000Z
DTEND:20211008T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/6
DESCRIPTION:Title: Recent Results in Continuous Flattening Problems of Polyhedra\nby Chie NARA (Meiji University\, Japan) as part of Combinatorics Today
Series - ITB\n\n\nAbstract\nA. Cauchy used Graph Theory (GT) effectively i
n the proof of his famous theorem “Cauchy’s Rigidity Theorem” in 181
3\, which says that the surface of a convex polyhedron cannot be continuou
sly transformed to any non-congruent polyhedron if all the faces are rigid
. We sometimes encounter the difficulty of describing precise proofs of fa
cts obtained intuitively and find some ways by applying GT as Cauchy did.
A continuous flattening problem of polyhedra was asked by E. Demaine et al
. in 2001: Can we flatten a polyhedral surface with non-rigid faces withou
t tearing and stretching? I have been working on this problem more than a
decade. In this talk\, I will introduce several results including recent r
elated works and show where GT is implicitly used. As an application of th
ose results\, I will introduce examples of convex polyhedra whose faces ar
e rigid except infinitesimally small parts\, which can be continuously fla
ttened.\n\nChie Nara received her BA\, MA\, and Ph.D. degrees in Mathemati
cs from the Ochanomizu University in Tokyo. While she worked at Tokyo City
University as a lecturer\, she was offered a scholarship and visited Alle
n Shield at the University of Michigan as a visiting scholar one year for
the research of the functional analysis. In 2001\, she took a position at
the Tokai University to work in the discrete geometry as well as the educa
tional development\, became a professor\, and retired in 2014. After then\
, she has been working at the Meiji University as a visiting researcher (p
rofessor for two years)\, and her research field has been extended to the
Origami engineering\, added to the discrete geometry. She translated a fam
ous book “Introduction to Graph Theory with Applications” by Bondy and
Murty into Japanese in 1991 and wrote a book “Origami Science” publis
hed in 2019.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Peter Cameron (University of St Andrews\, United Kingdom)
DTSTART:20211022T080000Z
DTEND:20211022T093000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/7
DESCRIPTION:Title: Graphs defined on groups\nby Peter Cameron (University of St
Andrews\, United Kingdom) as part of Combinatorics Today Series - ITB\n\n
\nAbstract\nThere has been a lot of recent interest on graphs whose vertex
set is a group G and whose edges reflect the structure of G: examples inc
lude the commuting graph\, the generating graph\, and the power graph. It
is possible to arrange these graphs in a hierarchy\, and compare their pro
perties\, as well as look at properties of the differences between success
ive graphs in the hierarchy.\n\nI was born in Toowoomba\, Australia\, and
studied at the University of Queensland and Oxford University\, taking my
DPhil at Oxford under the supervision of Peter Neumann. After a postdoc\,
I held teaching positions in Oxford and then Queen Mary University of Lond
on\, where I retired in 2012. Since then I have been a half-time professor
at the University of St Andrews (Scotland's oldest university). I work mo
stly in group theory and combinatorics: my real interest is groups acting
on structures of various kinds\, but I also have worked in model theory an
d (briefly) in mathematical psychology. I have over 300 publications and h
ave supervised around 40 PhD students. Awards include the Senior Whitehead
Prize from the London Mathematical Society and the Euler medal from the I
nstitute for Combinatorics and its Applications.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Martin Grohe (RWTH AACHEN University\, Germany)
DTSTART:20211119T070000Z
DTEND:20211119T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/8
DESCRIPTION:Title: The Logic of Graph Neural Networks\nby Martin Grohe (RWTH AA
CHEN University\, Germany) as part of Combinatorics Today Series - ITB\n\n
\nAbstract\nGraph neural networks (GNNs) are a deep learning architecture
for graph structured data that has developed into a method of choice for m
any graph learning problems in recent years. It is therefore important tha
t we understand their power. One aspect of this is the expressiveness: whi
ch functions on graphs can be expressed by a GNN model? Surprisingly\, thi
s question has a precise answer in terms of logic and a combinatorial algo
rithm known as the Weisfeiler Leman algorithm.\n\nMy talk will be a survey
of recent results linking the expressiveness of\nGNNs to logical expressi
vity.\n\nMartin Grohe is a Professor for Theoretical Computer Science at t
he RWTH Aachen. He received his PhD in Mathematics at Freiburg University
in 1994 and then spent a year as a visiting scholar at Stanford and the Un
iversity of California at Santa Cruz. Before joining the Department of Com
puter Science of RWTH Aachen in 2012\, he held positions at the University
of Illinois at Chicago\, the University of Edinburgh\, and the Humboldt U
niversity at Berlin.\n\nHis research interest are in theoretical computer
science interpreted broadly\, including logic\, algorithms and complexity\
, graph theory\, theoretical aspects of machine learning\, and database th
eory.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tom Kelly (University of Birmingham\, United Kingdom)
DTSTART:20211126T080000Z
DTEND:20211126T093000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/9
DESCRIPTION:Title: Coloring hypergraphs of small codegree\, and a proof of the Erd
ős–Faber–Lovász conjecture\nby Tom Kelly (University of Birmingh
am\, United Kingdom) as part of Combinatorics Today Series - ITB\n\n\nAbs
tract\nThe theory of edge-coloring hypergraphs has a rich history with imp
ortant connections and application to other areas of combinatorics e.g. de
sign theory and combinatorial geometry. A long-standing problem in the fi
eld is the Erdős–Faber–Lovász conjecture (posed in 1972)\, which sta
tes that the chromatic index of any linear hypergraph on n vertices is at
most n. In joint work with Dong Yeap Kang\, Daniela Kühn\, Abhishek Meth
uku\, and Deryk Osthus\, we proved this conjecture for every sufficiently
large n. Recently\, we also solved a related problem of Erdős from 1977
on the chromatic index of hypergraphs of small codegree. In this talk\, I
will survey the history behind these results and discuss some aspects of
the proofs.\n\nTom Kelly received his Bachelor's degree from Princeton Uni
versity in 2015\, where he was awarded the Middleton Miller '29 prize for
best independent work in mathematics. He then obtained his PhD in Combina
torics & Optimization from the University of Waterloo in 2019\, where he w
as awarded the first-place Mathematics Doctoral Prize and was a University
Finalist for the Governor General's Gold Medal. He is currently a Resear
ch Fellow at the University of Birmingham.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Catherine Greenhill (University of New South Wales\, Australia)
DTSTART:20211210T070000Z
DTEND:20211210T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/10
DESCRIPTION:Title: Results about random hypergraphs\, proved using asymptotic enum
eration formulae\nby Catherine Greenhill (University of New South Wale
s\, Australia) as part of Combinatorics Today Series - ITB\n\n\nAbstract\n
Hypergraphs are generalisations of graphs\, where each edge is a subset of
the vertex set. In a uniform hypergraph\, every edge has the same size: f
or example\, a graph is a 2-uniform hypergraph. Asymptotic enumeration inv
olves finding an approximate formula for a combinatorial set\, such as the
number of hypergraphs with given properties. The formula has a relative e
rror that gets smaller as the number of vertices grows. As well as being
interesting in their own right\, these formulae can be very useful tools w
hich can help us prove results about random hypergraphs\, or analyse rando
mised algorithms for hypergraphs. I will illustrate this by describing how
my co-authors and I have used asymptotic enumeration formulae to prove th
ree very different results involving hypergraphs:\n(1) One result is the a
nalysis of an algorithm for randomly generating uniform hypergraphs with a
given degree sequence\;\n(2) Another result describes the degree distribu
tion of a random uniform hypergraph with a given number of edges\;\n(3) An
other result establishes a threshold for the existence of a 2-factor (span
ning 2-regular subhypergraph) in random regular uniform hypergraphs.\n\nCa
therine Green hill is a professor at the School of Mathematics and Statist
ics\, University of New South Wales\, Australia. She was awarded the 2015
Christopher Heyde Medal in Pure Mathematics by the Australian Academy of S
cience and the 2010 Hall Medal by the Institute of Combinatorics and its A
pplications.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Camino Balbuena (Universitat Politecnica de Catalunya\, Spain)
DTSTART:20220128T070000Z
DTEND:20220128T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/11
DESCRIPTION:Title: Moore Cages of Girth 8\nby Camino Balbuena (Universitat Pol
itecnica de Catalunya\, Spain) as part of Combinatorics Today Series - ITB
\n\n\nAbstract\nIn this talk we explain some problems related with graphs
called cages of girth\n8. These graphs are regular\, have girth 8\, and ha
ve the least possible number of vertices.\nThe lower bound on this value i
s easy to obtain\, and the cages with order equal to the lower\nbound are
called Moore cages of girth 8. We will give an algebraic description of Mo
ore\n$(q+1\,8)$-cages\, where $q \\geq 2$ denotes a prime power. Starting
of this description we will\nexplain how to obtain graphs of girth 8 and d
egrees $q$ or $q-1$ having the minimum number\nof vertices known until now
. Also the algebraic description of Moore $(q+1\,8)$-cages allows\nus to o
btain $k$-regular graphs of girth $7$ having the minimum number of vertice
s known until\nnow.\n\nProf Camino Balbuena:\nIn 1989 she joined the Unive
rsitat Politecnica de Catalunya and in 1995 she received the Phd degree fr
om the same university. Since then she has been working with the Research
Group on Combinatorics\, Graph Theory and Applications (COMBGRAF). Her res
earch is focused on Fault-Tolerance of networks and the construction of ex
tremal graphs with prescribed parameters. Most of her research is concerne
d to the study of conditional connectivity and particularly on the restric
ted edge connectivity of graphs and digraphs.\n\nOne remarkable contributi
on that she has made is the best known breakthrough in the solution of the
conjecture claiming that cages are maximally connected by proving for odd
girth that the connectivity is at least the degree divided by two. The st
udy of cages produced the need to obtain these objects more easily. She ha
s given a direct way for obtaining the adjacency matrix of any projective
plane of order a prime power\, which is equivalent to obtain cages of girt
h 6. Moreover\, she and her collaborators have given a simple formula for
obtaining generalized quadrangles or equivalently cages of girth 8. This k
nowledge has allowed to solve other related problems as the following:\n
• To construct the smallest known graphs of girth 5.\n• To prove a con
jecture about the construction of regular graphs with a given girth-pair h
aving the small number of vertices.\n• To find a family of graphs free o
f short cycles having m ximum number of edges.\n• To characterize bipa
rtite graphs of girth 6 having a (1\,≤𝑙𝑙)−Code and a good contri
bution in the study of graphs of girth 5 having an identifying code.\nIt d
eserves also to highlight that she and her collaborators have done a very
good advance in the conjecture claiming that any tree is graceful by provi
ng that an infinite family of trees is graceful.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nobuaki Obata (Tohoku University\, Japan)
DTSTART:20220218T070000Z
DTEND:20220218T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/12
DESCRIPTION:Title: Quadratic Embedding Constants of Graphs and Related Topics\
nby Nobuaki Obata (Tohoku University\, Japan) as part of Combinatorics Tod
ay Series - ITB\n\n\nAbstract\nThe quadratic embedding (QE) constant of a
finite \nconnected graph $G$\, denoted by $\\mathrm{QEC}(G)$\,\nis by defi
nition the maximum of the quadratic function \nassociated to the distance
matrix on a certain sphere \nof codimension two. The QE constant was intro
duced \naround 2018 by the speaker and has been expected to\nbe an interes
ting invariant of finite connected graphs.\nIn this lecture I will survey
basic results on the QE constant\,\ndiscuss some related topics and propos
e some questions.\n\nProf. Nobuaki Obata from Tohoku University Japan.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xueliang Li (Nankai University\, China)
DTSTART:20220408T070000Z
DTEND:20220408T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/13
DESCRIPTION:Title: Extremal Problems for Graphical Function-Indices and f-Weighted
Adjacency Matrices\nby Xueliang Li (Nankai University\, China) as par
t of Combinatorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hao Huang (NUS\, Singapore)
DTSTART:20220423T070000Z
DTEND:20220423T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/14
DESCRIPTION:Title: Interlacing Methods in Extremal Combinatorics\nby Hao Huang
(NUS\, Singapore) as part of Combinatorics Today Series - ITB\n\nAbstract
: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eiichi Bannai (Kyushu University\, Japan)
DTSTART:20220625T070000Z
DTEND:20220625T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/15
DESCRIPTION:Title: Explicit Construction of Exact Unitary Designs\nby Eiichi B
annai (Kyushu University\, Japan) as part of Combinatorics Today Series -
ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Brendan McKay (ANU\, Australia)
DTSTART:20220728T070000Z
DTEND:20220728T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/16
DESCRIPTION:Title: Ramsey Theory and Ramsey Numbers\nby Brendan McKay (ANU\, A
ustralia) as part of Combinatorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stanislaw Radziszowski (Rochester Isntitute of Technology\, USA)
DTSTART:20220825T120000Z
DTEND:20220825T133000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/17
DESCRIPTION:Title: More on Computational Approach in Ramsey Theory\nby Stanisl
aw Radziszowski (Rochester Isntitute of Technology\, USA) as part of Combi
natorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Linda Lesniak (Western Michigan University\, USA)
DTSTART:20220909T120000Z
DTEND:20220909T133000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/18
DESCRIPTION:Title: On the Necessity of Chvatal's Hamiltonian Degree Condition and
Forcibly P Degree Conditions\nby Linda Lesniak (Western Michigan Unive
rsity\, USA) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nIn
1972 Chvatal gave a well-known sufficient condition for a graphical seque
nce to be forcibly hamiltonian\, and showed that in some sense his conditi
on is best possible. Even though\, for each $n \\geq 3$\, we have construc
ted exponentially many forcibly hamiltonian $n$-sequences that do not sati
sfy Chvatal’s condition\, in this talk we will discuss why we conjecture
that the proportion of forcibly hamiltonian $n$-sequences that satisfy Ch
vatal’s condition approaches 1 exponentially fast. Informally\, with pro
bability approaching 1 as $n \\rightarrow 1$\; we conjecture that a graphi
cal $n$-sequence $\\pi$ is forcibly hamiltonian if and only if $\\pi$ sati
sfies Chvatal’s condition. In contrast\, we can essentially prove that f
or every $k \\geq 1$ the sufficient condition of Bondy and Boesch for forc
ible $k$-connectedness is not necessary in the same way. This suggests a m
ore general question for other monotone graphical properties $P$ that we w
ill discuss here.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akihiro Munemasa (Tohoku University\, Japan)
DTSTART:20220929T070000Z
DTEND:20220929T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/19
DESCRIPTION:Title: Sphere Packings\, Root Systems and Signed Graphs\nby Akihir
o Munemasa (Tohoku University\, Japan) as part of Combinatorics Today Seri
es - ITB\n\n\nAbstract\nIn 1981 Bannai and Sloane proved the uniqueness of
optimal configurations on the spheres in the Euclidean spaces of dimensio
n 8 and 24. For the dimension 8\, the set of 240 vectors of the root syste
m of type $E_8$ was shown to be the unique largest subset of the sphere in
which two vectors are at least 60 degrees apart. A slice of the root syst
em of type $E_8$ contains a set of 28 equiangular lines in the 7-dimension
al hyperplane. In 2021\, based on joint work with Cao\, Koolen and Yoshino
\, we showed that this set is characterized as the unique strongly maximal
set of equiangular lines in the sense that no more lines can be added eve
n if the dimension is allowed to increase. In this talk\, we propose a fra
mework to capture in a similar manner the slice of the 24-dimensional conf
iguration\, that is\, the set of 2300 lines determined by the shorter Leec
h lattice.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicholas Wormald (Monash University\, Australia)
DTSTART:20221013T070000Z
DTEND:20221013T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/20
DESCRIPTION:Title: Uniform generation of combinatorial objects\nby Nicholas Wo
rmald (Monash University\, Australia) as part of Combinatorics Today Serie
s - ITB\n\n\nAbstract\nIt can be useful to sample from a class of objects
uniformly at random\, for instance in order to test algorithms. This can
be easy if the objects can be counted in appropriate ways. Even approximat
e counts can be sometimes be used for exactly uniform sampling\, for insta
nce via rejection sampling. We discuss a family of algorithms that are use
ful for generating random graphs with given degrees\, and related structur
es such as Latin rectangles and statistical contingency tables. These algo
rithms achieve a precisely uniform distribution and can be implemented so
as to run in essentially optimal time provided that the objects being gene
rated are not very "dense".\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Edy Tri Baskoro (Institut Teknologi Bandung\, Indonesia)
DTSTART:20221029T070000Z
DTEND:20221029T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/21
DESCRIPTION:Title: On the Existence of Almost Moore Digraphs\nby Edy Tri Basko
ro (Institut Teknologi Bandung\, Indonesia) as part of Combinatorics Today
Series - ITB\n\n\nAbstract\nFor any integers $d \\geq 2$ and $k \\geq 1$\
, an almost Moore digraph is defined as a diregular digraph of degree $d$\
, diameter $k$ and order $d+d^2+ \\cdots + d^k$. The question of its exist
ence has attracted a lot of attention. For some small values of $d$ and $k
$ we have known the answer\, but for other cases the question remains open
. The structural study on these digraphs (if they exist) was initiated by
the work of Mirka Miller by introducing a repeat function. In this talk\,
we will discuss the beauty of repeat function used to explore the possibil
ity of the existence of almost Moore digraphs.\n\nEdy Tri Baskoro was born
in Jombang\, Indonesia\, received his a B.Sc degree in mathematics from I
nstitut Teknologi Bandung (ITB) Indonesia in 1987\, his Master degree from
University of New England Australia in 1992\, and his PhD degree from the
University of Newcastle\, Australia in 1996. Since then he has held a sen
ior academic position at ITB. Since July 2006\, he has been honoured a pro
fessor in mathematics of ITB. He served as the Dean of Faculty of Mathema
tics and Natural Sciences\, Institut Teknologi Bandung 2015-2019. He has b
een acknowledged as an adjunct professor at the University of Newcastle Au
stralia 2006-2015 and the Abdus Salam School of Mathematical Sciences\, GC
University\, Lahore Pakistan 2006-2015. Currently\, he serves as a chair
of the Professor Forum of ITB. \n\nHis main research interests are graph t
heory and combinatorics. He is a pioneer in the development of graph theor
y and combinatorics community in Indonesia. For his leadership\, he was el
ected as the President of Indonesian Combinatorial Mathematics Society (20
06-2013). For his contributions to these fields he has been awarded Habibi
e Award in Basic Science Research (2009)\, Australian Alumni Award for Exc
ellence in Education (2009)\, and the Extraordinary Intellectual Quality A
ward (2010). He was appointed as the President of Indonesian Mathematical
Society (2006-2008). He also plays a significant role in the development o
f mathematics in South East Asia region. He was the President of Southeast
Asian Mathematical Society (2014-2015)\, and served as a member of Scient
ific Committee of International Center for Pure and Applied Mathematics (C
IMPA) in 2009- 2020. \n\nHe has also contributed to the development of na
tional standards for education from primary school to higher education in
Indonesia as the member of the Board of National Standards for Education s
ince 2005 until 2015. He has been conducting various international confere
nces in mathematics and sciences. As of October 2022\, he has had the Scop
us h-index 19 with 175 research papers published in international journals
/proceedings with 1475 citations\, and produced more than 28 PhD graduates
.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sang-il Oum (Institute for Basic Science and KAIST\, South Korea)
DTSTART:20221111T020000Z
DTEND:20221111T033000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/22
DESCRIPTION:Title: Building the hierarchy of graph classes\nby Sang-il Oum (In
stitute for Basic Science and KAIST\, South Korea) as part of Combinatoric
s Today Series - ITB\n\n\nAbstract\nWe will survey the classification of g
raph classes in terms of the transductions in monadic second-order logic.
Blumensath and Courcelle (2010) characterized that every class of graphs i
s equivalent by transductions of the monadic second-order logic of the sec
ond kind to one of the following: class of all trees of height n for an in
teger n\, class of all trees\, class of all paths\, and class of all grids
. They conjectured that there is a similar linear hierarchy of graph class
es in terms of the monadic second-order logic of the first kind. We will d
iscuss how a recent theorem of the speaker with O-joung Kwon\, Rose McCart
y\, and Paul Wollan (2019) on the vertex-minor obstruction for shrub-depth
and a theorem of the speaker with Bruno Courcelle (2007) on graphs of lar
ge rank-width and logical expression of vertex-minors solve some subproble
ms of their conjecture.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicolas Trotignon (CNRS\, LIP\, ENS de Lyon\, France)
DTSTART:20221124T070000Z
DTEND:20221124T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/23
DESCRIPTION:Title: Widths and even-hole-free graphs\, a tour in structural graph t
heory\nby Nicolas Trotignon (CNRS\, LIP\, ENS de Lyon\, France) as par
t of Combinatorics Today Series - ITB\n\n\nAbstract\nEven-hole-free graphs
play an important role in the history of structural graph theory. In part
icular\, the attempts made by Cornuéjols\, Conforti and Vuskovic (among o
thers) to describe their structure in the 1990’s finally led to the righ
t conjecture about the structure of perfect graphs\, that was proved by Ch
udnovsky\, Robertson\, Seymour and Thomas in 2002. Today\, the structure o
f even-hole-free graphs and perfect graphs is still far from being fully u
nderstood. In this talk\, we will survey several attempts to study their s
tructure through classical width parameters\, such as treewidth. It turns
out that these attempts led to several conjectures and theorems about an
« induced subgraph » version of the celebrated grid theorem of Robertson
and Seymour.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Csilla Bujtás (University of Ljubljana\, Ljubljana\, Slovenia)
DTSTART:20221216T070000Z
DTEND:20221216T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/24
DESCRIPTION:Title: Triangle packings and coverings\nby Csilla Bujtás (Univers
ity of Ljubljana\, Ljubljana\, Slovenia) as part of Combinatorics Today Se
ries - ITB\n\n\nAbstract\nIn a graph $G$\, a triangle packing is a set of
pairwise edge-disjoint triangles\, and a triangle covering is a set of edg
es the removal of which makes the graph triangle-free. The maximum size $\
\nu_\\Delta(G)$ of a triangle packing and the minimum size $\\tau_\\Delta(
G)$ of a triangle covering clearly satisfies $\\tau_\\Delta\\left(G\\right
)\\le3\\nu_\\Delta(G)$. Tuza’s 40-year-old conjecture says that the stro
nger statement $\\tau_\\Delta\\left(G\\right)\\le2\\nu_\\Delta(G)$ is also
valid for all graphs. This relation holds with equality for the complete
graphs $K_4$ and $K_5$. Moreover\, for every positive $\\epsilon$ there ex
ists a $K_4$-free graph $G$ with $\\tau_\\Delta(G)\\ >\\ \\left(2-\\epsil
on\\right)\\nu_\\Delta(G)$.\nThe problem was extensively studied\, and the
inequality has been proved over several important graph classes. However\
, the general conjecture is still wide open. In the talk\, we survey the e
arlier results and discuss some recent ones concentrating on the class of
$K_4$-free graphs.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sanming Zhou (The University of Melbourne\, Australia)
DTSTART:20230217T070000Z
DTEND:20230217T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/25
DESCRIPTION:Title: Nowhere-zero 3-flows in vertex-transitive graphs\nby Sanmin
g Zhou (The University of Melbourne\, Australia) as part of Combinatorics
Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hilda Assiyatun (Institut Teknologi Bandung\, Indonesia)
DTSTART:20230331T070000Z
DTEND:20230331T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/26
DESCRIPTION:Title: On Ramsey-minimal graphs for combinations containing matchings\
, paths or stars\nby Hilda Assiyatun (Institut Teknologi Bandung\, Ind
onesia) as part of Combinatorics Today Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Kral (Masaryk University\, Czech Republic)
DTSTART:20230411T070000Z
DTEND:20230411T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/27
DESCRIPTION:Title: Quasirandom combinatorial structures\nby Daniel Kral (Masar
yk University\, Czech Republic) as part of Combinatorics Today Series - IT
B\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gordon Royle (University of Western Australia\, Australia)
DTSTART:20230608T070000Z
DTEND:20230608T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/28
DESCRIPTION:Title: Hamilton cycles in cubic and other graphs\nby Gordon Royle
(University of Western Australia\, Australia) as part of Combinatorics Tod
ay Series - ITB\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marien Abreu (Università degli Studi della Basilicata - Potenza\,
Italy)
DTSTART:20230707T070000Z
DTEND:20230707T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/29
DESCRIPTION:Title: Extending perfect matchings to Hamiltonian cycles\nby Marie
n Abreu (Università degli Studi della Basilicata - Potenza\, Italy) as pa
rt of Combinatorics Today Series - ITB\n\n\nAbstract\nA graph G\, admittin
g a perfect matching\, in which every perfect matching can be extended to
a Hamiltonian cycle is said to be Perfect-Matching-Hamiltonian (PMH for sh
ort). Consider the complete graph KG with the same vertex set as G. A perf
ect matching of KG is called a pairing of G. If for every paring M of G th
ere exists a perfect matching N of G such that M ∪ N is a hamiltonian cy
cle of KG we say that G is Pairing-Hamiltonian (PH for short). Note the su
btle difference between extending a pairing\, instead of a perfect matchin
g of G\, to a hamiltonian cycle using only edges of G. A PMH graph is thus
a special case of a PH graph. Results about these two families of graphs\
, although named differently\, date back to the 1970’s when Las Vergnas
and Haggkvist found Ore-type conditions for a graph to be PMH. Also\, all
hypercubes Qd\, for d ≥ 2 were shown to be PH\, by Fink in 2007\, thus p
roving a stronger version of a conjecture by Kreweras\, which stated that
hypercubes are PMH. Moreover cubic PH graphs were characterized\, in 2015\
, to be only K4\, K3\,3 and the cube Q3\, by Alahmadi et al. This seminar
contains resent results on PMH and PH graphs that can be summarized into:
(i) Graphs for which the line graph is PMH\, (ii) Cubic graphs which are
PMH\, and (iii) Products of graphs which are PH.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:M. Salman\, A.N. (Institut Teknologi Bandung\, Indonesia)
DTSTART:20230818T070000Z
DTEND:20230818T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/30
DESCRIPTION:Title: THE LOCATING RAINBOW CONNECTION NUMBER OF GRAPHS\nby M. Sa
lman\, A.N. (Institut Teknologi Bandung\, Indonesia) as part of Combinator
ics Today Series - ITB\n\n\nAbstract\nLet G=(V(G)\,E(G)) be a finite and c
onnected graph of order n≥2. In 2021\, we introduced the locating rainbo
w connection number of G\, denoted by rvcl(G)\, that combines the concepts
of the rainbow vertex coloring and the partition dimension of a graph. In
this talk\, we present some results about it. Firstly\, we provide both a
lower bound and an upper bound for rvcl(G). Then\, we characterize the gr
aphs G with rvcl(G)=2 or rvcl(G)=n. Furthermore\, we determine the locati
ng rainbow connection number of some graph classes\, including complete gr
aphs\, paths\, stars\, regular bipartite graphs\, and trees. Additionally\
, we present the locating rainbow connection number of amalgamation of com
plete graphs. In the last section\, we present some open problems.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jose Maria Balmaceda (University of the Philippines Diliman\, Phil
ippines)
DTSTART:20230930T070000Z
DTEND:20230930T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/31
DESCRIPTION:Title: Association Schemes and Related Structures\nby Jose Maria B
almaceda (University of the Philippines Diliman\, Philippines) as part of
Combinatorics Today Series - ITB\n\n\nAbstract\nAssociation schemes\, firs
t introduced in the 1950s by R.C. Bose and T. Shimamoto in the design of e
xperiments\, are combinatorial objects that were used by P. Delsarte in th
e 1970s to study coding theory and design theory. Today they are important
structures in algebraic combinatorics and the theory offers a unifying fr
amework for the study of various objects such as finite geometries\, graph
s with high symmetry\, codes\, and designs. We give an introduction to the
theory of association schemes\, including its sources and connections wit
h other branches of math. We also present some recent work on the extensio
n of the classical theory to association schemes on triples\, where underl
ying relations and corresponding adjacency algebras are ternary instead of
binary.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mihyun Kang (Graz University of Technology\, Institute of Discret
e Mathematics\, Graz\, Austria)
DTSTART:20231020T070000Z
DTEND:20231020T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/32
DESCRIPTION:Title: Topological aspects of random graphs\nby Mihyun Kang (Graz
University of Technology\, Institute of Discrete Mathematics\, Graz\, Aus
tria) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nIn this t
alk we will briefly overview classical results on Erdos-Renyi random graph
s and discuss various topological aspects of random graphs. We are interes
ted in the following questions: How does the genus of a random graph chang
e as the edge density increases? How does a topological constraint (such a
s being planar) influence the global and local structure of a random graph
(such as the order of the largest component and local weak limits)?\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kiki Ariyanti Sugeng (Universitas Indonesia\, Indonesia)
DTSTART:20231103T070000Z
DTEND:20231103T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/33
DESCRIPTION:Title: On Modular Irregularity Strength for Some Families of Graphs\nby Kiki Ariyanti Sugeng (Universitas Indonesia\, Indonesia) as part of
Combinatorics Today Series - ITB\n\n\nAbstract\nLet consider a simple and
finite graph $G$ with order $n$. Motivated by irregular graph\, Chartrand
{\\it et al.} in 1998 defined an irregular labeling as an edge $k$-labelin
g $f: E(G) \\to \\{1\, 2\, ... \, k\\}$\, for a positive integer $k$\, so
that every vertex has different weight. The sum of all edge labels which
is incidence to $v$ is called the vertex weight of $v$. What are we lookin
g for is the minimum number $k$ for this kind of labeling. The minimum num
ber of $k$ for such labeling is called the irregularity strength of a grap
h G and is denoted by s(G). In 2020\, Baca et al.introduced the variation
of irregular labeling in modular version. Modular irregular labeling of a
graph $G$ is an edge $k$-labeling $f: E(G)\\to \\{1\,2\,...\,k\\}$ such th
at the modular weight\, which is the sum of all edges that incident to $v$
modulo $n$\, of all vertices are all different. For the case of modular\,
the modular irregularity strength of a graph $G$\, notated by ms($G$)\, i
s a minimum number $k$ such that a graph $G$ has modular irregular labelin
g with the largest label $k$. In this talk\, we give the survey on which f
amilies of graphs that have been proved that have modular irregularity lab
eling.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sandi Klavzar (University of Ljubljana\, Slovenia)
DTSTART:20231117T070000Z
DTEND:20231117T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/34
DESCRIPTION:Title: Visibility Concepts in Graph Theory\nby Sandi Klavzar (Univ
ersity of Ljubljana\, Slovenia) as part of Combinatorics Today Series - IT
B\n\n\nAbstract\nRecently\, the field of computer science has seen a need
to explore the concept of visibility in graph theory. The variety of relat
ed concepts can be described as follows. Given a connected graph $G$ and a
set of vertices $X\\subseteq V(G)$\, two vertices $x\,y\\in V(G)$ are cal
led to be $X$-\\emph{visible} if there is a shortest $x\,y$-path (also cal
led geodesic) whose interior vertices do not belong to $X$. With this idea
in mind\, we say that $X$ is \n \n\n(1) a mutual-visibility set: if any t
wo vertices of $X$ are $X$-visible\; \n(2) an outer mutual-visibility set:
if any two vertices $x\,y\\in X$ and any two vertices $x\\in X$ and $y\\i
n \\overline{X}$ are $X$-visible\; \n(3) a dual mutual-visibility set: if
any two vertices $x\,y\\in X$ and any two vertices $x\,y\\in \\overline{X}
$ are $X$-visible\; and \n(4) a total mutual-visibility set: if any two ve
rtices $x\,y\\in V(G)$ are $X$-visible.\n\nIn this talk\, we will present
some results on these concepts. We will pay special attention to Hamming g
raphs\, since problems on them give rise to unexpected connections with so
me classical mathematical problems and concepts.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vida Dujmovic (University of Ottawa\, Canada)
DTSTART:20231208T120000Z
DTEND:20231208T133000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/35
DESCRIPTION:Title: Proof of the Clustered Hadwiger Conjecture\nby Vida Dujmovi
c (University of Ottawa\, Canada) as part of Combinatorics Today Series -
ITB\n\n\nAbstract\nHadwiger's Conjecture asserts that every Kh-minor-free
graph is properly (h-1)-colourable. We prove the following improper analog
ue of Hadwiger's Conjecture: for fixed h\, every Kh-minor-free graph is (h
-1)-colourable with monochromatic components of bounded size. The number o
f colours is best possible regardless of the size of monochromatic compone
nts. It solves an open problem of Edwards\, Kang\, Kim\, Oum and Seymour [
SIAM J. Disc. Math. 2015]\, and concludes a line of research initiated in
2007.\n\n\nThis is joint work with Louis Esperet\, Pat Morin and David R.
Wood.\n\nVida Dujmovic is a University Research Chair and Professor of Com
puter Science at University of Ottawa. Her main research areas are graph t
heory (geometric and structural). She has published over 80 journal papers
. \n\nShe is a recipient of the Early Researcher Award by the Ontario gov
ernment\, Glinski Award for Excellence in Research by the University of Ot
tawa. She is an invited speaker at the 2024 European Congress of Mathemat
icians\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Djoko Suprijanto (Institut Teknologi Bandung)
DTSTART:20240224T070000Z
DTEND:20240224T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/36
DESCRIPTION:Title: Cyclic codes over finite rings and their generalizations: Struc
tural properties and applications\nby Djoko Suprijanto (Institut Tekno
logi Bandung) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nC
yclic codes are one of the most widely studied families of codes\, both be
cause of their rich mathematical structure and their use in applications.
Cyclic codes have also been generalized in numerous ways\, including negac
yclic codes\, constacyclic codes\, and skew cyclic codes with derivation.\
n\nIn this talk\, we will discuss recent developments in the study of cycl
ic codes and their generalization\, with a focus on what we call two-step
generalizations of cyclic codes\, or skew cyclic codes with derivation.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Charles Joseph Colbourn (Arizona State University\, USA)
DTSTART:20240511T020000Z
DTEND:20240511T033000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/37
DESCRIPTION:Title: Popularity Labellings for Steiner Systems\nby Charles Josep
h Colbourn (Arizona State University\, USA) as part of Combinatorics Today
Series - ITB\n\n\nAbstract\nSteiner systems and their duals are widely us
ed for data layout in distributed storage systems. In practice\, mapping d
ata items to storage units often ignores the long-term popularity of the i
tems\, which can cause a significant imbalance in traffic to storage units
. In addressing popularity\, two main problems arise:\n\n1. Label the v po
ints of a design with {0\, 1\, ...\, v−1}\, computing each block sum as
the sum of the labels of points contained in that block. The block differe
nce sum is the difference between the largest and smallest block sums. Pop
ularity point labelling seeks to minimize the block difference sum.\n\n2.
Label the b blocks of a design with {0\, 1\, ...\, b − 1}\, computing e
ach point sum as the sum of the labels of blocks containing that point. Th
e point difference sum is the difference between the largest and smallest
point sums. Popularity block labelling seeks to minimize the point differe
nce sum.\n\nWe first derive lower bounds on the difference sums for Steine
r systems S(t\, k\, v). We then outline constructions that yield ‘small
’ difference sums. Finally\, we mention some open problems that deserve
more attention.\n\nBrief biography: Charles J. Colbourn was born in Toront
o in 1953. He completed his B.Sc. (Toronto)\, M.Math. (Waterloo)\, and Ph
.D. (Toronto)\, all in computer science. He held faculty positions at the
University of Saskatchewan\, the University of Waterloo\, and the Univers
ity of Vermont\, and has been a Professor of Computer Science and Engineer
ing at Arizona State University since 2001.\n\nHe is co-editor of the Hand
book of Combinatorial Designs and author of Triple Systems and The Combina
torics of Network Reliability. He is an editor-in-chief of the Journal of
Combinatorial Designs. His research concerns applications of combinatori
al designs in networking\, computing\, and communications.\n\nFor more inf
ormation\, see https://www.public.asu.edu/}$\\sim${\\tt ccolbou/\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cristina Dalfo (Universitat de Lleida Igualada (Barcelona)\, Catal
onia)
DTSTART:20241125T070000Z
DTEND:20241125T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/38
DESCRIPTION:Title: Combined voltage assignments\, factored lifts\, and their spect
ra\nby Cristina Dalfo (Universitat de Lleida Igualada (Barcelona)\, Ca
talonia) as part of Combinatorics Today Series - ITB\n\n\nAbstract\nIn thi
s talk\, we introduce the concept of factored lift\, associated with a com
bined voltage graph\, as a generalization of the lift graph. We present a
new method for computing all the eigenvalues and eigenspaces of factored l
ifts. The underlying group can be Abelian or not Abelian\, and we will dea
l with both cases.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hajime Tanaka (Tohoku University\, Japan)
DTSTART:20241104T090000Z
DTEND:20241104T103000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/39
DESCRIPTION:Title: Linear/semidefinite programming techniques in combinatorics
\nby Hajime Tanaka (Tohoku University\, Japan) as part of Combinatorics To
day Series - ITB\n\n\nAbstract\nLinear/semidefinite programming techniques
have been useful in proving theorems in various areas of combinatorics\,
such as coding theory and extremal set theory. While they do not always le
ad to the best versions\, these techniques provide attractive applications
of algebraic graph theory.\n\nIn this talk\, I will begin with the fundam
ental results by Delsarte and Lovász in the 1970's and then move on to di
scussing some of the most successful applications\, an example of which is
Wilson's 1984 proof of the Erdős-Ko-Rado theorem. I will also mention re
cent joint work with Norihide Tokushige on a measure version of the q-anal
og of this theorem.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ismael G. Yero (University of Cadiz Algeciras Campus\, Spain)
DTSTART:20241209T090000Z
DTEND:20241209T103000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/40
DESCRIPTION:Title: Mobile Mutual-Visibility Sets in Graphs\nby Ismael G. Yero
(University of Cadiz Algeciras Campus\, Spain) as part of Combinatorics T
oday Series - ITB\n\n\nAbstract\nGiven a connected graph $G$\, a mutual-vi
sibility set of G is a set of vertices $S \\subset V(G)$ such that for eac
h two vertices $x\,y$ in $S$ there is a shortest $(x\,y)$-path whose inter
ior vertices are not in $S$. Assume now that in each vertex of a mutual-vi
sibility set $S$ a robot is placed\, and consider that they can move from
one vertex to a neighboring one\, so that at each stage only one robot mov
es to a neighbor of it. The set $S$ is called a mobile mutual-visibility s
et of $G$\, if there exists a sequence of moves of the robots such that ea
ch vertex of $G$ is visited by at least one robot\, while all the time\, t
he set of vertices occupied by the robots is a mutual-visibility set of $G
$. The mobile mutual-visibility number of $G$ is the cardinality of a larg
est mobile mutual-visibility set of $G$. Several contributions in these n
otions shall be presented in this talk. The results of the work are from t
he article [M. Dettlaff\, M. Lemanska\, J. A. Rodriguez-Velazquez\, I. G.
Yero\, Mobile mutual-visibility sets in graph. Manuscript\, (2024)].\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gabriela Araujo-Pardo (Instituto de Matemáticas\, Universidad Nac
ional Autónoma de Mexico\, Mexico)
DTSTART:20240629T020000Z
DTEND:20240629T033000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/41
DESCRIPTION:Title: On mixed cages\nby Gabriela Araujo-Pardo (Instituto de Mate
máticas\, Universidad Nacional Autónoma de Mexico\, Mexico) as part of C
ombinatorics Today Series - ITB\n\n\nAbstract\nA mixed regular graph is a
graph with both edges and arrows\, where every vertex has the same number
of edges and it has the same number of inside and exit arrows. A cycle on
a mixed graph is a cycle with edges and arrows with the property that all
arrows are traversed in the same direction. A mixed cage is a mixed regula
r graph with some fixed girth (the smallest length of any cycle) and minim
um order. These graphs were introduced in 2019 by Araujo-Pardo\, Hernánde
z\, and Montellano-Ballesteros. From that moment on\, different authors ha
ve worked on this topic\, the last published work on this topic was given
by Exoo in 2023. In this talk\, I will give a resume about the state of th
e art of mixed graphs until this moment. Moreover\, I will talk about some
recent work that I have done with Lydia Mendoza.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Slamin (Universitas Jember\, Indonesia)
DTSTART:20250210T090000Z
DTEND:20250210T103000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/42
DESCRIPTION:Title: The Role of Graph Theory in Machine Learning\nby Slamin (Un
iversitas Jember\, Indonesia) as part of Combinatorics Today Series - ITB\
n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sylwia Cichacz (AGH University in Cracow\, Poland)
DTSTART:20250320T070000Z
DTEND:20250320T083000Z
DTSTAMP:20260422T225756Z
UID:CombinTodaySeries/43
DESCRIPTION:Title: APPLICATION OF ZERO-SUM SETS IN MAGIC-TYPE AND ANTIMAGIC-TYPE G
RAPH LABELING\nby Sylwia Cichacz (AGH University in Cracow\, Poland) a
s part of Combinatorics Today Series - ITB\n\n\nAbstract\nLet $(\\Gamma\,+
)$ be an Abelian group. A subset $S$ of $\\Gamma$ is called a \\textit{zer
o-sum subset} if $\\sum_{a\\in S} a=0$. One of the key topics in zero-sum
theory is the study of disjoint zero-sum subsets in $\\Gamma$. This approa
ch was inspired by Steiner triples research and started by Skolem. \\\\\n\
nInterestingly\, certain magic-type and antimagic-type graph labelings are
closely related to disjoint zero-sum subsets in $\\Gamma$. In this talk\,
we will explore some of these connections.\n
LOCATION:https://researchseminars.org/talk/CombinTodaySeries/43/
END:VEVENT
END:VCALENDAR