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October 2019

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Casey Tompkins, Extremal problems for Berge hypergraphs

Speaker

October 1 Tuesday @ 4:30 PM - 5:30 PM
Room B232, IBS (기초과학연구원)

Given a graph $G$, there are several natural hypergraph families one can define. Among the least restrictive is the family $BG$ of so-called Berge copies of the graph $G$. In this talk, we discuss Turán problems for families $BG$ in $r$-uniform hypergraphs for various graphs $G$. In particular, we are interested in general results in two settings: the case when $r$ is large and $G$ is any graph where this Turán number is shown to be eventually subquadratic, as well…

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Alexandr V. Kostochka, On Ramsey-type problems for paths and cycles in dense graphs

Speaker

Alexandr V. Kostochka
University of Illinois at Urbana-Champaign
https://faculty.math.illinois.edu/~kostochk/
October 8 Tuesday @ 4:30 PM - 5:30 PM
Room 1501, Bldg. E6-1, KAIST

A well-known Ramsey-type puzzle for children is to prove that among any 6 people either there are 3 who know each other or there are 3 who do not know each other. More generally, a graph $G$ arrows a graph $H$ if for any coloring of the edges of $G$ with two colors, there is a monochromatic copy of $H$. In these terms, the above puzzle claims that the complete $6$-vertex graph $K_6$ arrows the complete $3$-vertex graph $K_3$. We consider sufficient…

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Alexandr V. Kostochka, Reconstructing graphs from smaller subgraphs

Speaker

Alexandr V. Kostochka
University of Illinois at Urbana-Champaign
https://faculty.math.illinois.edu/~kostochk/
October 10 Thursday @ 4:30 PM - 5:30 PM
Room B232, IBS (기초과학연구원)

A graph or graph property is $\ell$-reconstructible if it is determined by the multiset of all subgraphs obtained by deleting $\ell$ vertices. Apart from the famous Graph Reconstruction Conjecture, Kelly conjectured in 1957 that for each $\ell\in\mathbb N$, there is an integer $n=n(\ell)$ such that every graph with at least $n$ vertices is $\ell$-reconstructible. We show that for each $n\ge7$ and every $n$-vertex graph $G$, the degree list and connectedness of $G$ are $3$-reconstructible, and the threshold $n\geq 7$ is sharp for both properties.‌ We…

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Zi-Xia Song (宋梓霞), Ramsey numbers of cycles under Gallai colorings

Speaker

October 15 Tuesday @ 4:30 PM - 5:30 PM
Room B232, IBS (기초과학연구원)

For a graph $H$ and an integer $k\ge1$, the $k$-color Ramsey number $R_k(H)$ is the least integer $N$ such that every $k$-coloring of the edges of the complete graph $K_N$ contains a monochromatic copy of $H$. Let $C_m$ denote the cycle on $m\ge4 $ vertices. For odd cycles, Bondy and Erd\H{o}s in 1973 conjectured that for all $k\ge1$ and $n\ge2$, $R_k(C_{2n+1})=n\cdot 2^k+1$. Recently, this conjecture has been verified to be true for all fixed $k$ and all $n$ sufficiently large…

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Joonkyung Lee (이준경), On some properties of graph norms

Speaker

Joonkyung Lee (이준경)
Department of Mathematics, University of Hamburg, Germany
https://sites.google.com/site/joonkyungleemaths/
October 22 Tuesday @ 4:30 PM - 5:30 PM
Room B232, IBS (기초과학연구원)

For a graph $H$, its homomorphism density in graphs naturally extends to the space of two-variable symmetric functions $W$ in $L^p$, $p\geq e(H)$, denoted by $t_H(W)$. One may then define corresponding functionals $\|W\|_{H}:=|t_H(W)|^{1/e(H)}$ and $\|W\|_{r(H)}:=t_H(|W|)^{1/e(H)}$ and say that $H$ is (semi-)norming if $\|.\|_{H}$ is a (semi-)norm and that $H$ is weakly norming if $\|.\|_{r(H)}$ is a norm. We obtain some results that contribute to the theory of (weakly) norming graphs. Firstly, we show that 'twisted' blow-ups of cycles, which include…

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Extremal and Structural Graph Theory (2019 KMS Annual Meeting)

October 26 Saturday - October 27 Sunday
Room 426, Hong-Mun Hall, Hongik University, Seoul

Focus Session @ 2019 KMS Annual MeetingA focus session "Extremal and Structural Graph Theory" at the 2019 KMS Annual Meeting is organized by Sang-il Oum. URL: http://www.kms.or.kr/meetings/fall2019/SpeakersIlkyoo Choi (최일규), Hankuk University of Foreign StudiesKevin Hendrey, IBS Discrete Mathematics GroupPascal Gollin, IBS Discrete Mathematics GroupJaehoon Kim (김재훈), KAISTRingi Kim (김린기), KAISTSeog-Jin Kim (김석진), Konkuk UniversityO-joung Kwon (권오정), Incheon National University / IBS Discrete Mathematics GroupZi-Xia Song (宋梓霞), University of Central FloridaCasey Tompkins, IBS Discrete Mathematics GroupSchedulesSlot A: October 26, 2019 Saturday, 9:00am-10:15amSeog-Jin KimKevin HendreyIlkyoo ChoiSlot…

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Pascal Gollin, A Cantor-Bernstein-type theorem for spanning trees in infinite graphs

Speaker

Pascal Gollin
IBS Discrete Mathematics Group
https://dimag.ibs.re.kr/home/gollin/
October 29 Tuesday @ 4:30 PM - 5:30 PM
Room B232, IBS (기초과학연구원)

Given a cardinal $\lambda$, a $\lambda$-packing of a graph $G$ is a family of $\lambda$ many edge-disjoint spanning trees of $G$, and a $\lambda$-covering of $G$ is a family of spanning trees covering $E(G)$.We show that if a graph admits a $\lambda$-packing and a $\lambda$-covering  then the graph also admits a decomposition into $\lambda$ many spanning trees. In this talk, we concentrate on the case of $\lambda$ being an infinite cardinal. Moreover, we will provide a new and simple proof for a theorem…

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The 2nd East Asia Workshop on Extremal and Structural Graph Theory

October 31 Thursday - November 4 Monday
UTOP UBLESS Hotel, Jeju, Korea (유탑유블레스호텔제주)

The 2nd East Asia Workshop on Extremal and Structural Graph Theory is a workshop to bring active researchers in the field of extremal and structural graph theory, especially in the East Asia such as China, Japan, and Korea.DateOct 31, 2019 (Arrival Day) - Nov 4, 2019 (Departure Day)Venue and Date1st floor  Diamond HallUTOP UBLESS Hotel, Jeju, Korea (유탑유블레스호텔제주) Address: 502 Johamhaean-ro, Jocheon-eup, Jeju, Korea (제주특별자치도 제주시 조천읍 조함해안로 502) We plan to support the accommodation for invited participants. The UTOP…

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November 2019

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Sun Kim (김선), Two identities in Ramanujan’s Lost Notebook with Bessel function series

Speaker

November 5 Tuesday @ 4:30 PM - 5:30 PM
Room 1401, Bldg. E6-1, KAIST

On page 335 in his lost notebook, Ramanujan recorded without proofs two identities involving finite trigonometric sums and doubly infinite series of Bessel functions. We proved each of these identities under three different interpretations for the double series, and showed that they are intimately connected with the classical circle and divisor problems in number theory. Furthermore, we established many analogues and generalizations of them. This is joint work with Bruce C. Berndt and Alexandru Zaharescu.

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Combinatorial and Discrete Optimization (2019 KSIAM Annual Meeting)

November 8 Friday @ 12:00 PM - November 9 Saturday @ 7:00 PM
Venezia Hotel & Resort Yeosu, Yeosu, Korea (여수 베네치아 호텔) 

Special Session @ 2019 KSIAM Annual MeetingA special session on "Combinatorial and Discrete Optimization" at the 2019 KSIAM Annual Meeting is organized by Dabeen Lee. URL: https://www.ksiam.org/conference/84840fb6-87b0-4566-acc1-4802bde58fbd/welcomeDateNov 8, 2019 – Nov 9, 2019 Address: 61-13 Odongdo-ro, Sujeong-dong, Yeosu-si, Jeollanam-do (전남 여수시 오동도로 61-13)VenueVenezia Hotel & Resort Yeosu, Yeosu, Korea (여수 베네치아 호텔)  Address: 61-13 Odongdo-ro, Sujeong-dong, Yeosu-si, Jeollanam-do (전남 여수시 오동도로 61-13)SpeakersHyung-Chan An (안형찬), Yonsei UniversityTony Huynh, Monash UniversityDong Yeap Kang (강동엽), KAIST / IBS Discrete Mathematics GroupDabeen Lee (이다빈), IBS Discrete…

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