12 JUN 2025
14:00 - 16:00

The automorphism group of a countable first-order structure naturally carries the topology of pointwise convergence. In certain cases, this topology can be used to recover/reconstruct the structure up to bi-interpretability. However, it is not the only group topology of interest. In this talk, we explore various group topologies on automorphism groups - particularly minimal group topologies - with a special emphasis on the Zariski topology. This is joint work with Javier de la Nuez González.

Zoom room information:
https://us06web.zoom.us/j/81916335336?pwd=5zQT4lutMiBoY5Xp1pkFGtbqiaGozg.1
Meeting ID: 819 1633 5336
Passcode: 559618
Venue: Niavaran, Khosrovshahi Lecture Hall

11 JUN 2025
14:00 - 15:00

Rank aggregation is a well studied algorithmic problem where, given a set of input preference lists over a set of items, the objective is to compute a single ranking that best summarizes the individual lists. The problem has numerous applications, e.g., in social choice, recommendation systems, and information retrieval. In this talk we tackle this problem in the dynamic setting, and present a practically efficient 2-approximation algorithm with near linear update time for the problem. Based on joint work with Alireza Zarei and Morteza Alimi.

Zoom room information:
https://us06web.zoom.us/j/84906984159?pwd=BCWaIbXBuku3A5I84zNg9mHFxVZjXD.1
Meeting ID: 849 0698 4159
Passcode: 362880
Venue: Niavaran, Khosrovshahi Lecture Hall

28 MAY 2025
17:30 - 19:00

In this talk we study some properties of the Hadamard products of symbolic powers, in particular, if for points $P, Qin {mathbb{P}}^2$, we get $I(P)^m*I(Q)^n= I(P*Q)^{m+n−1}$. We obtain different results according to the number of zero coordinates in $P$ and $Q$. Successively, we define the so called Hadamard fat grids, which are the result of the Hadamard product of two sets of collinear points with given multiplicites. The most important invariants of Hadamard fat grids, as minimal resolution, Waldschmidt constant and resurgence, are then computed using also tools and known results in ${mathbb{P}}^1 imes{mathbb{P}}^1$. (This is a joint work with I. Bahmani Jafarloo, C. Bocci, G. Malara).

Venue: online
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Meeting ID: 9086116889
Passcode: 362880
Website: http://math.ipm.ac.ir/agnt/
Venue: , (Online)

28 MAY 2025
14:00 - 15:00

In this talk we introduce the asymptotic almost sure expansion lower bounds of random d-regular graphs in the uniform model and provide improvements for d ≥ 4 through solving a parametrized relaxation of the expansion lower bound problem. As a concrete consequence of our main result, we prove that for large degrees d ≥ 6 � 10^4 the optimal a.a.s. expansion lower bound of d-regular graphs is greater than d/2‎ - ‎0.7942^{-} √d which is an improvement over the long-standing a.a.s. lower bound d/2‎ - ‎0.8326^{-} √d provided by B. Bollob�as (1988). Also, for small degrees, we apply our main result along with an a.a.s. upper bound of R. Lyons (2017) for bisection width to explicitly obtain improvements on known a.a.s. expansion lower bounds for small degrees 4 ≤ d ≤ 10. In particular, we report the lower bounds 0.4452 for d = 4, 0.7494 for d = 5 and 1.0584 for d = 6 that improve the best previously known results of A. Amit-N. Linial (2006).
These results are part of a joint collaboration with Dr. Amir Daneshgar.

Zoom room information:
https://us06web.zoom.us/j/84906984159?pwd=BCWaIbXBuku3A5I84zNg9mHFxVZjXD.1
Meeting ID: 849 0698 4159
Passcode: 362880
Venue: Niavaran, Lecture Hall 2

21 MAY 2025
16:00 - 17:00

The emergence of AI, particularly large language models (LLMs), has dramatically reshaped the requirements for error-correcting codes, particularly in the realm of memory I/O during training. Massive data transfers involved in training LLMs necessitate extremely robust error correction to prevent costly retraining scenarios triggered by undetected errors (Silent Data Corruption). Traditional iterative decoding techniques are inadequate due to their latency constraints, pushing the field towards combinational logic implementations capable of achieving multiple-error correction under extremely tight latency budgets. Algebraic codes, which once seemed to have lost ground to iterative decoding algorithms, are experiencing a renaissance driven by these stringent AI-driven performance demands. By exploiting deep results from algebra, notably Galois theory, algebraic codes are now being implemented in fully combinational hardware circuits that offer both the necessary decoding speed and robust error-correction guarantees. This development underscores algebraic coding theory?s renewed relevance and critical importance for future high-performance AI systems​.

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Venue: Niavaran, Lecture Hall 1

15 MAY 2025
14:00 - 16:00

An imaginary sort of a first-order structure is a possible universe of an interpretable structure. The significance of imaginary sorts was established in the abstract setting of Classification Theory by Shelah, where all notions of stability theory, especially algebraic closure, were interpreted with imaginary sorts taken into account. Imaginaries were studied for specific theories by Poizat who showed that algebraically closed fields and differentially closed fields eliminate imaginaries, i.e. each imaginary sort is in definable bijection with a definable set of n-tuples. In valued fields imaginary sorts differ qualitatively from definable sets; an example is the value group. In this case it is a question of finding a useful basis for the imaginary sorts, meaning that every imaginary sort can be embedded into a product of basis elements. A basis for imaginary sorts for algebraically closed valued fields was given by Haskell-Hrushovski-Macpherson. Rideau-Hrushovski-Martin, and more recently Hils-Rideau-Kikuchi, proved that for the field of $p$-adic numbers the $p$-adic lattices provide a basis for imaginary sorts.
In this talk I will describe joint work with Ehud Hrushovski which gives a description of imaginary sorts and their basis for products and restricted products of structures in terms of a basis for imaginary sorts for the factors. In 1959 Feferman and Vaught proved that the theory of a product is determined by the theory of the factors and the theory of the Boolean algebra of subsets of the index set. This yields decidability results and descriptions of definable sets for products in terms of the factors. Our results show that imaginaries also admit a description relative to the factors. The proofs use tools from geometric stability theory including liaison groups, and descriptive set theory of smooth Borel equivalence relations, including a dichotomy theorem due to Harrington-Kechris-Louveau and Glimm-Efros. As an application, we describe a basis for the imaginary sorts for the ring of adeles of rational numbers in terms of the family of $p$-adic lattices for �almost all� $p$, and prove weak elimination of imaginaries for the adeles in these sorts.

Joint work with: Ehud Hrushovski
Zoom room information:
https://us06web.zoom.us/j/81916335336?pwd=5zQT4lutMiBoY5Xp1pkFGtbqiaGozg.1
Meeting ID: 819 1633 5336
Passcode: 559618
Venue: Niavaran, Lecture Hall 1