Programme of the Pure Mathematics Colloquium
The colloquium takes place on Thursdays at
4pm in Theatre C of the
Mathematical Institute (unless indicated otherwise).
The schedule for Semester 2 of 2017-18 is:
8th Feb, 2018:
Tadahiro Oh (Edinburgh)
Title: On singular stochastic dispersive PDEs
In this talk, I will go over some of the recent developments on nonlinear dispersive PDEs, such as the nonlinear Schroedinger equations (NLS) and nonlinear wave equations (NLW), with rough and random data and/or forcing. In particular, taking the stochastic NLS and the stochastic nonlinear heat equations as examples, I will describe the difference between the dispersive and parabolic problems from the viewpoint of critical regularities, etc. If time permits, I will also discuss some recent development for the stochastic NLW.
15th Feb, 2018:
Tom Coleman (St Andrews)
Title: Permutation monoids and MB-homogeneous structures
There is a widely studied connection between subgroups of the infinite symmetric group and automorphisms of first-order structures; in particular, homogeneous structures (as characterised in the celebrated theorem of Fraisse) provide examples of interesting infinite permutation groups. This connection can be generalised in a surprising fashion, as there exist submonoids of the infinite symmetric group that are not necessarily groups; these are called permutation monoids. Much like the group case, there is a correspondence between permutation monoids and bimorphism monoids (monoids of bijective endomorphisms) of first-order structures.
In this talk, I will explore this connection, introduce the idea of an MB-homogeneous structure and characterise these by demonstrating a Fraisse-like theorem. I will then go on to examine MB-homogeneous graphs in more detail, leading to some surprising results.
The material in this talk almost wholly consists of work done during my PhD, and is joint with David Evans (Imperial) and Bob Gray (UEA).
22nd Feb, 2018:
Dane Flannery (Galway)
Title: Algebraic design theory
Algebraic perspectives and techniques have become increasingly
prevalent in combinatorial design theory. The designs of interest can
be viewed as square matrices whose rows (or columns) taken pairwise
obey a fixed constraint depending on the matrix size and coefficient
ring. Hadamard matrices and their generalisations are important
examples; the constraint in these cases is orthogonality.
The literature on Hadamard matrices is immense, covering numerous
applications in areas such as signal processing, cryptography, and
The algebraic approach has been especially successful in solving
existence and classification problems for `cocyclic' designs, which
are defined via certain regular subgroups of their automorphism groups.
The pairwise row/column constraint for cocyclic designs translates to
a simpler balance condition (e.g., a cocyclic matrix is Hadamard if
and only if all non-initial row sums are zero).
We present a survey of algebraic design theory, emphasizing some key
results and open problems. In particular, we mention recent work
extending the notion of cocyclic design when necessary restrictions
on matrix size are modified (e.g., what is the analogue of cocyclic
Hadamard matrix when the size is even but not divisible by 4?). This arose
from considerations of the maximal determinant problem originally posed
8th Mar, 2018:
Maura Paterson (Birkbeck) - this talk was originally scheduled for 1st Mar, but moved due to snow
Title: Recent directions in Private Information Retrieval
Private Information Retrieval (PIR) is a technique that allows a user to obtain a record from a database without the database owner learning which record the user wishes to access. One way to achieve this is for the user to download the entire database. However, it is clearly desirable to construct PIR schemes in which this is not necessary. In the unconditionally secure model (where we make no assumptions about the computational power of the database owners) interesting combinatorial problems arise naturally from the study of these schemes as we consider trade-offs between properties such as the size of the queries to the database, the number of bits downloaded from the database and the number of bits required for storing the database. In this talk we will provide a background survey on unconditionally secure PIR before discussing some newer directions in the study of these schemes. https://arxiv.org/abs/1609.07027
15th Mar, 2018: Colloquium cancelled
5th Apr, 2018:
Jess Enright (Edinburgh)
Title: Changing times in temporal graphs
Temporal graphs (in which edges are active only at specified time steps) are an increasingly important and popular model for a wide variety of natural and social phenomena. I'll talk a bit about what's been going on in the world of temporal graphs, and then go on to the idea of graph modification in a temporal setting.
Motivated by cows and rumours, I'll talk about a particular modification problem in which we assign times to edges so as to maximise or minimise reachability sets within a temporal graph. I'll mention an assortment of complexity results on these problems, showing that they are hard under a disappointingly large variety of restrictions. In particular, if edges can be grouped into classes that must be assigned the same time, then the problem is hard even on directed acyclic graphs when both the reachability target and the classes of edges are of constant size, as well as on an extremely restrictive class of trees. For fans of parameterised complexity, I'll note that one version of the problem is W-hard when parameterised by the vertex cover number of the instance graph. The situation is slightly better if each edge is active at a unique timestep - in some very restricted cases the problem is solvable in polynomial time. (Joint work with Kitty Meeks.)
If you're not a lifelong fan of graphs or computational complexity, never fear! I will try to make this talk as enjoyable and accessible as possible, and will be sure to point out the important bits. There will probably be at least one picture of livestock.
12th Apr, 2018:
John Mackay (Bristol)
19th Apr, 2018:
Marianne Johnson (Manchester)
26th Apr, 2018:
Fenny Smith (BSHM)
Title: So where did our numbers come from anyway?
Past colloquia can be found here.
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