 CARMA COLLOQUIUM
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Groups, machines, algae and trees
 Location: Room V205, Mathematics Building (Callaghan Campus) The University of Newcastle
 Time and Date: 4:00 pm, Tue, 4^{th} Apr 2017
 Abstract:
In a way, mathematics can be seen as a language game, where we use symbols, together with some rewriting rules, to represent objects we are interested in and then ask what can be said about the sequences of symbols (languages) that capture certain phenomena. For example, given a group G with generators a and b, can we recognise (using a computer) the sequences of generators that correspond to nontrivial elements of G? If yes, how strong computer do we need, i.e. how complicated is the language we are studying?
There is a natural duality between various types of computational models and classes of languages that can be recognised by them. Until recently most problems/languages in group theory were classified within the Chomsky hierarchy, but there are more computational models to consider. In the talk I will briefly introduce Lsystems, a family of classes of languages originally developed to model growth of algae, and show that the coword problem in Grigorchuk's group, a group of particularly nice transformations of infinite binary tree, can be seen as a language corresponding to a fairly simple Lsystem.
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 CARMA GROUP THEORY RHD MEETING
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Galois theory
 Location: Room V206, Mathematics Building (Callaghan Campus) The University of Newcastle
 Time and Date: 11:00 am, Thu, 23^{rd} Feb 2017
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 CARMA GROUP THEORY RHD MEETING
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Galois theory for infinite algebraic extensions
 Location: Room V205, Mathematics Building (Callaghan Campus) The University of Newcastle
 Time and Date: 11:00 am, Fri, 17^{th} Feb 2017
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 CARMA GROUP THEORY RHD MEETING
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Separating cyclic subgroups in graph products
 Location: Room V205, Mathematics Building (Callaghan Campus) The University of Newcastle
 Time and Date: 11:00 am, Thu, 17^{th} Nov 2016
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 CSSE SEMINAR
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Enhancing LambdaMART Using Oblivious Trees
 Location: Room EF122, Engineering Building EF (Callaghan Campus) The University of Newcastle
 Time and Date: 2:00 pm, Fri, 28^{th} Oct 2016
 Note change of date.
 Abstract:
Learning to rank is a machine learning technique broadly used in many areas such as document retrieval, collaborative filtering or question answering. We present experimental results which suggest that the performance of the current stateoftheart learning to rank algorithm LambdaMART, when used for document retrieval for search engines, can be improved if standard regression trees are replaced by oblivious trees. This paper provides a comparison of both variants and our results demonstrate that the use of oblivious trees can improve the performance by more than 2:2%. Additional experimental analysis of the inuence of a number of features and of a size of the training set is also provided and confirms the desirability of properties of oblivious decision trees.
About the Speaker: Dr Michal Ferov is a Postdoctoral Research Fellow in the School of Mathematical and Physical Sciences,Faculty of Science and Information Technology.
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 CARMA GROUP THEORY RHD MEETING
 Speaker: Dr Michal Ferov, CARMA, The University of Newcastle
 Title: Separability properties and graph products of groups
 Location: Room V205, Mathematics Building (Callaghan Campus) The University of Newcastle
 Time and Date: 11:00 am, Thu, 20^{th} Oct 2016
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