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Dr Cian O'Brien

Dr Cian O'Brien


School of Mathematics

+44 29208 74813
1.09, Abacws, Senghennydd Road, Cathays, Cardiff, CF24 4AG


My research is focused on alternating sign matrices and their relationships to graph theory, linear algebra, design theory, and group theory.

This semester, I am the lecturer for Linear Algebra II. I have previous teaching experience in linear algebra, group theory, combinatorics, rings and fields, and Python programming.


  • 2020 - 2021: Postdoctoral Researcher, NUI Galway, Ireland
  • 2019 - 2020: Lecturer, NUI Galway, Ireland
  • 2016 - 2020: PhD, NUI Galway, Ireland




Autumn Semester 21/22

  • Linear Algebra II

Past Teaching Experience

  • Group Theory
  • Linear Algebra
  • Programming for Science and Finance
  • Discrete Mathematics
  • Algebraic Structures


Broadly speaking, my research interests lie within the areas of combinatorial matrix theory, graph theory, and design theory. My main objects of study are alternating sign matrices, which are (0,1,-1)-matrices in which the non-zero entries of each row and column alternate in sign, beginning and ending with 1.

Particular objects of interest to me include alternating signed bipartite graphs and related edge colouring problems, alternating sign hypermatrices and related Latin-like square structures, and finite subgroups of GL(n,Q) generated by alternating sign matrices.

Research Group

Geometry, Algebra, Mathematical Physics and Topology

Conference Talks