J. Aust. Math. Soc.  76 (2004), 317-328
On decomposition of sub-linearised polynomials

Robert S. Coulter
  Department of Mathematical Sciences
  University of Delaware
  Newark, DE 19716-2553
  USA
  coulter@math.udel.edu
George Havas
  Centre for Discrete Mathematics
  and Computing
  School of Information Technology
  and Electrical Engineering
  The University of Queensland
  Qld 4072
  Australia
  havas@itee.uq.edu.au
and
Marie Henderson
  Department of Mathematical Sciences
  University of Delaware
  Newark, DE 19716-2553
  USA
  marie@math.udel.edu


Abstract
We give a detailed exposition of the theory of decompositions of linearised polynomials, using a well-known connection with skew-polynomial rings with zero derivative. It is known that there is a one-to-one correspondence between decompositions of linearised polynomials and sub-linearised polynomials. This correspondence leads to a formula for the number of indecomposable sub-linearised polynomials of given degree over a finite field. We also show how to extend existing factorisation algorithms over skew-polynomial rings to decompose sub-linearised polynomials without asymptotic cost.
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