On the Computational Complexity of Bongartz's Algorithm

  • Authors:
  • Andrzej Mróz

  • Affiliations:
  • Faculty of Mathematics and Computer Science, Nicolaus Copernicus University, Chopina 12/18, 87-100 Toruń, Poland. amroz@mat.umk.pl

  • Venue:
  • Fundamenta Informaticae
  • Year:
  • 2013

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Abstract

We study the complexity of Bongartz's algorithm for determining a maximal common direct summand of a pair of modules M, N over k-algebra Λ; in particular, we estimate its pessimistic computational complexity Orm6n2n + m log n, where m = dimkM ≤ n = dimkN and r is a number of common indecomposable direct summands of M and N. We improve the algorithm to another one of complexity Orm4n2n+m log m and we show that it applies to the isomorphism problem having at least an exponential complexity in a direct approach. Moreover, we discuss a performance of both algorithms in practice and show that the “average” complexity is much lower, especially for the improved one which becomes a part of QPA package for GAP computer algebra system.