Functional decomposition of polynomials: The wild case

  • Authors:
  • Joachim von zur Gathen

  • Affiliations:
  • Department of Computer Science, University of Toronto Toronto, Ontario M5S 1A4, Canada

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 1990

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Abstract

If g and h are polynomials of degrees r and s over a field, their functional composition f = g(h) has degree n = rs. The functional decomposition problem is: given f of degree n = rs, determine whether such g and h exist, and, in the affirmative case, compute them. An apparently difficult case is when the characteristic p of the ground field divides r. This paper presents a polynomial-time partial solution for this ''wild'' case; it works, e.g., when p^2 @? r.