On the Kostlan--Shub--Smale model for random polynomial systems. Variance of the number of roots

  • Authors:
  • Mario Wschebor

  • Affiliations:
  • Centro de Matemática, Facultad de Ciencias, Universidad de la República, Calle Iguá 4225, 11400 Montevideo, Uruguay

  • Venue:
  • Journal of Complexity
  • Year:
  • 2005

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Abstract

We consider a random polynomial system with m equations and m real unknowns. Assume all equations have the same degree d and the law on the coefficients satisfies the Kostlan-Shub-Smale hypotheses. It is known that E(N^X)=d^m^/^2 where N^X denotes the number of roots of the system. Under the condition that d does not grow very fast, we prove that limsup"m"-"+"~VarN^Xd^m^/^2==3 then VarN^Xd^m^/^2-0 as m-+~, which implies N^Xd^m^/^2-1 in probability.