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The field of Nash functions and factorization of polynomials

Stanisław Spodzieja — 1996

Annales Polonici Mathematici

The algebraically closed field of Nash functions is introduced. It is shown that this field is an algebraic closure of the field of rational functions in several variables. We give conditions for the irreducibility of polynomials with Nash coefficients, a description of factors of a polynomial over the field of Nash functions and a theorem on continuity of factors.

The Łojasiewicz exponent of subanalytic sets

Stanisław Spodzieja — 2005

Annales Polonici Mathematici

We prove that the infimum of the regular separation exponents of two subanalytic sets at a point is a rational number, and it is also a regular separation exponent of these sets. Moreover, we consider the problem of attainment of this exponent on analytic curves.

Sum of squares and the Łojasiewicz exponent at infinity

Krzysztof KurdykaBeata Osińska-UlrychGrzegorz SkalskiStanisław Spodzieja — 2014

Annales Polonici Mathematici

Let V ⊂ ℝⁿ, n ≥ 2, be an unbounded algebraic set defined by a system of polynomial equations h ( x ) = = h r ( x ) = 0 and let f: ℝⁿ→ ℝ be a polynomial. It is known that if f is positive on V then f | V extends to a positive polynomial on the ambient space ℝⁿ, provided V is a variety. We give a constructive proof of this fact for an arbitrary algebraic set V. Precisely, if f is positive on V then there exists a polynomial h ( x ) = i = 1 r h ² i ( x ) σ i ( x ) , where σ i are sums of squares of polynomials of degree at most p, such that f(x) + h(x) > 0 for x...

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