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Integral representation and embedding of weak Markov systems. (English) Zbl 0688.41038

R. Zielke [ibid. 44, 30-42 (1985; Zbl 0584.41013)] proved that a nondegenerate normalized weak Markov system is representable. In the present paper the author proves that the same property is valid for weakly nondegenerate normalized weak Markov systems. A system \(Z_ n=\{z_ 0,...,z_ n\}\) of real functions defined on a set \(A\subset {\mathbb{R}}\) is called weakly nondegenerate provided that the following condition is satisfied: If \(Z_ n\) is linearly independent on \([c<\infty)\cap A\), where c is an arbitrary point in the convex hull of A, then there exists a set \(U_ n\), obtained from \(Z_ n\) by a triangular linear transformation, such that for any sequence \(\{\) k(r); \(r=0,...,m\}\) with k(0)\(\geq 0\) and k(m)\(\leq n\) that is either strictly increasing or constant, the set \(\{u_{k(r)}\); \(r=0,...,m\}\) is a weak Markov system on [c,\(\infty)\cap A\); a similar condition is supposed if \(Z_ n\) is linearly independent on (-\(\infty,c]\cap A\). (Naturally one suppose that \(Z_ n\) is linearly independent on at least one of the sets [c,\(\infty)\cap A\) and (-\(\infty,c]\cap A\) for every real number c. Markov system \(=\) complete Chebyshev system.)
Reviewer: B.Crstici

MSC:

41A65 Abstract approximation theory (approximation in normed linear spaces and other abstract spaces)
41A50 Best approximation, Chebyshev systems
26A51 Convexity of real functions in one variable, generalizations

Citations:

Zbl 0584.41013
Full Text: DOI

References:

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