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A tool for locating zeros of orthogonal polynomials in Sobolev inner product spaces. (English) Zbl 0792.42010

Summary: In the theory of polynomials orthogonal with respect to an inner product of the form \[ \langle f,g\rangle= \int^ \infty_ 0 f(x)g(x)d\psi(x)+ \sum^ m_{k=1} A_ k f^{(i_ k)}(0) g^{(i_ k)}(0), \] one is confronted with the following situation: for certain values of the parameters, the orthogonal polynomials of degree \(n\) does not have all its zeros inside the support of the distribution function \(d\psi\). This paper gives a method to investigate the zero distribution by looking at a type of limiting polynomial. For the case \(m=2\) it is shown that there are exactly two zeros outside the true interval of orthogonality for \(A_ 1\), \(A_ 2\) large; moreover, it is proved that these zeros are nonreal (complex conjugates) in the case \(i_ 1+ 1= i_ 2\). Also several examples are given.

MSC:

42C05 Orthogonal functions and polynomials, general theory of nontrigonometric harmonic analysis
Full Text: DOI

References:

[1] Marcellán, F.; Alfaro, M.; Rezola, M. L., Orthogonal polynomials on Sobolev spaces: old and new directions, J. Comput. Appl. Math., 48, 1-2, 113-131 (1993) · Zbl 0790.42015
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[4] Pólya, G.; Szegő, G., Problems and Theorems in Analysis II (1976), Springer: Springer New York · Zbl 0311.00002
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