On series of orthogonal polynomials and systems of classical type polynomials

UDC 517.587 If $\displaystyle\sum\nolimits_{k=0}^\infty c_k g_k(x),$ is a formal series of orthonormal polynomials $g_k(x)$ on the real line that has positive coefficients $c_k,$ then its partial sums $u_n(x)$ are associated with Jacobi type pencils.Therefore, they possess a recurrence relation and...

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Datum:2021
Hauptverfasser: Zagorodnyuk, S. M., Zagorodnyuk, Sergey, Загороднюк , С. М.
Format: Artikel
Sprache:Ukrainisch
Veröffentlicht: Institute of Mathematics, NAS of Ukraine 2021
Online Zugang:https://umj.imath.kiev.ua/index.php/umj/article/view/6527
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Назва журналу:Ukrains’kyi Matematychnyi Zhurnal
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Ukrains’kyi Matematychnyi Zhurnal
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Zusammenfassung:UDC 517.587 If $\displaystyle\sum\nolimits_{k=0}^\infty c_k g_k(x),$ is a formal series of orthonormal polynomials $g_k(x)$ on the real line that has positive coefficients $c_k,$ then its partial sums $u_n(x)$ are associated with Jacobi type pencils.Therefore, they possess a recurrence relation and special orthonormality conditions.The cases where $g_k(x)$ are Jacobi or Laguerre polynomials will be of a special interest.For a suitable choice of parameters~$c_k,$ the partial sums $u_n(x)$ are Sobolev orthogonal polynomials with a $(3\times 3)$ matrix measure.A~further selection of parameters gives differential equations for $u_n.$In this case, polynomials $u_n(x)$ are solutions to generalized eigenvalue problems both in $x$ and in $n.$
DOI:10.37863/umzh.v73i6.6527