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JOURNALS // Izvestiya Rossiiskoi Akademii Nauk. Seriya Matematicheskaya // Archive

Izv. Akad. Nauk SSSR Ser. Mat., 1972 Volume 36, Issue 4, Pages 789–794 (Mi im2334)

On interpolation theory in the complex domain

D. L. Berman


Abstract: It is shown that for the nodes $z_k^{(n)}=e^{i\theta_k^{(n)}}$, where $\theta_k^{(n)}=\frac{(2k+1)\pi}n$, $k=1,\dots,n$; $n=1,2,\dots$, the following statements hold: 1) The Hermite–Fejér interpolation process for an arbitrary polynomial converges in $|z|\leqslant1$ with rapidity $O\bigl(\frac1n\bigr)$. 2) The process $R_n(f,z)=\sum_{k=1}^nf\bigl(z_k^{(n)}\bigl)\bigl[l_k^{(n)}(z)\bigr]^2$, where $\bigl\{l_k^{(n)}(z)\bigr\}$ are Lagrange fundamental polynomials with nodes $\bigl\{z_k^{(n)}\bigr\}$, diverges at all points $z\ne0$ of $|z|\leqslant1$ for every function $f(z)=z^s$, $s=0,1,2,\dots$ .

UDC: 517.537

MSC: 30A80, 30A82

Received: 03.05.1971


 English version:
Mathematics of the USSR-Izvestiya, 1972, 6:4, 782–787

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© Steklov Math. Inst. of RAS, 2024