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This article is cited in 6 scientific papers (total in 6 papers)
Exact bounds for simultaneous approximation of functions of two variables and their derivatives by bilinear splines
M. Sh. Shabozov Tajik State University
Abstract:
We find the exact value of the expression
\begin{multline}\quad
\varepsilon^{(l,q)}\bigl(W^{(r,s)}H^{\omega_1,\omega_2}(G)\bigr)=\sup\bigl\{\|f^{(l,q)}(\cdot,\cdot) -S_{1,1}^{(l,q)}(f;\cdot,\cdot)\|_{C(G)}: f\in W^{(r,s)}H^{\omega_1,\omega_2}(G)\bigr\},
\end{multline}
where $\varphi^{(l,q)}(x,y)=\partial^{1+q}\varphi/\partial x^l\partial y^q$
($l,q=0,1$, $1\le l+q\le2$) and $S_{1,1}(f;x,y)$ is a bilinear spline interpolating $f(x,y)$ in the nodes of the grid $\Delta_{mn}=\Delta_m^x\times\Delta_n^y$ with $\Delta_m^x$: $x_i=i/m$ ($i=\overline{0,m}$), $\Delta_n^y$: $y_j=j/n$ ($j=\overline{0,n}$). Here $W^{(r,s)}H^{\omega_1,\omega_2}(G)$ is the class of functions $f(x,y)$ with continuous derivatives $f^{(r,s)}(x,y)$ ($r,s=0,1$, $1\le r+s\le2$) on the square $G=[0,1]\times[0,1]$ and with the modulus of continuity satisfying the inequality ($\omega(f^{(r,s)};t,\tau)\le\omega_1(t)+\omega_2(\tau)$, where $\omega_1(t)$ and $\omega_2(t)$ are the given moduli of continuity.
Received: 07.10.1994
Citation:
M. Sh. Shabozov, “Exact bounds for simultaneous approximation of functions of two variables and their derivatives by bilinear splines”, Mat. Zametki, 59:1 (1996), 142–152; Math. Notes, 59:1 (1996), 104–111
Linking options:
https://www.mathnet.ru/eng/mzm1701https://doi.org/10.4213/mzm1701 https://www.mathnet.ru/eng/mzm/v59/i1/p142
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