
A classical result of Laguerre and Pólya asserts that a real entire function \(f\) can be uniformly approximated on bounded subsets of \(\mathbb C\) by polynomials having only real zeros if and only if f(z) can be expressed in the form \[ f(z)=c z^m e^{\alpha z-\gamma z^2}\prod_{k=1}^\omega \left(1+ \frac z{x_k}\right)e^{-\frac z{x_k}}, \qquad (1\leq \omega \leq \infty), \] where \(c,\alpha, x_k \in \mathbb R\), \(c, x_k \neq 0\), \(\gamma \geq 0\), \(m\) is a nonnegative integer and \(\sum_{k=1}^\infty 1/x_k^2 < \infty\). The purpose of the paper under review is to generalize this theorem. Let \(B\) be a finite set of positive integers and let \(\Theta\) denote a set of real numbers which is unbounded on both sides. The author characterizes the entire functions that can be uniformly approximated on bounded sets by polynomials of the form \(p(z)=\prod_{j \in B}p_j(z^j)\), where \(p_j(z)\) is a polynomial all of whose zeros lie in \(\Theta\).
Mathematics(all), Numerical Analysis, approximations, Representations of entire functions of one complex variable by series and integrals, Zeros of polynomials, rational functions, and other analytic functions of one complex variable (e.g., zeros of functions with bounded Dirichlet integral), Polynomials and rational functions of one complex variable, Applied Mathematics, Special classes of entire functions of one complex variable and growth estimates, Laguerre-Pólya class, Analysis, entire functions
Mathematics(all), Numerical Analysis, approximations, Representations of entire functions of one complex variable by series and integrals, Zeros of polynomials, rational functions, and other analytic functions of one complex variable (e.g., zeros of functions with bounded Dirichlet integral), Polynomials and rational functions of one complex variable, Applied Mathematics, Special classes of entire functions of one complex variable and growth estimates, Laguerre-Pólya class, Analysis, entire functions
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