
doi: 10.1137/0508022
The subject of this paper is to find an \(n\)-th degree polynomial which maximizes \[ R(f)=\int_{I_a}|f(x)|^2dx/\int_{I_b}|f(x)|^2dx \] where \(f\) is a complex valued function and \(I_a\), \(I_b\) are real intervals. Special attention is paid to the asymptotic behaviour of this maximum for \(n\to \infty\) for the so-called interior problem \((I_a\subset I_b)\) and the adjacent exterior problem (\(I_a \cap I_b =\mathrm{right endpoint of}\, I_b = \mathrm{left endpoint of}\, I_a\)); the formulae given are rather intricate. The problem at hand is equivalent to finding the largest eigenvalue of a matrix eigenvalue problem of the type \(Ax=\lambda Bx\) with \(A,B\) real symmetric positive definite \((n+ 1) \times (n + 1)\) matrices. The solution of this problem leads to \((n + 1)\) real eigenvalues \(\lambda_0^{(n)}\geq \lambda_1^{(n)} \geq \ldots \geq \lambda_n^{(n)}>0\) (of which \(\lambda_o^{(n)}\) is the maximum value of \(R(f)\) sought for) with real eigenvectors \(f_0^{(n)},\ldots ,f_n^{(n)}\) satisfying the double orthogonality property \[ (f_j^{(n)})^tBf_k^{(n)}=\delta_{jk},\, (f_j^{(n)})^tAf_k^{(n)}=\lambda_j^{(n)}\delta_j^{(n)}\, (j,k=0,1,\ldots ,n). \] Also the maximum problem is considered for two other kinds of concentrations, leading solutions using Tchebycheff polynomials (from \(|f(y)|^2/ \max \; |f(x)|^2;\;y\in I_a,\; S\subset I_b\)) and Legendre polynomials (from \(|f(y)|^2/\int_S|f(x)|^2dx;\; y\in I_a,\; S\in I_b\)). Furthermore an equivalent differential equation eigenvalue problem is derived in the case of the centered interior problem \((I_a=[-a,a]\), \(I_b=[-1,1];\; 01)\) including an asymptotic investigation for \(n\to \infty\) of these equations. Finally it must be said that the style of the paper is in tune with its title, very concentrated.
Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.), Computation of special functions and constants, construction of tables, Extremal problems for conformal and quasiconformal mappings, other methods
Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.), Computation of special functions and constants, construction of tables, Extremal problems for conformal and quasiconformal mappings, other methods
| selected citations These citations are derived from selected sources. This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | 14 | |
| popularity This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network. | Top 10% | |
| influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Top 1% | |
| impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |
