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arXiv math/0603366math.CA
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导数也正交的矩阵正交多项式

Matrix orthogonal polynomials whose derivatives are also orthogonal

M. J. Cantero, L. Moral, L. Velazquez

摘要:

本文证明了导数也正交的矩阵正交多项式的一些特征,推广了标量情形下已知的一些特征。特别地,我们证明了相应的正交矩阵泛函的特征在于一个皮尔逊型方程的两个矩阵多项式的次数不大于大于2和1。给出了一般矩阵正交多项式序列的证明,不一定与厄米特泛函有关。然而,我们给出了几个例子,不可对角化正定重量矩阵满足皮尔逊型方程,这表明以前的结果是非平凡的,即使在正定的情况下。本文对满足皮尔逊型方程的一类矩阵泛函作了详细的分析,该方程的多项式的次数不大于大于2是标量的。我们刻画了这类Pearson型方程的特征,得到了一系列矩阵正交多项式,并证明了这些矩阵正交多项式即使在非厄米特情形下也满足一个二阶微分方程.最后,我们证明并改进了Duran和Grunbaum关于这类泛函在正定情形下平凡性的一个猜想,同时通过一些例子证明了非正定的Hermite泛函的非平凡性.

英文摘要:

In this paper we prove some characterizations of the matrix orthogonal polynomials whose derivatives are also orthogonal, which generalize other known ones in the scalar case. In particular, we prove that the corresponding orthogonality matrix functional is characterized by a Pearson-type equation with two matrix polynomials of degree not greater than 2 and 1. The proofs are given for a general sequence of matrix orthogonal polynomials, not necessarily associated with an hermitian functional. However, we give several examples of non-diagonalizable positive definite weight matrices satisfying a Pearson-type equation, which show that the previous results are non-trivial even in the positive definite case. A detailed analysis is made for the class of matrix functionals which satisfy a Pearson-type equation whose polynomial of degree not greater than 2 is scalar. We characterize the Pearson-type equations of this kind that yield a sequence of matrix orthogonal polynomials, and we prove that these matrix orthogonal polynomials satisfy a second order differential equation even in the non-hermitian case. Finally, we prove and improve a conjecture of Duran and Grunbaum concerning the triviality of this class in the positive definite case, while some examples show the non-triviality for hermitian functionals which are not positive definite.

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