The Ramanujan Journal ( IF 0.7 ) Pub Date : 2020-07-23 , DOI: 10.1007/s11139-020-00279-6 K. Castillo , M. N. de Jesus , F. Marcellán , J. Petronilho
In this work we study orthogonal polynomials via polynomial mappings in the framework of the \(H_q\)-semiclassical class. We consider two monic orthogonal polynomial sequences \(\{p_n (x)\}_{n\ge 0}\) and \(\{q_n(x)\}_{n\ge 0}\) such that
$$\begin{aligned} p_{kn}(x)=q_n(x^k),\quad n=0,1,2,\ldots , \end{aligned}$$where \(k\ge 2\) is a fixed integer number, and we prove that if one of the sequences, \(\{p_n (x)\}_{n\ge 0}\) or \(\{q_n(x)\}_{n\ge 0}\), is \(H_q\)-semiclassical, then so is the other one. In particular, we show that if \(\{p_n(x)\}_{n\ge 0}\) is \(H_q\)-semiclassical of class \(s\le k-1\), then \(\{q_n (x)\}_{n\ge 0}\) is \(H_{q^k}\)-classical. This fact allows us to recover and extend recent results in the framework of cubic transformations (\(k=3\)). We also provide illustrative examples of \(H_{q}\)-semiclassical sequences of classes 1 and 2 involving little q-Laguerre and little q-Jacobi polynomials, including discrete measure representations for some of the considered examples.
中文翻译:
$$ H_q $$ H q-通过多项式映射的半经典正交多项式
在这项工作中,我们通过\(H_q \)-半经典类的框架中的多项式映射研究正交多项式。我们考虑两种首一正交多项式序列\(\ {P_N(X)\} _ {N \ GE 0} \)和\(\ {Q_N(X)\} _ {N \ GE 0} \) ,使得
$$ \ begin {aligned} p_ {kn}(x)= q_n(x ^ k),\ quad n = 0,1,2,\ ldots,\ end {aligned} $$其中\(k \ ge 2 \)是一个固定的整数,我们证明了如果其中一个序列是\(\ {p_n(x)\} _ {n \ ge 0} \)或\(\ {q_n (x)\} _ {n \ ge 0} \),是\(H_q \)-半经典的,那么另一个也是。特别地,我们证明如果\(\ {p_n(x)\} _ {n \ ge 0} \)是\(H_q \) -类\(s \ le k-1 \)的半经典,则\( \ {q_n(x)\} _ {n \ ge 0} \)是\(H_ {q ^ k} \)-经典。这个事实使我们能够在三次变换(\(k = 3 \))的框架内恢复和扩展最近的结果。我们还提供\(H_ {q} \)的说明性示例-涉及很少q -Laguerre和很少q -Jacobi多项式的类1和2的半经典序列,包括一些所考虑示例的离散测度表示。