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Given a strongly regular Hankel matrix, and its associated sequence of moments whichdefines a quasi-definite moment linear functional, we study the perturbation of a fixedmoment, i.e., a perturbation of one antidiagonal of the Hankel matrix. We define a linearfunctional whose action results in such a perturbation and establish necessary and sufficientconditions in order to preserve the quasi-definite character. A relation between thecorresponding sequences of orthogonal polynomials is obtained, as well as the asymptoticbehavior of their zeros. We also study the invariance of the Laguerre-Hahn class of linearfunctionals under such perturbation, and determine its relation with the so-called canonicallinear spectral transformations.
hankel matrix; linear moment functional; orthogonal polynomials; laguerre-hahn class; zeros