A semiclassical perspective on multivariate orthogonal polynomials
  Differential properties for orthogonal polynomials in several variables are studied. We consider multivariate orthogonal polynomials whose gradients satisfy some quasi--orthogonality conditions. We obtain several characterizations for these polynomials including the analogous of the semiclassical Pearson differential equation, the structure relation and a differential--difference equation. 
M. Alvarez de Morales, L. Fern\'andez, T. E. P\'erez, M. A. Pi\~nar