RT Journal Article T1 Structure theorems for linear and non-linear differential operators admitting invariant polynomial subspaces A1 Gómez-Ullate Otaiza, David A1 Kamran, Niky A1 Milson, Robert AB In this paper we derive structure theorems which characterize the spaces of linear and non-linear differential operators that preserve finite dimensional subspaces generated by polynomials in one or several variables. By means of the useful concept of deficiency, we can write an explicit basis for these spaces of differential operators. In the case of linear operators, these results apply to the theory of quasi-exact solvability in quantum mechanics, especially in the multivariate case where the Lie algebraic approach is harder to apply. In the case of non-linear operators, the structure theorems in this paper can be applied to the method of finding special solutions of non-linear evolution equations by nonlinear separation of variables. PB American Institute of Mathematical Sciences SN 1078-0947 YR 2007 FD 2007-05 LK https://hdl.handle.net/20.500.14352/51451 UL https://hdl.handle.net/20.500.14352/51451 LA eng NO © American Institute of Mathematical Sciences. DS Docta Complutense RD 25 abr 2025