In this paper, we show that for several second-order partial differential equations \begin{align*}L[u] &= A(x,y)u_{xx} + 2B(x,y)u_{xy} + C(x,y)u_{yy} + D(x,y)u_x + E ...

Variable selection in multiple regression requires identifying the best subset from among a set of candidate predictors. In the case of polynomial regression, the variable selection process can be ...