Timon @TSGut has done the heavy lifting and has implemented Jacobi matrices for Zernike polynomials on a disc. Alberto @APaganini could you remind us what exactly you required? If I remember correctly, as a first step you wanted to solve -Laplace(u)(x,y) = q(x,y) u(x,y) on a disc with zero Dirichlet bcs. What should we pick for q(x,y)? (@dlfivefifty)