only if A is nonsingular, you can solve L(u)=f only if the problem is well-posed.) For example, suppose we want to solve the differential equation u"+x^3*u = 1 on the interval [-3,3] with Dirichlet boundary conditions. Here is a Chebfun solution: L = chebop(-3,3);L.op = @(x,u) diff(u,2) +