Green-function representation
= Green-function representation
If $G(x;\xi)$ satisfies the boundary conditions and $L_xG(x;\xi)=\delta(x-\xi)$, then a solution of $Ly=f$ is
$$
y(x)=\int G(x;\xi)f(\xi)\,d\xi,
$$
up to any homogeneous contribution required by nonhomogeneous boundary data.