1D Green's function for the Laplacian

What you are seeing: the Green's function $G(x, x_0)$ for $-u'' = f$ on $[0, L]$ with Dirichlet boundary conditions. Drag the source location $x_0$; the Green's function (orange tent) is plotted. Below, the solution $u(x)$ for the user-selected $f(x)$, obtained via convolution with $G$.