Given the PDE: $$ \nabla \cdot [\sigma(x,y,z)\nabla\phi]=-\frac{\partial \rho}{\partial t} \delta(x_s)\delta(y_s)\delta(z_s) $$
The RHS is the source term, which is represented by a 3D delta function. If there are two source terms, can I solve for $\phi$ for each source and then apply linear superposition to obtain the final solution?