Can anyone give some advice about books where I could find introductory information about Green's function. What are the methods of constructing Green's function. Actually, Green's function for 3D diffusion equation in unbounded domain is of interest. I am novice in this topic (Green's function for ODE and PDE) and any help is appreciated. Thank you in advance!
I think that "Boundary Value Problems and Green's Functions" by Stakgold and Holst is a good text.