Before revision:  It is often of considerable interest to obtain numerical solutions for such equations, but the singular (" point-like " ) modeling of the sources in these problems typically introduces nontrivial obstacles for devising a satisfactory numerical implementation .
After revision:  It is often of considerable interest to obtain numerical solutions for such equations, but the singular (" particle " ) modeling of the sources in these problems typically introduces nontrivial obstacles for devising a satisfactory numerical implementation .