Dear all, my question is addressed to the authors of https://github.com/scipy/scipy/blob/master/scipy/optimize/nonlin.py. I am looking for more detailed description of the nonlinear integro-differential equation which is a test problem for Newton-Krylov iteration in the documentation: \nabla^2 P = 10 \left(\int_0^1\int_0^1\cosh(P)\,dx\,dy\right)^2 As a computational scientist I would like to know the origin of this problem and possibly to get some references on related scientific papers. Thank you very much! Best, Boris