http://quantlib.414.s1.nabble.com/boundary-condition-question-tp6831p6833.html
In the last while I have been working with another approach (my basic standpoint now is that truncation of the boundary and the impositions of ad-hoc BC on new boundaries is *not* the way to go).
New method involves mapping semi-infinite interval (0, INFINITY) to (0,1) (e..g. y = exp(cx), tahn(cx) etc.) and using Fichera theory. The maths is correct and very clear.
The idea is not new.
Numerics: I am getting excellent results.
Maybe this helps
Daniel
// slide show on Fichera BC
// You need to install Texpoint to view the maths formulae