M. G. Dmitriev, Yu. A. Konyaev, “The Birgchof type asymptotics of some singularly perturbed optimal control problems”, Matem. Mod., 14:3 (2002), 27–29
For one class of linear-quadratic optimal control problems (in case when it is not possible to use boundary functions method) it the variant of Birgchof–Tamarkin–Lomov method is offered. This method lets to construct the quasi-regular asymptotics of the singular solution, which may be written in closed analytical form.