ИСТИНА

Necessary optimality conditions in the form of the maximum principle for control problems with infinite time horizon are applied. With zero real interest rate the present value of firm profit, which is the objective functional, can be infinite and usually used transversality conditions can be inapplicable, even though maximum principle holds for the concept of overtaking or weakly overtaking optimality. New formula developed by S.M. Aseev and A.V. Kryazhimskiy for adjoint variable, that corresponds to a new form transversality condition, is implemented and its economic meaning is explained. The new condition completes the necessary conditions of maximum principle and extends its applicability to the cases where transversality conditions usually used in the literature do not hold, as demonstrated by the problem in hand. We also consider the canonical "q-theory" of investment under adjustment costs and zero interest rate.