Approximation of eigenvalues of nonselfadjoint problems on an infinite interval

The author treats the problem of approximation of the eigenvalues of the nonselfadjoint problem Lu=λu, u(0)=0, u∈L2(0,∞), where L=−d2/dt2+p(x), domL={u∈L2(0,∞):du/dt continuous, d2u/dt2∈L2(0,∞), u(0)=0}. The same question for a selfadjoint problem was answered in the author's recent paper.