Richard S. Varga, Hermite interpolation-type Ritz methods for two-point boundary value problems, Numerical Solution of Partial differential Equations (J. H. Bramble, ed. ), pp. 365-373, Academic Press, Inc., New York, 1966. MR 34, 5302. Zbl. 161, p. 357.
In the important work of Bramble and Hubbard , higher-order difference approximations of order O(h4) are used at interior mesh points for two-point self-adjoint second-order boundary value problems, while lower-order difference approximations are used near the boundary points. The resulting matrix equations are such that the associated matrices A are nonsymmetric, but possess the attractive property that A-1 > 0. Moreover, it is shown that the discretion error is also O(h4).