Zh. Cao et Dj. Evans, A NOTE ON THE STRENGTHENED CAUCHY-BUNIAKOWSKII-SCHWARZ INEQUALITY OF A SYMMETRICAL SEMIDEFINITE MATRIX, International journal of computer mathematics, 47(3-4), 1993, pp. 231-237
In this paper the existence of a strengthened Cauchy-Buniakowskii-Schw
arz inequality is shown to be necessary and sufficient for a symmetric
and positive semi-definite matrix in the analysis of multi-level iter
ative methods.