In stochastic calculus, the Kunita–Watanabe inequality is a generalization of the Cauchy–Schwarz inequality to integrals of stochastic processes. It was first obtained by Hiroshi Kunita and Shinzo Watanabe and plays a fundamental role in their extension of Ito's stochastic integral to square-integrable martingales.[1]
Statement of the theorem
[edit]Let M, N be continuous local martingales and H, K measurable processes. Then
where the angled brackets indicates the quadratic variation and quadratic covariation operators. The integrals are understood in the Lebesgue–Stieltjes sense.
References
[edit]- Rogers, L. C. G.; Williams, D. (1987). Diffusions, Markov Processes and Martingales. Vol. II, Itô, Calculus. Cambridge University Press. p. 50. doi:10.1017/CBO9780511805141. ISBN 0-521-77593-0.