RT Journal Article SR Electronic T1 On the Covariance Matrices Used in Value at Risk Models JF The Journal of Derivatives FD Institutional Investor Journals SP 50 OP 62 DO 10.3905/jod.1997.407974 VO 4 IS 3 A1 C.O. Alexander A1 C.T. Leigh YR 1997 UL https://pm-research.com/content/4/3/50.abstract AB