A new modified Cholesky factorization
SIAM Journal on Scientific and Statistical Computing
Modified Cholesky factorizations for sparse preconditioners
SIAM Journal on Scientific Computing
Generating daily changes in market variables using a multivariate mixture of normal distributions
Proceedings of the 33nd conference on Winter simulation
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Mixture of normals is a more general and flexible distribution for modeling of daily changes in market variables with fat tails and skewness. An efficient analytical Monte Carlo method was proposed by Wang and Taaffe for generating daily changes using a multivariate mixture of normal distributions with arbitrary covariance matrix. However the usual Cholesky Decomposition will fail if the covariance matrix is not positive definite. In practice, the covariance matrix is unknown and has to be estimated. The estimated covariance may be not positive definite. We propose a modified Cholesky decomposition for semi-definite matrices and also suggest an optimal semi-definite approximation for indefinite matrices.