Use differntial evolution method to search for a positive definite matrix.
AlterMatrixUsingDE(V.modified)a matrix
a postive definite matrix.
The function is developed based on the theoretical method in Misha (2007), we apply it to search the positive definite matrix. It first starts search with the element in upper triangular matrix of the variance covariance matrix, then tries to search the positive definite matrix with all nonnegative elements.
Mishra, S.K. 2007. The nearest correlation matrix problem: Solution by differential evolution method of global optimization. dx.doi.org/10.2139/ssrn.980403.