calculate_se_from_cov : Standard errors from covariance matrix
calculate_corr_from_cov : Correlation matrix from covariance matrix
calculate_cov_from_prec : Covariance matrix from precision matrix
calculate_cov_from_corrse : Covariance matrix from correlation matrix and standard errors
calculate_prec_from_cov : Precision matrix from covariance matrix
calculate_prec_from_corrse : Precision matrix from correlation matrix and standard errors
calculate_corr_from_prec : Correlation matrix from precision matrix