Build the log-likelihood function of the P-dynamics from the JLL-based models
llk_JLL_Sigma(VecPara, res, IdxNONzero, K)
value of the log-likelihood function (scalar)
vector that contains all the non-zero entries of the lower-triangular part of the Cholesky factorization
residuals from the VAR of the JLL model (K x T)
vector that contains indexes of the matrix of the non-zero entries of the Cholesky factorization
dimensions of the variance-covariance matrix (scalar)