The C++ function hess_HMM_stat_dir_oe_re_K1() updates the Hessian matrix when the number of cluster is 1 in a static binary directed network. (The above description may need further improvement.)
hess_HMM_stat_dir_oe_re_K1(theta, N)
Vector of current theta
(network canonical parameters) values.
Number of nodes.
Returns the Hessian matrix of ELBO with respect to theta parameters for Newton-Raphson update in M-step.