A                       Calculation of the matrix A based on single
                        dataset
Sigma_cal               Variance-covariance matrix of the estimation
                        equation
est_ini                 Initial estimation
link_Hessian            Hessians of the link function
link_grad               gradient of the link function
mean_psi                Sample expectation of psi
mean_psi_pop            Sample expectation of POP-Inf psi
optim_est               Gradient descent for obtaining estimator
optim_weights           Gradient descent for obtaining the weight
                        vector
pop_M                   POP-Inf M-Estimation
psi                     Esimating equation
sim_data                Simulate the data for testing the functions
