Aopt                    Calculate the A-optimal design under the
                        second-order Least squares estimator
Dopt                    Calculate the D-optimal design under the SLSE
calc_phi                Calculate the loss function of the A-, c- or
                        D-optimal design
copt                    Calculate the c-optimal design under the SLSE
                        with the given combination of the parameters
plot_dispersion         Verify the optimality condition for an optimal
                        design (A-, c- or D-optimality)
plot_weight             Plot the weight distribution of the optimal
                        design for univaraite regression model
