| A_x_B | A Kronecker product B | 
| check_periodicity | Checking the periodicity of parameters in the regression model | 
| DELTA | Calculating the component of vector DELTA | 
| estimate_para_adaptive_method | Adaptive estimator for periodic coefficients regression model | 
| GAMMA | Calculating the component of matrix GAMMA | 
| lm_per | Fitting periodic coefficients regression model by using LSE | 
| lm_per_AE | Fitting periodic coefficients regression model by using Adaptive estimation method | 
| LSE_Reg_per | Least squares estimator for periodic coefficients regression model | 
| phi_n | Calculating the value of phi function | 
| pseudo_gaussian_test | Detecting periodicity of parameters in the regression model | 
| sd_estimation_for_each_s | Estimating periodic variances in a periodic coefficients regression model |