V. Ratnasari, I. N. Budiantara, and A. T. R. Dani, “Nonparametric Regression Mixed Estimators of Truncated Spline and Gaussian Kernel based on Cross-Validation (CV), Generalized Cross-Validation (GCV), and Unbiased Risk (UBR) Methods”, Int. J. Adv. Sci. Eng. Inf. Technol., vol. 11, no. 6, pp. 2400–2406, Dec. 2021.