Siregar, Naufal Ramadhan Al Akhwal, dkk. “Pemodelan Harga Minyak Mentah Dunia Berdasarkan Efek Pandemi Covid-19 Dengan Estimator Penalized Spline”. MUST: Journal of Mathematics Education, Science and Technology, vol. 7, no. 2, Desember 2022, hlm. 152-66, doi:10.30651/must.v7i2.16377.