Muthahharah, S. et al. 2026. Modeling The Open Unemployment Rate Using A Ridge-Fourier Series Estimator In Nonparametric Regression. KUBIK: Jurnal Publikasi Ilmiah Matematika. 10, 2 (Apr. 2026), 141–151. DOI:https://doi.org/10.15575/kubik.v10i2.55078.