Pingak RK, Kolmate R, Bernandus B. A Simple Matrix Approach to Determination of the Helium Atom Energies. J. Penelit. Fis. Apl. [Internet]. 2019 Jun. 30 [cited 2025 Jun. 30];9(1):10-21. Available from: https://journal.unesa.ac.id/index.php/jpfa/article/view/2711