This solves the Bogoliubov-de Gennes equations and gap equations in the s-wave superconductor with the use of the Reduced-Shifted Conjugate-Gradient Method method. See, Y. Nagai, Y. Shinohara, Y. Futamura, and T. Sakurai,[arXiv:1607.03992v2 or DOI:10.7566/JPSJ.86.014708]. http:https://dx.doi.org/10.7566/JPSJ.86.014708

This code is for understanding the methods. This code ISNOT the fastest code.