Dear Sir/Madam，
Hello, I am interested in Green Function, so I read related Kwant codes (kwant.solver.greens_function, make_linear_system, solve_linear_system, etc.). I found a lot of optimizations in Kwant, such as LU Decomposition and Matrix Partition, which make Kwant more efficient. To calculate Green Function, we need to calculate the self-energy of leads. Though I know how to get self-energy by using command "lead.selfenergy(energy)". I want to know how this command works, the codes in "leads.py" are too diffcult to me. Sincerely, Hu Yongliang
