My simple program demostrates how to apply Sharfetter-Gummel and Improved Sharfetter-Gummel procedure to calculate fluxes for convection-diffusion equation. It illustrate example and method from article by A. A. Kulikovsky "A More Accurate Sharfetter-Gummel Algorithm of Electron Transport for Semiconductor and Gas Discharge Simulation" // Journal of Computational Physics, 119, pp.149-155 (155).
Also Method of lines (MOL) for time-discretization and Finite Volume (FV) for spatial flux derivative have exploited.
Feel free to ask any questions.