1. http://ngspice.sourceforge.net/docs/ngspice-manual.pdf
2. https://ecee.colorado.edu/~mathys/ecen1400/pdf/scad3.pdf
3. https://www.seas.upenn.edu/~jan/spice/PSpice_UserguideOrCAD.pdf
4. https://cseweb.ucsd.edu/classes/wi10/cse241a/assign/hspice_sa.pdf
5. https://ece.northeastern.edu/courses/eece7353/2019sp/hspice_sa.pdf