http://en.wikipedia.org/wiki/Nodal_analysis

http://www.ee.ic.ac.uk/hp/staff/dmb/courses/ccts1/03Nodal.pdf

http://en.wikipedia.org/wiki/Mesh_analysis

http://www.allaboutcircuits.com/vol_1/chpt_10/index.html

http://utwired.engr.utexas.edu/rgd1/lesson06.cfm