Mon Oct 27 11:20:20 EDT 2014

Spice DC analysis, voltages sources and Thevenin equivalent circuit

In [1] it is mentioned that

- Current sources and resistors mix very well as they give simple
  linear systems in terms of node voltages when Kirchhoff's Current Law
  (KCL) is used for every node.

- The presence of a voltage source messes up this pretty picture.  See
  page 10 in [1].

I vaguely remember running into this in class, but thinking about it,
the statement "we cannot form the matrix equations" seems a bit hard
to believe.  What exactly is the limitation?  Surely there are 3
linear equations in 3 unknowns (I1, V2, V2) in Figure 2.

I guess the point is here that when all voltage sources are replaced
with current sources, the problem is a lot easier to state since all
node voltages are variables and for each node there is a KCL equation.
No need to keep track of which voltages are variables and which are

[1] http://www3.imperial.ac.uk/pls/portallive/docs/1/7292571.PDF