(*  Find the fixed points of the FitzHugh-Nagumo model *)

(*  First, write down the right hand sides of each equation.  Note that we need to label the parameter "I" as "J" because Mathematica defines I as the (Sqrt[-1]).  *)
f = V - ((V^3)/3)-W + J;
g = ϕ(V + a -b W);

(*  Then solve the system of two equations for the fixed points.  *)
fps = Solve[{f==0, g==0}, {V, W}]

(*  The horror!  There are 3 solutions.  Look at the first one.  *)
fp1 = fps[[1]];

(*  Plug in values for the parameters a, b, and phi.  *)
nfp1 = fp1/.{a->0.7, b->0.8, phi->0.08};

(*  Plot the fixed point in the voltage.  Note this does not reveal the stability of the fixed point.  *)
Plot[V/.nfp1, {J, 0,2}, AxesLabel->{"Input Current (I)", "Fixed Point in V"}]