As far as I know, the definition of fixed point you gave is wrong. The fixed point is defined as \frac{dx}{dt} = f(x*) = 0 (look at Nonlinear Dynamics and Chaos, Steven H. Strogatz) then the problem is to find x* satisfying: tanh(x*)= 0 .. Additionally, although, tanh(x*) = x* seems not to...