ValueError: Could not find root within given tolerance. (80.1718646366842087309 > 2.16840434497100886801e-19)
Try another starting point or tweak arguments.
p_i = nsolve(mu * Constant.eta3Diff(k, f, p).subs(p, p_i) / (k - p_i1) * (p_i - p_i1) - dx,
p_i1, 1)