code: def getV0(self, v_mag_guess, buses, generators, type=CASE_GUESS):
          
          if type == CASE_GUESS:
              Va = array([b.v_angle * (pi / 180.0) for b in buses])
              Vm = array([b.v_magnitude for b in buses])
              V0 = Vm * exp(1j * Va)
          elif type == FLAT_START:
              V0 = ones(len(buses))
          elif type == FROM_INPUT:
              V0 = v_mag_guess
          else:
              raise ValueError
  
          # Set the voltages of PV buses and the reference bus in the guess.
  #        online = [g for g in self.case.generators if g.online]
          gbus = [g.bus._i for g in generators]
          Vg = array([g.v_magnitude for g in generators])
  
          V0[gbus] = Vg * abs(V0[gbus]) / V0[gbus]
  
          return V0
docs: Returns the initial voltage profile.