code: def _get_voltage_magnitude_var(self, buses, generators):
          
          Vm = array([b.v_magnitude for b in buses])
  
          # For buses with generators initialise Vm from gen data.
          for g in generators:
              Vm[g.bus._i] = g.v_magnitude
  
          Vmin = array([b.v_min for b in buses])
          Vmax = array([b.v_max for b in buses])
  
          return Variable("Vm", len(buses), Vm, Vmin, Vmax)
docs: Returns the voltage magnitude variable set.