code: def write_branch_data(self, file):
          
          branch_attr = ["r", "x", "b", "rate_a", "rate_b", "rate_c",
              "ratio", "phase_shift", "online", "ang_min", "ang_max", "p_from",
              "q_from", "p_to", "q_to", "mu_s_from", "mu_s_to", "mu_angmin",
              "mu_angmax"]
  
          file.write("\n%%%% branch data\n")
          file.write("%%\tfbus\ttbus\tr\tx\tb\trateA\trateB\trateC\tratio"
                     "\tangle\tstatus")
          file.write("\tangmin\tangmax")
          file.write("\tPf\tQf\tPt\tQt")
          file.write("\tmu_Sf\tmu_St")
          file.write("\tmu_angmin\tmu_angmax")
          file.write("\n%sbranch = [\n" % self._prefix)
  
          for branch in self.case.branches:
              vals = [getattr(branch, a) for a in branch_attr]
  
              vals.insert(0, branch.to_bus._i)
              vals.insert(0, branch.from_bus._i)
  
              file.write("\t%d\t%d\t%g\t%g\t%g\t%g\t%g\t%g\t%g\t%g\t%d\t%g\t%g"
                         "\t%.4f\t%.4f\t%.4f\t%.4f\t%.4f\t%.4f\t%.4f\t%.4f;\n" %
                         tuple(vals))
          file.write("];\n")
docs: Writes branch data to file.