Method getBasicVariablesInterface

highs/lp_data/HighsInterface.cpp:1438–1476

Get the basic variables, performing INVERT if necessary

// Get the basic variables, performing INVERT if necessary
HighsStatus Highs::getBasicVariablesInterface(HighsInt* basic_variables) {
  HighsStatus return_status = HighsStatus::kOk;
  HighsLp& lp = model_.lp_;
  HighsInt num_row = lp.num_row_;
  HighsInt num_col = lp.num_col_;
  HighsSimplexStatus& ekk_status = ekk_instance_.status_;
  // For an LP with no rows the solution is vacuous
  if (num_row == 0) return return_status;
  if (!basis_.valid) {
    highsLogUser(options_.log_options, HighsLogType::kError,
                 "getBasicVariables called without a HiGHS basis\n");
    return HighsStatus::kError;
  }
  if (!ekk_status.has_invert) {
    // The LP has no invert to use, so have to set one up, but only
    // for the current basis, so return_value is the rank deficiency.
    HighsLpSolverObject solver_object(lp, basis_, solution_, info_,
                                      ekk_instance_, callback_, options_,
                                      timer_);
    solver_object.setProfiling(this->profiling_);
    const bool only_from_known_basis = true;
    return_status = interpretCallStatus(
        options_.log_options,
        formSimplexLpBasisAndFactor(solver_object, only_from_known_basis),
        return_status, "formSimplexLpBasisAndFactor");
    if (return_status != HighsStatus::kOk) return return_status;
  }
  assert(ekk_status.has_invert);

  for (HighsInt row = 0; row < num_row; row++) {
    HighsInt var = ekk_instance_.basis_.basicIndex_[row];
    if (var < num_col) {
      basic_variables[row] = var;
    } else {
      basic_variables[row] = -(1 + var - num_col);
    }
  }
  return return_status;
}

// Solve (transposed) system involving the basis matrix