MISolver.cc

/*===========================================================================*\
 *                                                                           *
 *                               CoMISo                                      *
 *      Copyright (C) 2008-2009 by Computer Graphics Group, RWTH Aachen      *
 *                           www.rwth-graphics.de                            *
 *                                                                           *
 *---------------------------------------------------------------------------*
 *  This file is part of CoMISo.                                             *
 *                                                                           *
 *  CoMISo is free software: you can redistribute it and/or modify           *
 *  it under the terms of the GNU General Public License as published by     *
 *  the Free Software Foundation, either version 3 of the License, or        *
 *  (at your option) any later version.                                      *
 *                                                                           *
 *  CoMISo is distributed in the hope that it will be useful,                *
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of           *
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the            *
 *  GNU General Public License for more details.                             *
 *                                                                           *
 *  You should have received a copy of the GNU General Public License        *
 *  along with CoMISo.  If not, see <http://www.gnu.org/licenses/>.          *
 *                                                                           *
\*===========================================================================*/

#include <CoMISo/Config/config.hh>
#include "MISolver.hh"
#include "CoMISo/Utils/CoMISoError.hh"

#if (COMISO_QT_AVAILABLE)
#include <CoMISo/QtWidgets/MISolverDialogUI.hh>
#endif

#if COMISO_CPLEX_AVAILABLE
#include <ilcplex/ilocplex.h>
ILOSTLBEGIN
#endif

#if COMISO_GUROBI_AVAILABLE
#include <gurobi_c++.h>
#endif

#define COMISO_MISOLVER_PERFORMANCE_TEST
#ifdef COMISO_MISOLVER_PERFORMANCE_TEST
#include "SparseQRSolver.hh"
#include "UMFPACKSolver.hh"
#include "EigenLDLTSolver.hh"
#endif

#include <CoMISo/Utils/gmm.hh>

#include <Base/Debug/DebTime.hh>
#include <Base/Utils/StopWatch.hh>

#include <queue>
#include <float.h>

#define ROUND(x) ((x) < 0 ? int((x) - 0.5) : int((x) + 0.5))

namespace COMISO
{
namespace
{

class RoundingQueue : protected std::priority_queue<std::pair<double, int>>
{
public:
  RoundingQueue(const double _threshold) : threshold_(_threshold), cur_sum_(0.0)
  {
    c.reserve(128);
  }

  void clear()
  {
    c.clear();
    cur_sum_ = 0.0;
  }

  void add(const int _id, const double _rd_val)
  {
    if (empty() || cur_sum_ + _rd_val <= threshold_)
    { // empty? -> always add one element
      emplace(_rd_val, _id);
      cur_sum_ += _rd_val;
      return;
    }
    if (top().first > _rd_val) // replace the last element if worse
    {
      cur_sum_ -= top().first;
      pop();
      emplace(_rd_val, _id);
      cur_sum_ += _rd_val;
    }
  }

  void get_ids(std::vector<int>& _ids)
  {
    _ids.clear();
    _ids.reserve(size());
    std::sort_heap(c.begin(), c.end());
    for (auto s_it = c.begin(); s_it != c.end(); ++s_it)
      _ids.push_back(s_it->second);
  }

private:
  const double threshold_;
  double cur_sum_;
};

// gmm Column and ColumnIterator of CSC matrix
typedef gmm::linalg_traits<MISolver::CSCMatrix>::const_sub_col_type Col;
typedef gmm::linalg_traits<Col>::const_iterator ColIter;

} // namespace

// Constructor
MISolver::MISolver()
{
  // default parameters
  initial_full_solution_ = true;
  iter_full_solution_ = true;
  final_full_solution_ = true;

  direct_rounding_ = false;
  no_rounding_ = false;
  multiple_rounding_ = true;
  gurobi_rounding_ = false;
  cplex_rounding_ = false;

  max_local_iters_ = 100000;
  max_local_error_ = 1e-3;
  max_cg_iters_ = 50;
  max_cg_error_ = 1e-3;

  multiple_rounding_threshold_ = 0.5;

  gurobi_max_time_ = 60;

  noisy_ = 0;
  stats_ = true;

  use_constraint_reordering_ = true;
}

//-----------------------------------------------------------------------------

void MISolver::solve(
    CSCMatrix& _A, Vecd& _x, Vecd& _rhs, Veci& _to_round, bool _fixed_order)
{
  DEB_enter_func;

  DEB_out(6, "# integer    variables: "
                 << _to_round.size() << "\n# continuous variables: "
                 << _x.size() - _to_round.size() << "\n");

  // nothing to solve?
  if (gmm::mat_ncols(_A) == 0 || gmm::mat_nrows(_A) == 0)
    return;

  if (gurobi_rounding_)
    solve_gurobi(_A, _x, _rhs, _to_round);
  else if (cplex_rounding_)
    solve_cplex(_A, _x, _rhs, _to_round);
  else if (no_rounding_ || _to_round.size() == 0)
    solve_no_rounding(_A, _x, _rhs);
  else if (direct_rounding_)
    solve_direct_rounding(_A, _x, _rhs, _to_round);
  else if (multiple_rounding_)
    solve_multiple_rounding(_A, _x, _rhs, _to_round);
  else
    solve_iterative(_A, _x, _rhs, _to_round, _fixed_order);
}

//-----------------------------------------------------------------------------

// inline function...
void MISolver::solve_cplex(CSCMatrix& _A, Vecd& _x, Vecd& _rhs, Veci& _to_round)
{
  DEB_enter_func;
  DEB_out(2, "gurobi_max_time_: " << gurobi_max_time_ << "\n");

#if COMISO_CPLEX_AVAILABLE

  // get round-indices in set
  std::set<int> to_round;
  for (unsigned int i = 0; i < _to_round.size(); ++i)
    to_round.insert(_to_round[i]);

  try
  {

    IloEnv env_;
    IloModel model(env_);

    // set time limite
    //    model.getEnv().set(GRB_DoubleParam_TimeLimit, gurobi_max_time_);

    unsigned int n = _rhs.size();

    // 1. allocate variables
    std::vector<IloNumVar> vars;
    for (unsigned int i = 0; i < n; ++i)
      if (to_round.count(i))
        vars.push_back(IloNumVar(env_, -IloIntMax, IloIntMax, IloNumVar::Int));
      else
        vars.push_back(
            IloNumVar(env_, -IloInfinity, IloInfinity, IloNumVar::Float));

    // 2. setup_energy

    // build objective function from linear system E = x^tAx - 2x^t*rhs
    IloExpr objective(env_);

    for (unsigned int i = 0; i < _A.nc; ++i)
      for (unsigned int j = _A.jc[i]; j < _A.jc[i + 1]; ++j)
      {
        objective += _A.pr[j] * vars[_A.ir[j]] * vars[i];
      }
    for (unsigned int i = 0; i < n; ++i)
      objective -= 2 * _rhs[i] * vars[i];

    // ToDo: objective correction!!!

    //    _A.jc[c+1]
    //    _A.pr[write]
    //    _A.ir[write]
    //    _A.nc
    //    _A.nr

    // minimize
    model.add(IloMinimize(env_, objective));

    // 4. solve
    IloCplex cplex(model);
    cplex.setParam(IloCplex::TiLim, gurobi_max_time_);

    //    // set parameters comparable to CoMISo
    //    {
    //      cplex.setParam(IloCplex::MIPSearch  , 1);  // Traditional
    //      Branch-and-Cut cplex.setParam(IloCplex::NodeSel    , 0);  //
    //      Depth-First cplex.setParam(IloCplex::VarSel     , -1);  // closest
    //      to integer cplex.setParam(IloCplex::MIPEmphasis, 1);  // concentrate
    //      on feasibility
    //    }

    cplex.solve();

    // 5. store result
    _x.resize(n);
    for (unsigned int i = 0; i < n; ++i)
      _x[i] = cplex.getValue(vars[i]);

    DEB_out(2, "CPLEX objective: " << cplex.getObjValue() << "\n");
  }
  catch (IloException& e)
  {
    PROGRESS_RESUME_ABORT; // resume a processed abort request
    DEB_warning(2, "CPLEX Concert exception caught: " << e.getMessage())
  }
  catch (...)
  {
    PROGRESS_RESUME_ABORT; // resume a processed abort request
    DEB_warning(1, "CPLEX Unknown exception caught")
  }

#else
  DEB_out(1, "CPLEX solver is not available, please install it...\n")
#endif
}

//-----------------------------------------------------------------------------

void MISolver::solve_no_rounding(CSCMatrix& _A, Vecd& _x, Vecd& _rhs)
{
  COMISO_THROW_if(
      !direct_solver_.calc_system_gmm(_A), UNSPECIFIED_EIGEN_FAILURE);
  COMISO_THROW_if(!direct_solver_.solve(_x, _rhs), UNSPECIFIED_EIGEN_FAILURE);
}

//-----------------------------------------------------------------------------

void MISolver::resolve(Vecd& _x, Vecd& _rhs) { direct_solver_.solve(_x, _rhs); }

//-----------------------------------------------------------------------------

void MISolver::solve_direct_rounding(
    CSCMatrix& _A, Vecd& _x, Vecd& _rhs, Veci& _to_round)
{
  DEB_enter_func Veci to_round(_to_round);
  // copy to round vector and make it unique
  std::sort(to_round.begin(), to_round.end());
  Veci::iterator last_unique;
  last_unique = std::unique(to_round.begin(), to_round.end());
  size_t r = (size_t)(last_unique - to_round.begin());
  to_round.resize(r);

  // initalize old indices
  Veci old_idx(_rhs.size());
  for (unsigned int i = 0; i < old_idx.size(); ++i)
    old_idx[i] = i;
  direct_solver_.calc_system_gmm(_A);
  direct_solver_.solve(_x, _rhs);

  // check solver performance (only for testing!!!)
  {
    Base::StopWatch sw;

#ifdef COMISO_MISOLVER_PERFORMANCE_TEST
    // performance comparison code
#if (COMISO_SUITESPARSE_SPQR_AVAILABLE)
    {
      sw.start();
      COMISO::SparseQRSolver spqr;
      spqr.calc_system_gmm(_A);
      std::cerr << "SparseQR factor took: " << sw.stop() / 1000.0 << "s\n";
      Vecd x2(_x);
      sw.start();
      spqr.solve(x2, _rhs);
      std::cerr << "SparseQR solve took: " << sw.stop() / 1000.0 << "s\n";
      Vecd res(_x);
      gmm::add(_x, gmm::scaled(x2, -1.0), res);
      std::cerr << "DIFFERENCE IN RESULT: " << gmm::vect_norm2(res)
                << std::endl;
    }
#endif

    // performance comparison code
#if (COMISO_SUITESPARSE_AVAILABLE)
    {
      sw.start();
      COMISO::UMFPACKSolver umf;
      umf.calc_system_gmm(_A);
      std::cerr << "UMFPack factor took: " << sw.stop() / 1000.0 << "s\n";
      Vecd x3(_x);
      sw.start();
      umf.solve(x3, _rhs);
      std::cerr << "UMFPack solve took: " << sw.stop() / 1000.0 << "s\n";
      Vecd res2(_x);
      gmm::add(_x, gmm::scaled(x3, -1.0), res2);
      std::cerr << "UMFPACK DIFFERENCE IN RESULT: " << gmm::vect_norm2(res2)
                << std::endl;
    }

    // performance comparison code
    {
      sw.start();
      COMISO::CholmodSolver chol;
      chol.calc_system_gmm(_A);
      std::cerr << "Choldmod factor took: " << sw.stop() / 1000.0 << "s\n";
      Vecd x4(_x);
      sw.start();
      chol.solve(x4, _rhs);
      std::cerr << "Choldmod solve took: " << sw.stop() / 1000.0 << "s\n";
      Vecd res(_x);
      gmm::add(_x, gmm::scaled(x4, -1.0), res);
      std::cerr << "DIFFERENCE IN RESULT: " << gmm::vect_norm2(res)
                << std::endl;
    }
#endif

#if (COMISO_EIGEN3_AVAILABLE)
    // performance comparison code
    {
      sw.start();
      COMISO::EigenLDLTSolver ldlt;
      ldlt.calc_system_gmm(_A);
      DEB_out(2, "Eigen LDLT factor took: " << sw.stop() / 1000.0 << "s\n")
          Vecd x5(_x);
      sw.start();
      ldlt.solve(x5, _rhs);
      DEB_out(2, "Eigen LDLT solve took: " << sw.stop() / 1000.0 << "s\n")
          Vecd res(_x);
      gmm::add(_x, gmm::scaled(x5, -1.0), res);
      DEB_warning(2, "DIFFERENCE IN RESULT: " << gmm::vect_norm2(res))
    }
#endif
  }
#endif

  // round and eliminate variables
  Vecui elim_i;
  Vecd elim_v;
  for (unsigned int i = 0; i < to_round.size(); ++i)
  {
    _x[to_round[i]] = ROUND(_x[to_round[i]]);
    elim_i.push_back(to_round[i]);
    elim_v.push_back(_x[to_round[i]]);
    // update old idx
    old_idx[to_round[i]] = -1;
  }

  Veci::iterator new_end = std::remove(old_idx.begin(), old_idx.end(), -1);
  old_idx.resize(new_end - old_idx.begin());
  // eliminate vars from linear system
  Vecd xr(_x);
  COMISO_GMM::eliminate_csc_vars2(elim_i, elim_v, _A, xr, _rhs);

  // std::cerr << "size A: " << gmm::mat_nrows(_A) << " " << gmm::mat_ncols(_A)
  // 	    << std::endl;
  // std::cerr << "size x  : " << xr.size() << std::endl;
  // std::cerr << "size rhs: " << _rhs.size() << std::endl;

  // final full solution
  if (gmm::mat_ncols(_A) > 0)
  {
    //    direct_solver_.update_system_gmm(_A);
    direct_solver_.calc_system_gmm(_A);
    direct_solver_.solve(xr, _rhs);
  }

  // store solution values to result vector
  for (unsigned int i = 0; i < old_idx.size(); ++i)
    _x[old_idx[i]] = xr[i];
}

//-----------------------------------------------------------------------------

void MISolver::solve_iterative(
    CSCMatrix& _A, Vecd& _x, Vecd& _rhs, Veci& _to_round, bool _fixed_order)
{
  DEB_enter_func;
  // StopWatch
  Base::StopWatch sw;
  double time_search_next_integer = 0;

  // some statistics
  n_local_ = 0;
  n_cg_ = 0;
  n_full_ = 0;

  // reset cholmod step flag
  cholmod_step_done_ = false;

  Veci to_round(_to_round);
  // if the order is not fixed, uniquify the indices
  if (!_fixed_order)
  {
    // copy to round vector and make it unique
    std::sort(to_round.begin(), to_round.end());
    Veci::iterator last_unique;
    last_unique = std::unique(to_round.begin(), to_round.end());
    size_t r = (size_t)(last_unique - to_round.begin());
    to_round.resize(r);
  }

  // initalize old indices
  Veci old_idx(_rhs.size());
  for (unsigned int i = 0; i < old_idx.size(); ++i)
    old_idx[i] = i;

  if (initial_full_solution_)
  {
    DEB_out_if(noisy_ > 2, 2, "initial full solution\n")
        direct_solver_.calc_system_gmm(_A);
    direct_solver_.solve(_x, _rhs);

    cholmod_step_done_ = true;

    ++n_full_;
  }

  // neighbors for local optimization
  Vecui neigh_i;

  // Vector for reduced solution
  Vecd xr(_x);

  // loop until solution computed
  for (unsigned int i = 0; i < to_round.size(); ++i)
  {
    DEB_out_if(noisy_ > 0, 2,
        "Integer DOF's left: " << to_round.size() - (i + 1)
                               << " ") DEB_out_if(noisy_ > 1, 1,
        "residuum_norm: " << COMISO_GMM::residuum_norm(_A, xr, _rhs) << "\n");

    // index to eliminate
    unsigned int i_best = 0;

    // position in round vector
    unsigned int tr_best = 0;

    if (_fixed_order) // if order is fixed, simply get next index from to_round
    {
      i_best = to_round[i];
    }
    else // else search for best rounding candidate
    {
      sw.start();
      // find index yielding smallest rounding error
      double r_best = FLT_MAX;
      for (unsigned int j = 0; j < to_round.size(); ++j)
      {
        if (to_round[j] != -1)
        {
          int cur_idx = to_round[j];
          double rnd_error = fabs(ROUND(xr[cur_idx]) - xr[cur_idx]);
          if (rnd_error < r_best)
          {
            i_best = cur_idx;
            r_best = rnd_error;
            tr_best = j;
          }
        }
      }
      time_search_next_integer += sw.stop();
    }

    // store rounded value
    double rnd_x = ROUND(xr[i_best]);
    _x[old_idx[i_best]] = rnd_x;

    // compute neighbors
    neigh_i.clear();
    Col col = gmm::mat_const_col(_A, i_best);
    ColIter it = gmm::vect_const_begin(col);
    ColIter ite = gmm::vect_const_end(col);
    for (; it != ite; ++it)
    {
      if (it.index() != i_best)
        neigh_i.push_back(static_cast<int>(it.index()));
    }
    // eliminate var
    COMISO_GMM::fix_var_csc_symmetric(i_best, rnd_x, _A, xr, _rhs);
    to_round[tr_best] = -1;

    // 3-stage update of solution w.r.t. roundings
    // local GS / CG / SparseCholesky
    update_solution(_A, xr, _rhs, neigh_i);
  }

  // final full solution?
  if (final_full_solution_)
  {
    DEB_line_if(noisy_ > 2, 2, "final full solution");

    if (gmm::mat_ncols(_A) > 0)
    {
      if (cholmod_step_done_)
        direct_solver_.update_system_gmm(_A);
      else
        direct_solver_.calc_system_gmm(_A);

      direct_solver_.solve(xr, _rhs);
      ++n_full_;
    }
  }

  // store solution values to result vector
  for (unsigned int i = 0; i < old_idx.size(); ++i)
    _x[old_idx[i]] = xr[i];

  // output statistics
  DEB_out_if(stats_, 2,
      " *** Statistics of MiSo Solver ***"
          << "\n Number of CG    iterations  = " << n_cg_
          << "\n Number of LOCAL iterations  = " << n_local_
          << "\n Number of FULL  iterations  = " << n_full_
          << "\n Number of ROUNDING          = " << _to_round.size()
          << "\n time searching next integer = "
          << time_search_next_integer / 1000.0 << "s\n\n");
}

//-----------------------------------------------------------------------------

void MISolver::update_solution(
    const CSCMatrix& _A, Vecd& _x, const Vecd& _rhs, const Vecui& _neigh_i)
{
  DEB_enter_func;
  bool converged = false; // set to not converged

  if (max_local_iters_ > 0) // compute new solution
  {
    DEB_out(6, "use local iteration ");

    int n_its = max_local_iters_;
    double tolerance = max_local_error_;
    converged =
        siter_.gauss_seidel_local(_A, _x, _rhs, _neigh_i, n_its, tolerance);

    ++n_local_;
  }

  // conjugate gradient
  if (!converged && max_cg_iters_ > 0)
  {
    DEB_out(6, ", cg ");

    int max_cg_iters = max_cg_iters_;
    double tolerance = max_cg_error_;
    converged =
        siter_.conjugate_gradient(_A, _x, _rhs, max_cg_iters, tolerance);

    DEB_out(6, "( converged " << converged << " "
                              << " iters " << max_cg_iters << " "
                              << " res_norm " << tolerance << "\n");
    ++n_cg_;
  }

  if (!converged && iter_full_solution_ && gmm::mat_ncols(_A) > 0)
  {
    DEB_out(6, ", full ");
    if (cholmod_step_done_)
      direct_solver_.update_system_gmm(_A);
    else
    {
      direct_solver_.calc_system_gmm(_A);
      cholmod_step_done_ = true;
    }
    // const_cast<> to work around broken const correctness in Eigen
    direct_solver_.solve(_x, const_cast<Vecd&>(_rhs)); 

    ++n_full_;
  }

  DEB_line(6, "");
}

//-----------------------------------------------------------------------------

void MISolver::solve_multiple_rounding(
    CSCMatrix& _A, Vecd& _x, Vecd& _rhs, const Veci& _to_round)
{
  DEB_time_func_def;
  // some statistics
  n_local_ = 0;
  n_cg_ = 0;
  n_full_ = 0;

  // reset cholmod step flag
  cholmod_step_done_ = false;

  Veci to_round(_to_round);
  { // copy to round vector and make it unique
    std::sort(to_round.begin(), to_round.end());
    const auto last_unique = std::unique(to_round.begin(), to_round.end());
    to_round.resize(last_unique - to_round.begin());
  }

  if (initial_full_solution_)
  {
    DEB_out_if(noisy_ > 2, 2, "initial full solution\n");
    // TODO: we can throw more specific outcomes in the body of the
    // functions below
    COMISO_THROW_if(
        !direct_solver_.calc_system_gmm(_A), UNSPECIFIED_EIGEN_FAILURE);
    COMISO_THROW_if(!direct_solver_.solve(_x, _rhs), UNSPECIFIED_EIGEN_FAILURE);

    cholmod_step_done_ = true;

    ++n_full_;
  }

  //  data context for the main rounding cycle
  Vecui neigh_i;            // neighbors for local optimization
  std::vector<int> tr_best; // best indices to round
  RoundingQueue rndg_queue(multiple_rounding_threshold_); // rounding queue

#ifdef DEB_ON
  Base::StopWatch sw; // additional timer for the search next integer time
  double time_search_next_integer = 0;
#endif // DEB_ON

  // loop until solution computed
  while (!to_round.empty())
  {
    DEB_line(11, "Integer DOF's left: " << to_round.size());
    DEB_line(11, "residuum_norm: " << COMISO_GMM::residuum_norm(_A, _x, _rhs));

    DEB_only(sw.start());
    rndg_queue.clear();

    // find index yielding smallest rounding error
    for (unsigned int j = 0; j < to_round.size(); ++j)
    {
      const auto xr_j = _x[to_round[j]];
      const auto rnd_error = fabs(ROUND(xr_j) - xr_j);
      rndg_queue.add(j, rnd_error);
    }
    rndg_queue.get_ids(tr_best);

    DEB_only(time_search_next_integer += sw.stop());

    // nothing more to do?
    if (tr_best.empty())
      break;

    DEB_line(11, "rounding " << tr_best.size() << " variables simultaneously");

    // clear neigh for local update
    neigh_i.clear();

    for (const auto tr_indx : tr_best)
    {
      const unsigned i_cur = static_cast<unsigned>(to_round[tr_indx]);
      const double rnd_x = ROUND(_x[i_cur]); // store rounded value

      // compute neighbors
      const Col col = gmm::mat_const_col(_A, i_cur);
      for (auto it = gmm::vect_const_begin(col), ite = gmm::vect_const_end(col);
           it != ite; ++it)
      {
        if (it.index() != (unsigned int)i_cur)
          neigh_i.push_back(static_cast<int>(it.index()));
      }
      COMISO_GMM::fix_var_csc_symmetric(
          i_cur, rnd_x, _A, _x, _rhs); // eliminate
      to_round[tr_indx] = -1;
    }

    // 3-stage update of solution w.r.t. roundings
    // local GS / CG / SparseCholesky
    update_solution(_A, _x, _rhs, neigh_i);

    // remove all rounded indices from the to_round[] array
    for (const auto tr_indx : tr_best)
    {
      while (!to_round.empty() && to_round.back() < 0)
        to_round.pop_back(); // remove entries that are already rounded
      if (tr_indx >= to_round.size())
        continue; // already removed
      std::swap(to_round[tr_indx], to_round.back());
      to_round.pop_back();
    }
  }

  // final full solution?
  if (final_full_solution_ && gmm::mat_ncols(_A) > 0)
  {
    DEB_line(3, "final full solution");
    if (cholmod_step_done_)
      direct_solver_.update_system_gmm(_A);
    else
      direct_solver_.calc_system_gmm(_A);

    direct_solver_.solve(_x, _rhs);
    ++n_full_;
  }

  DEB_out_if(stats_, 2, // output statistics
      " *** Statistics of MiSo Solver ***"
          << "\n Number of CG    iterations  = " << n_cg_
          << "\n Number of LOCAL iterations  = " << n_local_
          << "\n Number of FULL  iterations  = " << n_full_
          << "\n Number of ROUNDING          = " << _to_round.size()
          << "\n time searching next integer = "
          << time_search_next_integer / 1000.0 << "s\n\n");
}

//-----------------------------------------------------------------------------

void MISolver::solve_gurobi(
    CSCMatrix& _A, Vecd& _x, Vecd& _rhs, Veci& _to_round)
{
  DEB_enter_func;
#if COMISO_GUROBI_AVAILABLE

  // get round-indices in set
  std::set<int> to_round;
  for (unsigned int i = 0; i < _to_round.size(); ++i)
    to_round.insert(_to_round[i]);

  try
  {
    GRBEnv env = GRBEnv();

    GRBModel model = GRBModel(env);

    // set time limite
    model.getEnv().set(GRB_DoubleParam_TimeLimit, gurobi_max_time_);

    unsigned int n = _rhs.size();

    // 1. allocate variables
    std::vector<GRBVar> vars;
    for (unsigned int i = 0; i < n; ++i)
      if (to_round.count(i))
        vars.push_back(
            model.addVar(-GRB_INFINITY, GRB_INFINITY, 0.0, GRB_INTEGER));
      else
        vars.push_back(
            model.addVar(-GRB_INFINITY, GRB_INFINITY, 0.0, GRB_CONTINUOUS));

    // Integrate new variables
    model.update();

    // 2. setup_energy

    // build objective function from linear system E = x^tAx - 2x^t*rhs
    GRBQuadExpr objective;

    for (unsigned int i = 0; i < _A.nc; ++i)
      for (unsigned int j = _A.jc[i]; j < _A.jc[i + 1]; ++j)
      {
        objective += _A.pr[j] * vars[_A.ir[j]] * vars[i];
      }
    for (unsigned int i = 0; i < n; ++i)
      objective -= 2 * _rhs[i] * vars[i];

    //    _A.jc[c+1]
    //    _A.pr[write]
    //    _A.ir[write]
    //    _A.nc
    //    _A.nr

    // minimize
    model.set(GRB_IntAttr_ModelSense, 1);
    model.setObjective(objective);

    // 4. solve
    model.optimize();

    // 5. store result
    _x.resize(n);
    for (unsigned int i = 0; i < n; ++i)
      _x[i] = vars[i].get(GRB_DoubleAttr_X);

    DEB_out(
        2, "GUROBI objective: " << model.get(GRB_DoubleAttr_ObjVal) << "\n");
  }
  catch (GRBException& e)
  {
    PROGRESS_RESUME_ABORT; // resume a processed abort request
    DEB_warning(2,
        "Error code = " << e.getErrorCode() << "[" << e.getMessage() << "]\n");
  }
  catch (...)
  {
    PROGRESS_RESUME_ABORT; // resume a processed abort request
    DEB_warning(1, "Exception during optimization");
  }

#else
  DEB_out(1, "GUROBI solver is not available, please install it...\n");
#endif
}

//----------------------------------------------------------------------------

void MISolver::show_options_dialog()
{
  DEB_enter_func;
#if (COMISO_QT4_AVAILABLE)
  MISolverDialog* pd = new MISolverDialog(*this);
  pd->exec();
#else
  DEB_warning(1, "Qt not available to show solver dialog!!!");
#endif
}

// end namespace COMISO
} // namespace COMISO