CoinUtils/src/CoinPresolveDupcol.hpp

/* $Id: CoinPresolveDupcol.hpp 2083 2019-01-06 19:38:09Z unxusr $ */
// Copyright (C) 2002, International Business Machines
// Corporation and others.  All Rights Reserved.
// This code is licensed under the terms of the Eclipse Public License (EPL).

#ifndef CoinPresolveDupcol_H
#define CoinPresolveDupcol_H

#include "CoinPresolveMatrix.hpp"

/*!
  \file
*/

#define DUPCOL 10

/*! \class dupcol_action
    \brief Detect and remove duplicate columns

    The general technique is to sum the coefficients a_(*,j) of each column.
    Columns with identical sums are duplicates. The obvious problem is that,
    <i>e.g.</i>, [1 0 1 0] and [0 1 0 1] both add to 2. To minimize the
    chances of false positives, the coefficients of each row are multipled by
    a random number r_i, so that we sum r_i*a_ij.

   Candidate columns are checked to confirm they are identical. Where the
   columns have the same objective coefficient, the two are combined. If the
   columns have different objective coefficients, complications ensue. In order
   to remove the duplicate, it must be possible to fix the variable at a bound.
*/

class dupcol_action : public CoinPresolveAction {
  dupcol_action();
  dupcol_action(const dupcol_action &rhs);
  dupcol_action &operator=(const dupcol_action &rhs);

  struct action {
    double thislo;
    double thisup;
    double lastlo;
    double lastup;
    int ithis;
    int ilast;

    double *colels;
    int nincol;
  };

  const int nactions_;
  // actions_ is owned by the class and must be deleted at destruction
  const action *const actions_;

  dupcol_action(int nactions, const action *actions,
    const CoinPresolveAction *next)
    : CoinPresolveAction(next)
    , nactions_(nactions)
    , actions_(actions)
  {
  }

public:
  const char *name() const;

  static const CoinPresolveAction *presolve(CoinPresolveMatrix *prob,
    const CoinPresolveAction *next);

  void postsolve(CoinPostsolveMatrix *prob) const;

  virtual ~dupcol_action();
};

/*! \class duprow_action
    \brief Detect and remove duplicate rows

    The algorithm to detect duplicate rows is as outlined for dupcol_action.

    If the feasible interval for one constraint is strictly contained in the
    other, the tighter (contained) constraint is kept. If the feasible
    intervals are disjoint, the problem is infeasible. If the feasible
    intervals overlap, both constraints are kept.

    duprow_action is definitely a work in progress; #postsolve is
    unimplemented.
    This doesn't matter as it uses useless_constraint.
*/

class duprow_action : public CoinPresolveAction {
  struct action {
    int row;
    double lbound;
    double ubound;
  };

  const int nactions_;
  const action *const actions_;

  duprow_action()
    : CoinPresolveAction(NULL)
    , nactions_(0)
    , actions_(NULL)
  {
  }
  duprow_action(int nactions,
    const action *actions,
    const CoinPresolveAction *next)
    : CoinPresolveAction(next)
    , nactions_(nactions)
    , actions_(actions)
  {
  }

public:
  const char *name() const;

  static const CoinPresolveAction *presolve(CoinPresolveMatrix *prob,
    const CoinPresolveAction *next);

  void postsolve(CoinPostsolveMatrix *prob) const;

  //~duprow_action() { delete[]actions_; }
};

class duprow3_action : public CoinPresolveAction {
  struct action {
    int row;
    double lbound;
    double ubound;
  };

  const int nactions_;
  const action *const actions_;

  duprow3_action()
    : CoinPresolveAction(NULL)
    , nactions_(0)
    , actions_(NULL)
  {
  }
  duprow3_action(int nactions,
    const action *actions,
    const CoinPresolveAction *next)
    : CoinPresolveAction(next)
    , nactions_(nactions)
    , actions_(actions)
  {
  }

public:
  const char *name() const;

  static const CoinPresolveAction *presolve(CoinPresolveMatrix *prob,
    const CoinPresolveAction *next);

  void postsolve(CoinPostsolveMatrix *prob) const;

  //~duprow_action() { delete[]actions_; }
};

/*! \class gubrow_action
    \brief Detect and remove entries whose sum is known

    If we have an equality row where all entries same then
    For other rows where all entries for that equality row are same
    then we can delete entries and modify rhs
    gubrow_action is definitely a work in progress; #postsolve is
    unimplemented.
*/

class gubrow_action : public CoinPresolveAction {
  struct action {
    double rhs;
    // last is row itself
    int *deletedRow;
    double *rowels;
    int *indices; // indices in gub row
    int nDrop;
    int ninrow;
  };

  const int nactions_;
  const action *const actions_;

  //gubrow_action():CoinPresolveAction(NULL),nactions_(0),actions_(NULL) {}
  gubrow_action(int nactions,
    const action *actions,
    const CoinPresolveAction *next)
    : CoinPresolveAction(next)
    , nactions_(nactions)
    , actions_(actions)
  {
  }

public:
  const char *name() const;

  static const CoinPresolveAction *presolve(CoinPresolveMatrix *prob,
    const CoinPresolveAction *next);

  void postsolve(CoinPostsolveMatrix *prob) const;

  virtual ~gubrow_action();
};

/*! \class twoxtwo_action
    \brief Detect interesting 2 by 2 blocks

    If a variable has two entries and for each row there are only
    two entries with same other variable then we can get rid of
    one constraint and modify costs.

    This is a work in progress - I need more examples
*/

class twoxtwo_action : public CoinPresolveAction {
  struct action {
    double lbound_row;
    double ubound_row;
    double lbound_col;
    double ubound_col;
    double cost_col;
    double cost_othercol;
    int row;
    int col;
    int othercol;
  };

  const int nactions_;
  const action *const actions_;

  twoxtwo_action()
    : CoinPresolveAction(NULL)
    , nactions_(0)
    , actions_(NULL)
  {
  }
  twoxtwo_action(int nactions,
    const action *actions,
    const CoinPresolveAction *next)
    : CoinPresolveAction(next)
    , nactions_(nactions)
    , actions_(actions)
  {
  }

public:
  const char *name() const;

  static const CoinPresolveAction *presolve(CoinPresolveMatrix *prob,
    const CoinPresolveAction *next);

  void postsolve(CoinPostsolveMatrix *prob) const;

  ~twoxtwo_action() { delete[] actions_; }
};

#endif

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