exprSub.cpp

Go to the documentation of this file.

/* $Id: exprSub.cpp 1147 2015-05-04 14:01:51Z stefan $
 *
 * Name:    exprSub.cpp
 * Author:  Pietro Belotti
 * Purpose: definition of subtractions
 *
 * (C) Carnegie-Mellon University, 2006-10.
 * This file is licensed under the Eclipse Public License (EPL)
 */

#include "CouenneExprSub.hpp"
#include "CouenneExprConst.hpp"
#include "CouenneExprOpp.hpp"
#include "CouennePrecisions.hpp"

#include "CoinFinite.hpp"

using namespace Couenne;

// simplify subtractions

expression *exprSub::simplify () {

  exprOp:: simplify ();

  // check for (f(x) - f(x))
  if (arglist_ [0] -> compare (*(arglist_ [1])) == 0) {

    // delete arglist_ [0]; arglist_ [0] = NULL;
    // delete arglist_ [1]; arglist_ [1] = NULL;

    return new exprConst (0.);
  }

  // check for other special cases
  if ((*arglist_) -> Type () == CONST) { // expr = c1 - f2 

    CouNumber c0 = (*arglist_) -> Value ();

    if (arglist_ [1] -> Type () == CONST) { // expr = c1 - c2

      CouNumber c1 = arglist_ [1] -> Value ();

      // delete arglist_ [0]; arglist_ [0] = NULL;
      // delete arglist_ [1]; arglist_ [1] = NULL;

      return new exprConst (c0 - c1);
    }
    else if (fabs (c0) == 0.) { // expr = opp (f2)

      expression *ret = new exprOpp (arglist_ [1]);
      //      delete arglist_ [0];
      arglist_ [1] = NULL;
      return ret;
    }
  }
  else // only need to check if f2 == 0

    if ((arglist_ [1] -> Type () == CONST) &&
        (fabs (arglist_ [1] -> Value ()) < COUENNE_EPS_SIMPL)) {
      // expr = f1 - 0 --> return f1

      expression *ret = arglist_ [0];
      //delete arglist_ [1];
      arglist_ [0] = NULL;
      return ret;
    }

  return NULL;
}


// differentiate product of expressions

expression *exprSub::differentiate (int index) {

  expression **arglist = new expression * [nargs_];

  for (int i = 0; i < nargs_; i++)
    if (arglist_ [i] -> dependsOn (index))
         arglist [i] = arglist_ [i] -> differentiate (index);
    else arglist [i] = new exprConst (0.);

  return new exprSub (arglist, nargs_);
}


// Get lower and upper bound of an expression (if any)
void exprSub::getBounds (expression *&lb, expression *&ub) {

  expression **alsl = new expression * [2];
  expression **alsu = new expression * [2];

  arglist_ [0] -> getBounds (alsl [0], alsu [0]);
  arglist_ [1] -> getBounds (alsu [1], alsl [1]);

  lb = new exprSub (alsl, 2);
  ub = new exprSub (alsu, 2);
}


// Get value of lower and upper bound of an expression (if any)
void exprSub::getBounds (CouNumber &lb, CouNumber &ub) {

  CouNumber lba0, uba0, lba1, uba1;

  arglist_ [0] -> getBounds (lba0, uba0);
  arglist_ [1] -> getBounds (lba1, uba1);

  lb = ((lba0 < -COUENNE_INFINITY) || (uba1 >  COUENNE_INFINITY)) ?
    -COUENNE_INFINITY :
    (lba0 - uba1);

  ub = ((uba0 >  COUENNE_INFINITY) || (lba1 < -COUENNE_INFINITY)) ?
    COUENNE_INFINITY :
    (uba0 - lba1);
}



bool exprSub::impliedBound (int wind, CouNumber *l, CouNumber *u, t_chg_bounds *chg, enum auxSign sign) {

  // caution, xi or yi might be -1
  int xi = arglist_ [0] -> Index (),
      yi = arglist_ [1] -> Index ();

  if ((xi == -1) && (yi == -1)) // both x and y are constant
    return false;

  CouNumber xl, xu, yl, yu, 
    wl = sign == expression::AUX_GEQ ? -COIN_DBL_MAX : l [wind], 
    wu = sign == expression::AUX_LEQ ?  COIN_DBL_MAX : u [wind];

  if (xi==-1) xl =         xu = arglist_ [0] -> Value ();
  else       {xl = l [xi]; xu = u [xi];}

  if (yi==-1) yl =         yu = arglist_ [1] -> Value ();
  else       {yl = l [yi]; yu = u [yi];}

  bool res = false;

  // w >= l

  bool 
    xInt = arglist_ [0] -> isInteger (),
    yInt = arglist_ [1] -> isInteger ();

  if (wl > -COUENNE_INFINITY) {

    if ((xi>=0) && (updateBound (-1, l + xi, xInt ? ceil  (yl + wl - COUENNE_EPS) : (yl + wl)))) {
      res = true;
      chg [xi].setLower(t_chg_bounds::CHANGED);
    }

    if ((yi>=0) && (updateBound (+1, u + yi, yInt ? floor (xu - wl + COUENNE_EPS) : (xu - wl)))) {
      res = true;
      chg [yi].setUpper(t_chg_bounds::CHANGED);
    }
  }

  // w <= u

  if (wu < COUENNE_INFINITY) {

    if ((xi>=0) && (updateBound (+1, u + xi, xInt ? floor (yu + wu + COUENNE_EPS) : (yu + wu)))) {
      res = true;
      chg [xi].setUpper(t_chg_bounds::CHANGED);
    }

    if ((yi>=0) && (updateBound (-1, l + yi, yInt ? ceil (xl - wu - COUENNE_EPS) : (xl - wu)))) {
      res = true;
      chg [yi].setLower(t_chg_bounds::CHANGED);
    }
  }

  return res;
}