[gecode-users] count/atleast: partial propagation towards y ?

[Mikael Zayenz Lagerkvist]

On Feb 3, 2008 1:08 PM, Mikael Zayenz Lagerkvist <zayenz at gmail.com> wrote:
> On 2 feb 2008, at 18.15, Didier Loiseau wrote:
> > I am trying to post a propagator for the constraint
> >   x' = x or x' = epsilon
> > with x and x' integer variables and epsilon some constant not in
> > dom(x).

> If you are concerned with efficieny, then you could add a custom
> propagator for this constraint.

I realised that I actually implemented this constraint about a year
ago, and dug it out. The code below can be used to propagate "x=y |
x=z"  for integer variables x, y, and z by using Extra::diseq(home, x,
y, z). I haven't tested it thoroughly, but I believe that it works.

Cheers,
Mikael

<code>
/*
 *  Main authors:
 *     Mikael Lagerkvist <lagerkvist at gecode.org>
 *
 *  Copyright:
 *     Mikael Lagerkvist, 2007
 *
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 *  a copy of this software and associated documentation files (the
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 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
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 *  included in all copies or substantial portions of the Software.
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 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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 */

#include "gecode/kernel.hh"
#include "gecode/int.hh"
#include "gecode/iter.hh"
#include "gecode/int/rel.hh"

namespace Extra {
  using namespace ::Gecode;

  /**
   * \brief Domain-consistent propagator for \f$ x_1=x_2\lor x_1=x_3\f$.
   */
  template <class View>
  class DisEq : public TernaryPropagator<View,Int::PC_INT_DOM> {
  protected:
    using TernaryPropagator<View,Int::PC_INT_DOM>::x0;
    using TernaryPropagator<View,Int::PC_INT_DOM>::x1;
    using TernaryPropagator<View,Int::PC_INT_DOM>::x2;

    /// Constructor for cloning \a p
    DisEq(Space* home, bool share, DisEq& p);
    /// Constructor for posting
    DisEq(Space* home, View x0, View x1, View x2);
  public:
    /// Constructor for rewriting \a p during cloning
    DisEq(Space* home, bool share, Propagator& p, View x0, View x1, View x2);
    /// Copy propagator during cloning
    virtual Actor* copy(Space* home, bool share);
    /// Perform propagation
    virtual ExecStatus propagate(Space* home);
    /// Post propagator
    static  ExecStatus post(Space* home, View x0, View x1, View x2);
  };

  template <class View>
  inline
  DisEq<View>::DisEq(Space* home, View x0, View x1, View x2)
    : TernaryPropagator<View,Int::PC_INT_DOM>(home,x0,x1,x2) {}

  template <class View>
  ExecStatus
  DisEq<View>::post(Space* home, View x0, View x1, View x2) {
    (void) new (home) DisEq<View>(home,x0,x1,x2);
    return ES_OK;
  }

  template <class View>
  inline
  DisEq<View>::DisEq(Space* home, bool share, DisEq<View>& p)
    : TernaryPropagator<View,Int::PC_INT_DOM>(home,share,p) {}

  template <class View>
  inline
  DisEq<View>::DisEq(Space* home, bool share, Propagator& p,
                     View x0, View x1, View x2)
    : TernaryPropagator<View,Int::PC_INT_DOM>(home,share,p,x0,x1,x2) {}

  template <class View>
  Actor*
  DisEq<View>::copy(Space* home, bool share) {
    return new (home) DisEq<View>(home,share,*this);
  }

  template <class View>
  ExecStatus
  DisEq<View>::propagate(Space* home) {
    typedef Int::ViewRanges<View> Ranges;

    Ranges vr1(x1), vr2(x2);
    Iter::Ranges::Union<Ranges, Ranges> u12(vr1, vr2);
    GECODE_ME_CHECK(x1.inter_r(home, u12, false));

    if (rtest_nq_dom(x0, x1) == Int::RT_TRUE)
      GECODE_REWRITE(this,
                     (Int::Rel::EqDom<View, View>::post(home, x0, x2)));
    if (rtest_nq_dom(x0, x2) == Int::RT_TRUE)
      GECODE_REWRITE(this,
                     (Int::Rel::EqDom<View, View>::post(home, x0, x1)));

    return x0.assigned() && (x1.assigned() || x2.assigned()) ?
      ES_SUBSUMED(this,home) : ES_FIX;
  }

  /** \brief Post propagator for \f$ x_1=x_2\lor x_1=x_3\f$
   */
  void diseq(Space* home, IntVar x1, IntVar x2, IntVar x3) {
    Int::IntView v1(x1), v2(x2), v3(x3);
    GECODE_ES_FAIL(home,DisEq<Int::IntView>::post(home, v1, v2, v3));
  }
}
</code>



-- 
Mikael Zayenz Lagerkvist, http://www.ict.kth.se/~zayenz/