diff --git a/anabatic/src/Dijkstra.cpp b/anabatic/src/Dijkstra.cpp
index 4deb3ef3..32662c27 100644
--- a/anabatic/src/Dijkstra.cpp
+++ b/anabatic/src/Dijkstra.cpp
@@ -54,11 +54,21 @@ namespace Anabatic {
     string s = "<Vertex " + getString(_id)
              + " connexId:" + getString(_connexId)
              + " d:" + ((_distance == unreached) ? "unreached" : getString(_distance) )
+             + " stamp:" + (hasValidStamp() ? "valid" : "outdated")
+             + " from:" + ((_from) ? "set" : "NULL")
              + ">";
     return s;
   }
 
 
+  void  Vertex::notify ( Vertex* vertex, unsigned int flags )
+  {
+  //Vertex* vertex = getOwner();
+    cdebug.log(111) << "Vertex::notify() " << vertex << endl;
+  // Take into account the GCell modification here.
+  }
+
+
 // -------------------------------------------------------------------
 // Class  :  "Anabatic::Dijkstra".
 
@@ -117,12 +127,13 @@ namespace Anabatic {
 
         _searchArea.merge( rpBb );
 
-        Vertex* vertex = gcell->lookup<Vertex>();
+        Vertex* vertex = gcell->getObserver<Vertex>(GCell::Observable::Vertex);
         if (vertex->getConnexId() < 0) {
           cdebug.log(111) << "Add Vertex: " << vertex << endl;
 
           vertex->setStamp   ( _stamp );
           vertex->setConnexId( _targets.size() );
+          vertex->setFrom    ( NULL );
           Contact* gcontact = vertex->getGContact( _net );
           rp->getBodyHook()->detach();
           rp->getBodyHook()->attach( gcontact->getBodyHook() );
@@ -182,7 +193,7 @@ namespace Anabatic {
           if (edge == current->getFrom()) continue;
           
           GCell*  gneighbor = edge->getOpposite(current->getGCell());
-          Vertex* vneighbor = gneighbor->lookup<Vertex>();
+          Vertex* vneighbor = gneighbor->getObserver<Vertex>(GCell::Observable::Vertex);
 
           cdebug.log(111) << "Neighbor: " << vneighbor << endl;
 
@@ -212,10 +223,21 @@ namespace Anabatic {
       while ( current ) {
         cdebug.log(111) << "| " << current << endl;
 
+        if ( (current->getConnexId() == _connectedsId) and (current->getFrom()) ) {
+          cerr << Error( "Dijkstra::propagate(): There is a loop in the traceback path\n"
+                         "        while routing %s."
+                       , getString(_net).c_str()
+                       ) <<endl;
+          break;
+        }
+
         _sources.insert( current );
         current->setDistance( 0.0 );
         current->setConnexId( _connectedsId );
-        current = current->getPredecessor();
+
+        Vertex* predecessor = current->getPredecessor();
+        current->setFrom( NULL );
+        current = predecessor;
       }
 
       cdebug.tabw(111,-1);
diff --git a/anabatic/src/Edges.cpp b/anabatic/src/Edges.cpp
index 9c6c9164..d93aa483 100644
--- a/anabatic/src/Edges.cpp
+++ b/anabatic/src/Edges.cpp
@@ -32,14 +32,14 @@ namespace Anabatic {
     , _flags(Flags::EastSide)
     , _iedge(0)
   {
-    cdebug.log(110) << "GCell_Edges::Locator::Locator() " << isValid() << endl;
+    // cdebug.log(110) << "GCell_Edges::Locator::Locator() " << isValid() << endl;
     if (_gcell->getEastEdges().empty()) progress();
   }
 
 
   EdgesHL* GCell_Edges::Locator::getClone () const
   {
-    cdebug.log(110) << "GCell_Edges::Locator::getClone()" << endl;
+    // cdebug.log(110) << "GCell_Edges::Locator::getClone()" << endl;
     return new Locator (*this);
   }
 
@@ -60,48 +60,48 @@ namespace Anabatic {
 
   void  GCell_Edges::Locator::progress ()
   {
-    cdebug.log(110) << "GCell_Edges::Locator::progress() [from] " << _flags << " iedge:" << _iedge << endl;
-    cdebug.log(110) << "  East:"  << _gcell->getEastEdges().size()
-                    << "  North:" << _gcell->getNorthEdges().size()
-                    << "  West:"  << _gcell->getWestEdges().size()
-                    << "  South:" << _gcell->getSouthEdges().size() << endl;
-    cdebug.log(110) << this << endl;
+    // cdebug.log(110) << "GCell_Edges::Locator::progress() [from] " << _flags << " iedge:" << _iedge << endl;
+    // cdebug.log(110) << "  East:"  << _gcell->getEastEdges().size()
+    //                 << "  North:" << _gcell->getNorthEdges().size()
+    //                 << "  West:"  << _gcell->getWestEdges().size()
+    //                 << "  South:" << _gcell->getSouthEdges().size() << endl;
+    // cdebug.log(110) << this << endl;
 
     ++_iedge;
     while (_flags) {
       if (_flags.contains(Flags::EastSide)) {
         if (_iedge < _gcell->getEastEdges().size()) break;
-        cdebug.log(110) << "Switching to North side." << endl;
+        // cdebug.log(110) << "Switching to North side." << endl;
         _flags = Flags::NorthSide;
         _iedge = 0;
-        cdebug.log(110) << this << endl;
+        // cdebug.log(110) << this << endl;
         continue;
       }
       if (_flags.contains(Flags::NorthSide))  {
         if (_iedge < _gcell->getNorthEdges().size()) break;
-        cdebug.log(110) << "Switching to West side." << endl;
+        // cdebug.log(110) << "Switching to West side." << endl;
         _flags = Flags::WestSide;
         _iedge = 0;
-        cdebug.log(110) << this << endl;
+        // cdebug.log(110) << this << endl;
         continue;
       }
       if (_flags.contains(Flags::WestSide))  {
         if (_iedge < _gcell->getWestEdges().size()) break;
-        cdebug.log(110) << "Switching to South side." << endl;
+        // cdebug.log(110) << "Switching to South side." << endl;
         _flags = Flags::SouthSide;
         _iedge = 0;
         continue;
       }
       if (_flags.contains(Flags::SouthSide))  {
         if (_iedge < _gcell->getSouthEdges().size()) break;
-        cdebug.log(110) << "All edges done." << endl;
+        // cdebug.log(110) << "All edges done." << endl;
         _flags = 0;
         _iedge = 0;
         break;;
       }
     }
 
-    cdebug.log(110) << "GCell_Edges::Locator::progress() [to]   " << _flags << " iedge:" << _iedge << endl;
+    // cdebug.log(110) << "GCell_Edges::Locator::progress() [to]   " << _flags << " iedge:" << _iedge << endl;
   }
 
 
diff --git a/anabatic/src/GCell.cpp b/anabatic/src/GCell.cpp
index 8589a01d..28c6f30e 100644
--- a/anabatic/src/GCell.cpp
+++ b/anabatic/src/GCell.cpp
@@ -34,6 +34,7 @@ namespace Anabatic {
 
   GCell::GCell ( AnabaticEngine* anabatic, DbU::Unit xmin, DbU::Unit ymin )
     : Super(anabatic->getCell())
+    , _observable()
     , _anabatic  (anabatic)
     , _flags     (Flags::NoFlags)
     , _westEdges ()
@@ -43,7 +44,6 @@ namespace Anabatic {
     , _xmin      (xmin)
     , _ymin      (ymin)
     , _contacts  ()
-    , _lookup    (NULL)
   { }
 
 
@@ -418,6 +418,7 @@ namespace Anabatic {
       cerr << Error( "GCell::_revalidate(): %s, Y Min is greater than Max.", getString(this).c_str() );
 
     _anabatic->_updateLookup( this );
+    _anabatic->getMatrix()->show();
     cdebug.tabw(110,-1);
   }
 
diff --git a/anabatic/src/Matrix.cpp b/anabatic/src/Matrix.cpp
index a9dccdbc..cfcdd980 100644
--- a/anabatic/src/Matrix.cpp
+++ b/anabatic/src/Matrix.cpp
@@ -16,6 +16,7 @@
 
 #include <sstream>
 #include <iostream>
+#include <iomanip>
 #include "hurricane/Cell.h"
 #include "anabatic/Matrix.h"
 #include "anabatic/GCell.h"
@@ -26,6 +27,8 @@ namespace Anabatic {
   using std::cout;
   using std::cerr;
   using std::endl;
+  using std::setw;
+  using std::setfill;
   using std::ostringstream;
   using Hurricane::Error;
 
@@ -46,8 +49,8 @@ namespace Anabatic {
     , _imax  (0)
     , _jmax  (0)
   {
-    _imax = _area.getWidth () / side;
-    _jmax = _area.getHeight() / side;
+    _imax = _area.getWidth () / side + ((_area.getWidth () % side) ? 1 : 0);
+    _jmax = _area.getHeight() / side + ((_area.getHeight() % side) ? 1 : 0);
     _gcells.resize( _imax*_jmax );
   }
 
@@ -60,25 +63,47 @@ namespace Anabatic {
   {
     _area = cell->getAbutmentBox();
     _side = side;
-    _imax = _area.getWidth () / side;
-    _jmax = _area.getHeight() / side;
+    _imax = _area.getWidth () / side + ((_area.getWidth () % side) ? 1 : 0);
+    _jmax = _area.getHeight() / side + ((_area.getHeight() % side) ? 1 : 0);
     _gcells.resize( _imax*_jmax );
+
+    cdebug.log(110) << "Matrix::setCell(): " << this << endl;
   }
 
 
   GCell*  Matrix::getUnder ( DbU::Unit x, DbU::Unit y ) const
-  { int index = xy2index(x,y); return (index < 0) ? NULL : _gcells[index]->getUnder(x,y); }
+  {
+    int index = xy2maxIndex(x,y);
+    cdebug.log(110) << "Matrix::getUnder() ("
+                    << DbU::getValueString(x) << " "
+                    << DbU::getValueString(y) << " " << index << endl;
+    return (index < 0) ? NULL : _gcells[index]->getUnder(x,y);
+  }
 
 
   void  Matrix::updateLookup ( GCell* gcell )
   {
-  //cdebug.log(110,1) << "Matrix::updateLookup(): " << gcell << endl;
+    cdebug.log(110,1) << "Matrix::updateLookup(): " << gcell << endl;
 
-    if (gcell->isFlat()) return;
+    if (gcell->isFlat()) {
+      cdebug.log(110) << " GCell is flat, no update." << endl;
+      cdebug.tabw(110,-1);
+      return;
+    }
 
     Box gcellBb    = gcell->getBoundingBox();
     Box updateArea = _area.getIntersection( gcellBb );
 
+    cdebug.log(110) << "_side            " << _side << endl; 
+    cdebug.log(110) << "_area.getXMin()  " << _area.getXMin() << endl; 
+    cdebug.log(110) << "_area.getYMin()  " << _area.getYMin() << endl; 
+    cdebug.log(110) << "_area.getXMax()  " << _area.getXMax() << endl; 
+    cdebug.log(110) << "_area.getYMax()  " << _area.getYMax() << endl; 
+    cdebug.log(110) << "updateArea.getXMin()  " << updateArea.getXMin() << endl; 
+    cdebug.log(110) << "updateArea.getYMin()  " << updateArea.getYMin() << endl; 
+    cdebug.log(110) << "updateArea.getXMax()  " << updateArea.getXMax() << endl; 
+    cdebug.log(110) << "updateArea.getYMax()  " << updateArea.getYMax() << endl; 
+
     if (updateArea.isEmpty()) {
       cerr << Error( "Matrix::updateLookup(): %s is not under area of %s."
                    , getString(gcell).c_str()
@@ -86,12 +111,20 @@ namespace Anabatic {
                    ) << endl;
     }
 
-    Index  indexMin = Index( this, updateArea.getXMin(), updateArea.getYMin() );
-    Index  indexMax = Index( this, updateArea.getXMax(), updateArea.getYMax() );
+    Index  indexMin = Index::asMin( this, updateArea.getXMin(), updateArea.getYMin() );
+    Index  indexMax = Index::asMax( this, updateArea.getXMax(), updateArea.getYMax() );
     int    xspan    = indexMax.i() - indexMin.i();
 
-  //cdebug.log(110) << "indexMin:" << indexMin << endl;
-  //cdebug.log(110) << "indexMax:" << indexMax << endl;
+    DbU::Unit dx = updateArea.getXMin() - _area.getXMin();
+    DbU::Unit dy = updateArea.getYMin() - _area.getYMin();
+
+    cdebug.log(110) <<  "raw_i:" << (dx / _side + ((dx%_side) ? 1 : 0))
+                    << " raw_j:" << (dy / _side + ((dy%_side) ? 1 : 0)) << endl;
+    cdebug.log(110) << "indexMin:" << indexMin << endl;
+    cdebug.log(110) << "indexMax:" << indexMax << endl;
+    cdebug.log(110) << "xspan:   " << xspan << endl;
+
+    if (not indexMin.valid() or not indexMax.valid()) { cdebug.tabw(110,-1); return; }
 
     int index = indexMin.index();
     while ( index <= indexMax.index() ) {
@@ -101,7 +134,18 @@ namespace Anabatic {
       else                         index += _imax - xspan;
     }
 
-  //cdebug.tabw(110,-1);
+    cdebug.tabw(110,-1);
+  }
+
+
+  void  Matrix::show () const
+  {
+    cdebug.log(111) << this << endl;
+    for ( size_t i=0 ; i<_gcells.size() ; ++i ) {
+      cdebug.log(111) << "[" << setw(3) << setfill('0') << i << setfill(' ') << "] ("
+                      << setw(3) << index2i(i) << ","
+                      << setw(3) << index2j(i) << ") " << _gcells[i] << endl;
+    }
   }
 
 
diff --git a/anabatic/src/anabatic/AnabaticEngine.h b/anabatic/src/anabatic/AnabaticEngine.h
index af3f2f42..8683d40e 100644
--- a/anabatic/src/anabatic/AnabaticEngine.h
+++ b/anabatic/src/anabatic/AnabaticEngine.h
@@ -56,6 +56,7 @@ namespace Anabatic {
       virtual       Configuration*  getConfiguration  ();
       inline        CellViewer*     getViewer         () const;
       inline        void            setViewer         ( CellViewer* );
+      inline  const Matrix*         getMatrix         () const;
       inline  const vector<GCell*>& getGCells         () const;
       inline        GCell*          getSouthWestGCell () const;
       inline        GCell*          getGCellUnder     ( DbU::Unit x, DbU::Unit y ) const;
@@ -98,6 +99,7 @@ namespace Anabatic {
 
   inline CellViewer*           AnabaticEngine::getViewer         () const { return _viewer; }
   inline void                  AnabaticEngine::setViewer         ( CellViewer* viewer ) { _viewer=viewer; }
+  inline const Matrix*         AnabaticEngine::getMatrix         () const { return &_matrix; }
   inline const vector<GCell*>& AnabaticEngine::getGCells         () const { return _gcells; }
   inline GCell*                AnabaticEngine::getSouthWestGCell () const { return _gcells[0]; }
   inline GCell*                AnabaticEngine::getGCellUnder     ( DbU::Unit x, DbU::Unit y ) const { return _matrix.getUnder(x,y); }
diff --git a/anabatic/src/anabatic/Dijkstra.h b/anabatic/src/anabatic/Dijkstra.h
index 60404cbc..cba254c0 100644
--- a/anabatic/src/anabatic/Dijkstra.h
+++ b/anabatic/src/anabatic/Dijkstra.h
@@ -19,6 +19,7 @@
 
 #include <set>
 #include <iomanip>
+#include "hurricane/Observer.h"
 namespace Hurricane {
   class Net;
 }
@@ -29,6 +30,7 @@ namespace Anabatic {
 
   using std::set;
   using std::multiset;
+  using Hurricane::Observer;
   using Hurricane::Net;
   class AnabaticEngine;
 
@@ -44,6 +46,8 @@ namespace Anabatic {
       };
     public:
       static         float           unreached;
+    public:                         
+      static         void            notify         ( Vertex*, unsigned flags );
     public:                         
              inline                  Vertex         ( GCell* );
              inline                  Vertex         ( size_t id );
@@ -69,29 +73,33 @@ namespace Anabatic {
                                      Vertex         ( const Vertex& );
                      Vertex&         operator=      ( const Vertex& );
     private:
-      size_t  _id;
-      GCell*  _gcell;
-      int     _connexId;
-      int     _stamp;
-      float   _distance;
-      Edge*   _from;
+      size_t            _id;
+      GCell*            _gcell;
+      Observer<Vertex>  _observer;
+      int               _connexId;
+      int               _stamp;
+      float             _distance;
+      Edge*             _from;
   };
 
 
   inline Vertex::Vertex ( GCell* gcell )
     : _id      (gcell->getId())
     , _gcell   (gcell)
+    , _observer(this)
     , _connexId(-1)
     , _stamp   (-1)
     , _distance(unreached)
     , _from    (NULL)
   {
-    gcell->setLookup<Vertex>( this );
+  //gcell->setLookup<Vertex>( this );
+    gcell->setObserver( GCell::Observable::Vertex, &_observer );
   }
 
   inline Vertex::Vertex ( size_t id )
     : _id      (id)
     , _gcell   (NULL)
+    , _observer((Vertex*)0x1)  // To trick the NULL detection.
     , _connexId(-1)
     , _stamp   (-1)
     , _distance(unreached)
@@ -114,11 +122,12 @@ namespace Anabatic {
   inline void             Vertex::setConnexId    ( int id ) { _connexId=id; }
 
   inline Vertex* Vertex::getPredecessor () const
-  { return (hasValidStamp() and _from) ? _from->getOpposite(_gcell)->lookup<Vertex>() : NULL; }
+  { return (hasValidStamp() and _from) ? _from->getOpposite(_gcell)->getObserver<Vertex>(GCell::Observable::Vertex) : NULL; }
 
   inline bool  Vertex::CompareById::operator() ( const Vertex* lhs, const Vertex* rhs )
   { return lhs->getId() < rhs->getId(); }
 
+
   typedef  set<Vertex*,Vertex::CompareById>  VertexSet;
 
 
diff --git a/anabatic/src/anabatic/Edges.h b/anabatic/src/anabatic/Edges.h
index bca4b254..347d61c7 100644
--- a/anabatic/src/anabatic/Edges.h
+++ b/anabatic/src/anabatic/Edges.h
@@ -89,7 +89,7 @@ namespace Anabatic {
     , _flags(locator._flags)
     , _iedge(locator._iedge)
   {
-    cdebug.log(110) << "GCell_Edges::Locator::Locator(const Locator&)" << std::endl;
+    // cdebug.log(110) << "GCell_Edges::Locator::Locator(const Locator&)" << std::endl;
   }
 
 
diff --git a/anabatic/src/anabatic/GCell.h b/anabatic/src/anabatic/GCell.h
index e977723d..1c742fef 100644
--- a/anabatic/src/anabatic/GCell.h
+++ b/anabatic/src/anabatic/GCell.h
@@ -34,6 +34,8 @@ namespace Anabatic {
 
   using std::string;
   using std::vector;
+  using Hurricane::StaticObservable;
+  using Hurricane::BaseObserver;
   using Hurricane::Name;
   using Hurricane::Record;
   using Hurricane::DbU;
@@ -54,6 +56,17 @@ namespace Anabatic {
   class GCell : public ExtensionGo {
     public:
       typedef ExtensionGo  Super;
+    public:
+      class Observable : public StaticObservable<1> {
+        public:
+          enum Indexes { Vertex = 0
+                       };
+        public:
+          inline             Observable ();
+        private:
+                             Observable ( const StaticObservable& );
+                 Observable& operator=  ( const StaticObservable& );
+      };
     public:
       static        Box             getBorder            ( const GCell*, const GCell* );
     public:                         
@@ -88,10 +101,6 @@ namespace Anabatic {
                     GCell*          vcut                 ( DbU::Unit x );
                     bool            doGrid               ();
                     Contact*        getGContact          ( Net* );
-      template<typename Type>
-      inline        void            setLookup            ( Type* decorator );
-      template<typename Type>
-      inline        Type*           lookup               () const;
     // Misc. functions.
       inline const  Flags&          flags                () const;
       inline        Flags&          flags                ();
@@ -102,27 +111,33 @@ namespace Anabatic {
                     void            _revalidate          ();
                     void            _moveEdges           ( GCell* dest, size_t ibegin, Flags flags );
     public:                                
+    // Observers.
+      inline        void            setObserver          ( size_t slot, BaseObserver* );
+      template<typename OwnerT>
+      inline        OwnerT*         getObserver          ( size_t slot );
+      inline        void            notify               ( unsigned int flags );
     // ExtensionGo support.                
-      inline  const Name&         staticGetName        (); 
-      virtual const Name&         getName              () const;
-      virtual       void          translate            ( const DbU::Unit&, const DbU::Unit& );
-      virtual       Box           getBoundingBox       () const;
-    public:                                            
-    // Inspector support.                              
-      virtual       string        _getTypeName         () const;
-      virtual       string        _getString           () const;
-      virtual       Record*       _getRecord           () const;
-    protected:                                         
-                                  GCell                ( AnabaticEngine*, DbU::Unit xmin, DbU::Unit ymin );
-      virtual                    ~GCell                ();
-                    GCell*        _create              ( DbU::Unit xmin, DbU::Unit ymin );
-      virtual       void          _postCreate          ();
-      virtual       void          _preDestroy          ();
-    private:
-                                  GCell                ( const GCell& );
-                    GCell&        operator=            ( const GCell& );
+      inline  const Name&           staticGetName        (); 
+      virtual const Name&           getName              () const;
+      virtual       void            translate            ( const DbU::Unit&, const DbU::Unit& );
+      virtual       Box             getBoundingBox       () const;
+    public:                                              
+    // Inspector support.                                
+      virtual       string          _getTypeName         () const;
+      virtual       string          _getString           () const;
+      virtual       Record*         _getRecord           () const;
+    protected:                                           
+                                    GCell                ( AnabaticEngine*, DbU::Unit xmin, DbU::Unit ymin );
+      virtual                      ~GCell                ();
+                    GCell*          _create              ( DbU::Unit xmin, DbU::Unit ymin );
+      virtual       void            _postCreate          ();
+      virtual       void            _preDestroy          ();
+    private:                        
+                                    GCell                ( const GCell& );
+                    GCell&          operator=            ( const GCell& );
     private:
       static  Name             _extensionName;
+              Observable       _observable;
               AnabaticEngine*  _anabatic;
               Flags            _flags;
               vector<Edge*>    _westEdges;
@@ -132,7 +147,6 @@ namespace Anabatic {
               DbU::Unit        _xmin;
               DbU::Unit        _ymin;
               vector<Contact*> _contacts;
-              void*            _lookup;
   };
 
 
@@ -172,11 +186,17 @@ namespace Anabatic {
     return Interval( getXMin(), getXMax() );
   }
 
-  template<typename Type>
-  inline void  GCell::setLookup ( Type* decorator ) { _lookup=reinterpret_cast<void*>(decorator); }
+  inline void  GCell::setObserver ( size_t slot, BaseObserver* observer )
+  { _observable.setObserver( slot, observer ); }
 
-  template<typename Type>
-  inline Type* GCell::lookup () const { return reinterpret_cast<Type*>( _lookup ); }
+  template<typename OwnerT>
+  inline OwnerT* GCell::getObserver ( size_t slot )
+  { return _observable.getObserver<OwnerT>(slot); }
+
+  inline void  GCell::notify ( unsigned int flags )
+  { _observable.notify( flags ); }
+
+  inline GCell::Observable::Observable () : StaticObservable<1>() { }
 
 
 // -------------------------------------------------------------------
diff --git a/anabatic/src/anabatic/Matrix.h b/anabatic/src/anabatic/Matrix.h
index b6357c27..cf603a4b 100644
--- a/anabatic/src/anabatic/Matrix.h
+++ b/anabatic/src/anabatic/Matrix.h
@@ -43,11 +43,14 @@ namespace Anabatic {
   class Matrix {
     public:
       class Index {
+        public:
+          static inline Matrix::Index  asMin ( Matrix*, DbU::Unit x, DbU::Unit y );
+          static inline Matrix::Index  asMax ( Matrix*, DbU::Unit x, DbU::Unit y );
+          static inline Matrix::Index  asMin ( Matrix*, Point position );
+          static inline Matrix::Index  asMax ( Matrix*, Point position );
         public:
           inline               Index  ( Matrix*, int index );
           inline               Index  ( Matrix*, int i, int j );
-          inline               Index  ( Matrix*, DbU::Unit x, DbU::Unit y );
-          inline               Index  ( Matrix*, Point position );
           inline       Matrix* matrix () const;
           inline const int&    index  () const;
           inline       int&    index  ();
@@ -78,8 +81,10 @@ namespace Anabatic {
       inline  int        index2i      ( const Index& ) const;
       inline  int        index2j      ( const Index& ) const;
       inline  int        ij2index     ( int i, int j ) const;
-      inline  int        xy2index     ( DbU::Unit x, DbU::Unit y ) const;
-      inline  int        xy2index     ( Point ) const;
+      inline  int        xy2minIndex  ( DbU::Unit x, DbU::Unit y ) const;
+      inline  int        xy2minIndex  ( Point ) const;
+      inline  int        xy2maxIndex  ( DbU::Unit x, DbU::Unit y ) const;
+      inline  int        xy2maxIndex  ( Point ) const;
       inline  Index&     west         ( Index& ) const;
       inline  Index&     east         ( Index& ) const;
       inline  Index&     south        ( Index& ) const;
@@ -88,6 +93,7 @@ namespace Anabatic {
       inline  GCell*     getUnder     ( Point ) const;
               void       setCell      ( Cell*, DbU::Unit side );
               void       updateLookup ( GCell* );
+              void       show         () const;
     // Inspector support.                            
       virtual Record*    _getRecord   () const;
       virtual string     _getString   () const;
@@ -127,14 +133,29 @@ namespace Anabatic {
   {
     if ((i < 0) or (i >= _imax)) return -1;
     if ((j < 0) or (j >= _jmax)) return -1;
-    return j*_jmax + i;
+    return j*_imax + i;
   }
 
-  inline int  Matrix::xy2index ( DbU::Unit x, DbU::Unit y ) const
-  { return ij2index( (x - _area.getXMin()) / _side, (y - _area.getYMin()) / _side ); }
+  inline int  Matrix::xy2minIndex ( DbU::Unit x, DbU::Unit y ) const
+  {
+    DbU::Unit dx = x - _area.getXMin();
+    DbU::Unit dy = y - _area.getYMin();
+    return ij2index( dx / _side + ((dx%_side) ? 1 : 0)
+                   , dy / _side + ((dy%_side) ? 1 : 0) );
+  }
 
-  inline int  Matrix::xy2index ( Point p ) const
-  { return xy2index( p.getX(), p.getY() ); }
+  inline int  Matrix::xy2minIndex ( Point p ) const
+  { return xy2minIndex( p.getX(), p.getY() ); }
+
+  inline int  Matrix::xy2maxIndex ( DbU::Unit x, DbU::Unit y ) const
+  {
+    DbU::Unit dx = x - _area.getXMin();
+    DbU::Unit dy = y - _area.getYMin();
+    return ij2index( dx / _side, dy / _side );
+  }
+
+  inline int  Matrix::xy2maxIndex ( Point p ) const
+  { return xy2maxIndex( p.getX(), p.getY() ); }
 
   inline Matrix::Index& Matrix::west ( Matrix::Index& index ) const
   {
@@ -186,11 +207,13 @@ namespace Anabatic {
 
 // Matrix::Index inline functions.
 
-  inline  Matrix::Index::Index ( Matrix* m, int index )                : _matrix(m), _index(index) { }
-  inline  Matrix::Index::Index ( Matrix* m, int i, int j )             : _matrix(m), _index(m->ij2index(i,j)) { }
-  inline  Matrix::Index::Index ( Matrix* m, DbU::Unit x, DbU::Unit y ) : _matrix(m), _index(m->xy2index(x,y)) { }
-  inline  Matrix::Index::Index ( Matrix* m, Point position )           : _matrix(m), _index(m->xy2index(position)) { }
+  inline  Matrix::Index::Index ( Matrix* m, int index )    : _matrix(m), _index(index) { }
+  inline  Matrix::Index::Index ( Matrix* m, int i, int j ) : _matrix(m), _index(m->ij2index(i,j)) { }
 
+  inline       Matrix::Index   Matrix::Index::asMin  ( Matrix* m, DbU::Unit x, DbU::Unit y ) { return Index( m, m->xy2minIndex(x,y) ); }
+  inline       Matrix::Index   Matrix::Index::asMin  ( Matrix* m, Point position )           { return Index( m, m->xy2minIndex(position) ); }
+  inline       Matrix::Index   Matrix::Index::asMax  ( Matrix* m, DbU::Unit x, DbU::Unit y ) { return Index( m, m->xy2maxIndex(x,y) ); }
+  inline       Matrix::Index   Matrix::Index::asMax  ( Matrix* m, Point position )           { return Index( m, m->xy2maxIndex(position) ); }
   inline       Matrix*         Matrix::Index::matrix () const { return _matrix; }
   inline const int&            Matrix::Index::index  () const { return _index; }
   inline       int&            Matrix::Index::index  ()       { return _index; }