]> git.uio.no Git - u/mrichter/AliRoot.git/blobdiff - MUON/AliMUONTrackReconstructorK.cxx
Changed default OCDB from 2009 to 2010
[u/mrichter/AliRoot.git] / MUON / AliMUONTrackReconstructorK.cxx
index cb3bcc1720e9fc06d0b8c6dc3fb62cdbd326b0fb..8c265ba3b3bd0b1905b98497cf0a369dd5924559 100644 (file)
@@ -37,6 +37,7 @@
 #include "AliMUONTrack.h"
 #include "AliMUONTrackParam.h"
 #include "AliMUONTrackExtrap.h"
+#include "AliMUONRecoParam.h"
 
 #include "AliMpArea.h"
 
@@ -64,14 +65,15 @@ AliMUONTrackReconstructorK::~AliMUONTrackReconstructorK()
 } 
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::MakeTrackCandidates(AliMUONVClusterStore& clusterStore)
+Bool_t AliMUONTrackReconstructorK::MakeTrackCandidates(AliMUONVClusterStore& clusterStore)
 {
-  /// To make track candidates (assuming linear propagation if the flag fgkMakeTrackCandidatesFast is set to kTRUE):
+  /// To make track candidates (assuming linear propagation if AliMUONRecoParam::MakeTrackCandidatesFast() return kTRUE):
   /// Start with segments station(1..) 4 or 5 then follow track in station 5 or 4.
-  /// Good candidates are made of at least three clusters if both station are requested (two otherwise).
-  /// Keep only best candidates or all of them according to the flag fgkTrackAllTracks.
+  /// Good candidates are made of at least three clusters if both stations are requested (two otherwise).
+  /// Keep only best candidates or all of them according to the flag AliMUONRecoParam::TrackAllTracks().
   
   TClonesArray *segments;
+  AliMUONObjectPair *segment;
   AliMUONTrack *track;
   Int_t iCandidate = 0;
   Bool_t clusterFound;
@@ -100,82 +102,83 @@ void AliMUONTrackReconstructorK::MakeTrackCandidates(AliMUONVClusterStore& clust
     segments = MakeSegmentsBetweenChambers(clusterStore, 2*istat, 2*istat+1);
     
     // Loop over segments
-    for (Int_t iseg=0; iseg<segments->GetEntriesFast(); iseg++) {
+    for (Int_t iSegment=0; iSegment<segments->GetEntriesFast(); iSegment++) {
       AliDebug(1,Form("Making primary candidate(1..) %d",++iCandidate));
+      segment = (AliMUONObjectPair*) segments->UncheckedAt(iSegment);
       
       // Transform segments to tracks and put them at the end of fRecTracksPtr
-      track = new ((*fRecTracksPtr)[fRecTracksPtr->GetLast()+1]) AliMUONTrack((AliMUONObjectPair*)((*segments)[iseg]),GetRecoParam()->GetBendingVertexDispersion());
+      track = new ((*fRecTracksPtr)[fRecTracksPtr->GetLast()+1]) AliMUONTrack(segment,GetRecoParam()->GetBendingVertexDispersion());
       fNRecTracks++;
       
       // Look for compatible cluster(s) in the other station
-      if (GetRecoParam()->MakeTrackCandidatesFast())
-       clusterFound = FollowLinearTrackInStation(*track, clusterStore, 7-istat);
-      else {
-        // First recompute track parameters and covariances on station(1..) 5 using Kalman filter
-        // (to make sure all tracks are treated in the same way)
-        if (istat == 4) RetraceTrack(*track, kTRUE);
-       clusterFound = FollowTrackInStation(*track, clusterStore, 7-istat);
-      }
+      if (GetRecoParam()->MakeTrackCandidatesFast()) clusterFound = FollowLinearTrackInStation(*track, clusterStore, 7-istat);
+      else clusterFound = FollowTrackInStation(*track, clusterStore, 7-istat);
       
       // Remove track if no cluster found on a requested station
-      if (!clusterFound) {
-       if (GetRecoParam()->RequestStation(7-istat)) {
-          fRecTracksPtr->Remove(track);
-         fNRecTracks--;
-       } else if (istat == 3 && !GetRecoParam()->MakeTrackCandidatesFast()) {
-         // update track parameters and covariances using Kalman filter
-         RetraceTrack(*track, kTRUE);
+      // or abort tracking if there are too many candidates
+      if (GetRecoParam()->RequestStation(7-istat)) {
+       if (!clusterFound) {
+         fRecTracksPtr->Remove(track);
+         fNRecTracks--;
+       } else if (fNRecTracks > GetRecoParam()->GetMaxTrackCandidates()) {
+         AliError(Form("Too many track candidates (%d tracks). Stop tracking.", fNRecTracks));
+         delete segments;
+         return kFALSE;
+       }
+      } else {
+       if ((fNRecTracks + segments->GetEntriesFast() - iSegment - 1) > GetRecoParam()->GetMaxTrackCandidates()) {
+         AliError(Form("Too many track candidates (%d tracks). Stop tracking.", fNRecTracks + segments->GetEntriesFast() - iSegment - 1));
+         delete segments;
+         return kFALSE;
        }
       }
       
     }
+    
     // delete the array of segments
     delete segments;
   }
   
+  // Keep all different tracks if required
+  if (GetRecoParam()->TrackAllTracks()) RemoveIdenticalTracks();
   
-  // Retrace tracks using Kalman filter and remove bad ones
-  if (GetRecoParam()->MakeTrackCandidatesFast()) {
-    fRecTracksPtr->Compress(); // this is essential before checking tracks
+  // Retrace tracks using Kalman filter and select them if needed
+  Int_t nCurrentTracks = fRecTracksPtr->GetLast()+1;
+  for (Int_t iRecTrack = 0; iRecTrack < nCurrentTracks; iRecTrack++) {
+    track = (AliMUONTrack*) fRecTracksPtr->UncheckedAt(iRecTrack);
     
-    Int_t currentNRecTracks = fNRecTracks;
-    for (Int_t iRecTrack = 0; iRecTrack < currentNRecTracks; iRecTrack++) {
-      track = (AliMUONTrack*) fRecTracksPtr->UncheckedAt(iRecTrack);
-      
-      // Recompute track parameters and covariances using Kalman filter
-      RetraceTrack(*track,kTRUE);
-      
-      // Remove the track if the normalized chi2 is too high
-      if (track->GetNormalizedChi2() > GetRecoParam()->GetSigmaCutForTracking() *
-                                      GetRecoParam()->GetSigmaCutForTracking()) {
-        fRecTracksPtr->Remove(track);
-        fNRecTracks--;
-      }
-      
+    // skip empty slots
+    if(!track) continue;
+    
+    // retrace tracks using Kalman filter and remove the ones for which extrap failed or that are out of limits
+    if (!RetraceTrack(*track,kTRUE) || !IsAcceptable(*((AliMUONTrackParam*)track->GetTrackParamAtCluster()->First()))) {
+      fRecTracksPtr->Remove(track);
+      fNRecTracks--;
     }
     
   }
   
-  fRecTracksPtr->Compress(); // this is essential before checking tracks
-  
-  // Keep all different tracks or only the best ones as required
-  if (GetRecoParam()->TrackAllTracks()) RemoveIdenticalTracks();
-  else RemoveDoubleTracks();
+  // Keep only the best tracks if required
+  if (!GetRecoParam()->TrackAllTracks()) RemoveDoubleTracks();
+  else fRecTracksPtr->Compress();
   
   AliDebug(1,Form("Number of good candidates = %d",fNRecTracks));
   
+  return kTRUE;
+  
 }
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::MakeMoreTrackCandidates(AliMUONVClusterStore& clusterStore)
+Bool_t AliMUONTrackReconstructorK::MakeMoreTrackCandidates(AliMUONVClusterStore& clusterStore)
 {
-  /// To make extra track candidates (assuming linear propagation if the flag fgkMakeTrackCandidatesFast is set to kTRUE):
+  /// To make extra track candidates assuming linear propagation:
   /// clustering is supposed to be already done
   /// Start with segments made of 1 cluster in each of the stations 4 and 5 then follow track in remaining chambers.
-  /// Good candidates are made of at least three clusters if both station are requested (two otherwise).
+  /// Good candidates are made of at least three clusters if both stations are requested (two otherwise).
   /// Keep only best candidates or all of them according to the flag fgkTrackAllTracks.
   
   TClonesArray *segments;
+  AliMUONObjectPair *segment;
   AliMUONTrack *track;
   Int_t iCandidate = 0, iCurrentTrack, nCurrentTracks;
   Int_t initialNRecTracks = fNRecTracks;
@@ -190,19 +193,21 @@ void AliMUONTrackReconstructorK::MakeMoreTrackCandidates(AliMUONVClusterStore& c
       // Make segments between ch1 and ch2
       segments = MakeSegmentsBetweenChambers(clusterStore, ich1, ich2);
       
+      /// Remove segments already attached to a track
+      RemoveUsedSegments(*segments);
+      
       // Loop over segments
-      for (Int_t iseg=0; iseg<segments->GetEntriesFast(); iseg++) {
+      for (Int_t iSegment=0; iSegment<segments->GetEntriesFast(); iSegment++) {
        AliDebug(1,Form("Making primary candidate(1..) %d",++iCandidate));
+       segment = (AliMUONObjectPair*) segments->UncheckedAt(iSegment);
        
        // Transform segments to tracks and put them at the end of fRecTracksPtr
        iCurrentTrack = fRecTracksPtr->GetLast()+1;
-       track = new ((*fRecTracksPtr)[iCurrentTrack]) AliMUONTrack((AliMUONObjectPair*)((*segments)[iseg]),GetRecoParam()->GetBendingVertexDispersion());
+       track = new ((*fRecTracksPtr)[iCurrentTrack]) AliMUONTrack(segment,GetRecoParam()->GetBendingVertexDispersion());
        fNRecTracks++;
        
        // Look for compatible cluster(s) in the second chamber of station 5
-       if (GetRecoParam()->MakeTrackCandidatesFast())
-         clusterFound = FollowLinearTrackInChamber(*track, clusterStore, 17-ich2);
-       else clusterFound = FollowTrackInChamber(*track, clusterStore, 17-ich2);
+       clusterFound = FollowLinearTrackInChamber(*track, clusterStore, 17-ich2);
        
        // skip the original track in case it has been removed
        if (GetRecoParam()->TrackAllTracks() && clusterFound) iCurrentTrack++;
@@ -213,13 +218,18 @@ void AliMUONTrackReconstructorK::MakeMoreTrackCandidates(AliMUONVClusterStore& c
          track = (AliMUONTrack*) fRecTracksPtr->UncheckedAt(iCurrentTrack);
          
          // Look for compatible cluster(s) in the second chamber of station 4
-         if (GetRecoParam()->MakeTrackCandidatesFast())
-           FollowLinearTrackInChamber(*track, clusterStore, 13-ich1);
-         else FollowTrackInChamber(*track, clusterStore, 13-ich1);
+         FollowLinearTrackInChamber(*track, clusterStore, 13-ich1);
          
          iCurrentTrack++;
        }
        
+       // abort tracking if there are too many candidates
+       if ((fNRecTracks + segments->GetEntriesFast() - iSegment - 1) > GetRecoParam()->GetMaxTrackCandidates()) {
+         AliError(Form("Too many track candidates (%d tracks). Stop tracking.", fNRecTracks + segments->GetEntriesFast() - iSegment - 1));
+         delete segments;
+         return kFALSE;
+       }
+       
       }
       
       // delete the array of segments
@@ -227,41 +237,37 @@ void AliMUONTrackReconstructorK::MakeMoreTrackCandidates(AliMUONVClusterStore& c
     }
   }
   
-  fRecTracksPtr->Compress(); // this is essential before checking tracks
-  
-  // Retrace tracks using Kalman filter
-  for (Int_t iRecTrack = initialNRecTracks; iRecTrack < fNRecTracks; iRecTrack++) {
+  // Retrace tracks using Kalman filter (also compute track chi2) and select them
+  nCurrentTracks = fRecTracksPtr->GetLast()+1;
+  for (Int_t iRecTrack = initialNRecTracks; iRecTrack < nCurrentTracks; iRecTrack++) {
     track = (AliMUONTrack*) fRecTracksPtr->UncheckedAt(iRecTrack);
     
-    // Recompute track parameters and covariances using Kalman filter
-    RetraceTrack(*track,kTRUE);
+    // skip empty slots
+    if(!track) continue;
     
-    // Remove the track if the normalized chi2 is too high
-    // (only if the tracking has been done without magnetic field)
-    if (GetRecoParam()->MakeTrackCandidatesFast() &&
-       track->GetNormalizedChi2() > GetRecoParam()->GetSigmaCutForTracking() *
-                                    GetRecoParam()->GetSigmaCutForTracking()) {
+    // retrace tracks using Kalman filter and remove the ones for which extrap failed or that are out of limits
+    if (!RetraceTrack(*track,kTRUE) || !IsAcceptable(*((AliMUONTrackParam*)track->GetTrackParamAtCluster()->First()))) {
       fRecTracksPtr->Remove(track);
       fNRecTracks--;
     }
     
   }
   
-  // this is essential before checking tracks
-  if (GetRecoParam()->MakeTrackCandidatesFast()) fRecTracksPtr->Compress();
-  
-  // Keep all different tracks or only the best ones as required
-  if (GetRecoParam()->TrackAllTracks()) RemoveIdenticalTracks();
-  else RemoveDoubleTracks();
+  // Keep only the best tracks if required
+  if (!GetRecoParam()->TrackAllTracks()) RemoveDoubleTracks();
+  else fRecTracksPtr->Compress();
   
   AliDebug(1,Form("Number of good candidates = %d",fNRecTracks));
   
+  return kTRUE;
+  
 }
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::RetraceTrack(AliMUONTrack &trackCandidate, Bool_t resetSeed)
+Bool_t AliMUONTrackReconstructorK::RetraceTrack(AliMUONTrack &trackCandidate, Bool_t resetSeed)
 {
   /// Re-run the kalman filter from the most downstream cluster to the most uptream one
+  /// Return kFALSE in case of failure (i.e. extrapolation problem)
   AliDebug(1,"Enter RetraceTrack");
   
   AliMUONTrackParam* lastTrackParam = (AliMUONTrackParam*) trackCandidate.GetTrackParamAtCluster()->Last();
@@ -303,15 +309,26 @@ void AliMUONTrackReconstructorK::RetraceTrack(AliMUONTrack &trackCandidate, Bool
     lastParamCov.Zero();
     // Non bending plane
     lastParamCov(0,0) = cluster2->GetErrX2();
-    lastParamCov(1,1) = 100. * ( cluster1->GetErrX2() + cluster2->GetErrX2() ) / dZ / dZ;
+    lastParamCov(0,1) = - cluster2->GetErrX2() / dZ;
+    lastParamCov(1,0) = lastParamCov(0,1);
+    lastParamCov(1,1) = ( 1000. * cluster1->GetErrX2() + cluster2->GetErrX2() ) / dZ / dZ;
     // Bending plane
     lastParamCov(2,2) = cluster2->GetErrY2();
-    lastParamCov(3,3) = 100. * ( cluster1->GetErrY2() + cluster2->GetErrY2() ) / dZ / dZ;
+    lastParamCov(2,3) = - cluster2->GetErrY2() / dZ;
+    lastParamCov(3,2) = lastParamCov(2,3);
+    lastParamCov(3,3) = ( 1000. * cluster1->GetErrY2() + cluster2->GetErrY2() ) / dZ / dZ;
     // Inverse bending momentum (vertex resolution + bending slope resolution + 10% error on dipole parameters+field)
-    lastParamCov(4,4) = ((GetRecoParam()->GetBendingVertexDispersion() *
-                         GetRecoParam()->GetBendingVertexDispersion() +
-                         (z1 * z1 * cluster2->GetErrY2() + z2 * z2 * cluster1->GetErrY2()) / dZ / dZ) /
-                        bendingImpact / bendingImpact + 0.1 * 0.1) * inverseBendingMomentum * inverseBendingMomentum;
+    if (AliMUONTrackExtrap::IsFieldON()) {
+      lastParamCov(4,4) = ((GetRecoParam()->GetBendingVertexDispersion() *
+                           GetRecoParam()->GetBendingVertexDispersion() +
+                           (z1 * z1 * cluster2->GetErrY2() + z2 * z2 * 1000. * cluster1->GetErrY2()) / dZ / dZ) /
+                          bendingImpact / bendingImpact + 0.1 * 0.1) * inverseBendingMomentum * inverseBendingMomentum;
+      lastParamCov(2,4) = z1 * cluster2->GetErrY2() * inverseBendingMomentum / bendingImpact / dZ;
+      lastParamCov(4,2) = lastParamCov(2,4);
+      lastParamCov(3,4) = - (z1 * cluster2->GetErrY2() + z2 * 1000. * cluster1->GetErrY2()) *
+      inverseBendingMomentum / bendingImpact / dZ / dZ;
+      lastParamCov(4,3) = lastParamCov(3,4);
+    } else lastParamCov(4,4) = inverseBendingMomentum*inverseBendingMomentum;
     lastTrackParam->SetCovariances(lastParamCov);
     
     // Reset the track chi2
@@ -320,14 +337,15 @@ void AliMUONTrackReconstructorK::RetraceTrack(AliMUONTrack &trackCandidate, Bool
   }
   
   // Redo the tracking
-  RetracePartialTrack(trackCandidate, lastTrackParam);
+  return RetracePartialTrack(trackCandidate, lastTrackParam);
   
 }
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidate, const AliMUONTrackParam* startingTrackParam)
+Bool_t AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidate, const AliMUONTrackParam* startingTrackParam)
 {
   /// Re-run the kalman filter from the cluster attached to startingTrackParam to the most uptream cluster
+  /// Return kFALSE in case of failure (i.e. extrapolation problem)
   AliDebug(1,"Enter RetracePartialTrack");
   
   // Printout for debuging
@@ -339,6 +357,7 @@ void AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidat
   trackCandidate.SetGlobalChi2(startingTrackParam->GetTrackChi2());
   
   // loop over attached clusters until the first one and recompute track parameters and covariances using kalman filter
+  Bool_t extrapStatus = kTRUE;
   Int_t expectedChamber = startingTrackParam->GetClusterPtr()->GetChamberId() - 1;
   Int_t currentChamber;
   Double_t addChi2TrackAtCluster;
@@ -351,7 +370,7 @@ void AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidat
     trackParamAtCluster->SetCovariances(startingTrackParam->GetCovariances());
     
     // add MCS effect
-    AliMUONTrackExtrap::AddMCSEffect(trackParamAtCluster,AliMUONConstants::ChamberThicknessInX0(),1.);
+    AliMUONTrackExtrap::AddMCSEffect(trackParamAtCluster,AliMUONConstants::ChamberThicknessInX0(expectedChamber+1),-1.);
     
     // reset propagator for smoother
     if (GetRecoParam()->UseSmoother()) trackParamAtCluster->ResetPropagator();
@@ -360,16 +379,16 @@ void AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidat
     currentChamber = trackParamAtCluster->GetClusterPtr()->GetChamberId();
     while (currentChamber < expectedChamber) {
       // extrapolation to the missing chamber (update the propagator)
-      AliMUONTrackExtrap::ExtrapToZCov(trackParamAtCluster, AliMUONConstants::DefaultChamberZ(expectedChamber),
-                                      GetRecoParam()->UseSmoother());
+      if (!AliMUONTrackExtrap::ExtrapToZCov(trackParamAtCluster, AliMUONConstants::DefaultChamberZ(expectedChamber),
+                                           GetRecoParam()->UseSmoother())) extrapStatus = kFALSE;
       // add MCS effect
-      AliMUONTrackExtrap::AddMCSEffect(trackParamAtCluster,AliMUONConstants::ChamberThicknessInX0(),1.);
+      AliMUONTrackExtrap::AddMCSEffect(trackParamAtCluster,AliMUONConstants::ChamberThicknessInX0(expectedChamber),-1.);
       expectedChamber--;
     }
     
     // extrapolation to the plane of the cluster attached to the current trackParamAtCluster (update the propagator)
-    AliMUONTrackExtrap::ExtrapToZCov(trackParamAtCluster, trackParamAtCluster->GetClusterPtr()->GetZ(),
-                                    GetRecoParam()->UseSmoother());
+    if (!AliMUONTrackExtrap::ExtrapToZCov(trackParamAtCluster, trackParamAtCluster->GetClusterPtr()->GetZ(),
+                                         GetRecoParam()->UseSmoother())) extrapStatus = kFALSE;
     
     if (GetRecoParam()->UseSmoother()) {
       // save extrapolated parameters for smoother
@@ -397,10 +416,14 @@ void AliMUONTrackReconstructorK::RetracePartialTrack(AliMUONTrack &trackCandidat
     cout << "RetracePartialTrack: track chi2 after re-tracking: " << trackCandidate.GetGlobalChi2() << endl;
   }
   
+  // set global chi2 to max value in case of problem during track extrapolation
+  if (!extrapStatus) trackCandidate.SetGlobalChi2(2.*AliMUONTrack::MaxChi2());
+  return extrapStatus;
+  
 }
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::FollowTracks(AliMUONVClusterStore& clusterStore)
+Bool_t AliMUONTrackReconstructorK::FollowTracks(AliMUONVClusterStore& clusterStore)
 {
   /// Follow tracks in stations(1..) 3, 2 and 1
   AliDebug(1,"Enter FollowTracks");
@@ -448,6 +471,19 @@ void AliMUONTrackReconstructorK::FollowTracks(AliMUONVClusterStore& clusterStore
        
       }
       
+      // abort tracking if there are too many candidates
+      if (GetRecoParam()->RequestStation(station)) {
+       if (fNRecTracks > GetRecoParam()->GetMaxTrackCandidates()) {
+         AliError(Form("Too many track candidates (%d tracks). Stop tracking.", fNRecTracks));
+         return kFALSE;
+       }
+      } else {
+       if ((fNRecTracks + currentNRecTracks - iRecTrack - 1) > GetRecoParam()->GetMaxTrackCandidates()) {
+         AliError(Form("Too many track candidates (%d tracks). Stop tracking.", fNRecTracks + currentNRecTracks - iRecTrack - 1));
+         return kFALSE;
+       }
+      }
+      
     }
     
     fRecTracksPtr->Compress(); // this is essential before checking tracks
@@ -457,6 +493,8 @@ void AliMUONTrackReconstructorK::FollowTracks(AliMUONVClusterStore& clusterStore
     
   }
   
+  return kTRUE;
+  
 }
 
   //__________________________________________________________________________
@@ -471,12 +509,11 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInChamber(AliMUONTrack &trackCandi
   /// return kTRUE if new cluster(s) have been found (otherwise return kFALSE)
   AliDebug(1,Form("Enter FollowTrackInChamber(1..) %d", nextChamber+1));
   
-  Double_t bendingMomentum;
   Double_t chi2OfCluster;
   Double_t maxChi2OfCluster = 2. * GetRecoParam()->GetSigmaCutForTracking() *
                                   GetRecoParam()->GetSigmaCutForTracking(); // 2 because 2 quantities in chi2
   Double_t addChi2TrackAtCluster;
-  Double_t bestAddChi2TrackAtCluster = 1.e10;
+  Double_t bestAddChi2TrackAtCluster = AliMUONTrack::MaxChi2();
   Bool_t foundOneCluster = kFALSE;
   AliMUONTrack *newTrack = 0x0;
   AliMUONVCluster *cluster;
@@ -496,25 +533,25 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInChamber(AliMUONTrack &trackCandi
   }
   
   // Add MCS effect
-  AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(),1.);
+  Int_t currentChamber = extrapTrackParamAtCh.GetClusterPtr()->GetChamberId();
+  AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(currentChamber),-1.);
   
   // reset propagator for smoother
   if (GetRecoParam()->UseSmoother()) extrapTrackParamAtCh.ResetPropagator();
   
   // Add MCS in the missing chamber(s) if any
-  Int_t currentChamber = extrapTrackParamAtCh.GetClusterPtr()->GetChamberId();
   while (currentChamber > nextChamber + 1) {
     // extrapolation to the missing chamber
     currentChamber--;
-    AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
-                                    GetRecoParam()->UseSmoother());
+    if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
+                                         GetRecoParam()->UseSmoother())) return kFALSE;
     // add MCS effect
-    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(),1.);
+    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(currentChamber),-1.);
   }
   
   //Extrapolate trackCandidate to chamber
-  AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(nextChamber),
-                                  GetRecoParam()->UseSmoother());
+  if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(nextChamber),
+                                       GetRecoParam()->UseSmoother())) return kFALSE;
   
   // Printout for debuging
   if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 2) || (AliLog::GetGlobalDebugLevel() >= 2)) {
@@ -549,14 +586,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInChamber(AliMUONTrack &trackCandi
     
     // if good chi2 then consider to add cluster
     if (chi2OfCluster < maxChi2OfCluster) {
-      foundOneCluster = kTRUE;
-      
-      // Printout for debuging
-      if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
-       cout << "FollowTrackInChamber: found one cluster in chamber(1..): " << nextChamber+1
-       << " (Chi2 = " << chi2OfCluster << ")" << endl;
-       cluster->Print();
-      }
       
       if (GetRecoParam()->UseSmoother()) {
        // save extrapolated parameters for smoother
@@ -569,10 +598,18 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInChamber(AliMUONTrack &trackCandi
       // Compute new track parameters including new cluster using kalman filter
       addChi2TrackAtCluster = RunKalmanFilter(extrapTrackParamAtCluster);
       
-      // skip track with absolute bending momentum out of limits
-      bendingMomentum = TMath::Abs(1. / extrapTrackParamAtCluster.GetInverseBendingMomentum());
-      if (bendingMomentum < GetRecoParam()->GetMinBendingMomentum() ||
-         bendingMomentum > GetRecoParam()->GetMaxBendingMomentum()) continue;
+      // skip track out of limits
+      if (!IsAcceptable(extrapTrackParamAtCluster)) continue;
+      
+      // remember a cluster was found
+      foundOneCluster = kTRUE;
+      
+      // Printout for debuging
+      if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
+       cout << "FollowTrackInChamber: found one cluster in chamber(1..): " << nextChamber+1
+       << " (Chi2 = " << chi2OfCluster << ")" << endl;
+       cluster->Print();
+      }
       
       if (GetRecoParam()->TrackAllTracks()) {
        // copy trackCandidate into a new track put at the end of fRecTracksPtr and add the new cluster
@@ -645,14 +682,13 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     ch2 = 2*nextStation+1;
   }
   
-  Double_t bendingMomentum;
   Double_t chi2OfCluster;
   Double_t maxChi2OfCluster = 2. * GetRecoParam()->GetSigmaCutForTracking() *
                                   GetRecoParam()->GetSigmaCutForTracking(); // 2 because 2 quantities in chi2
   Double_t addChi2TrackAtCluster1;
   Double_t addChi2TrackAtCluster2;
-  Double_t bestAddChi2TrackAtCluster1 = 1.e10;
-  Double_t bestAddChi2TrackAtCluster2 = 1.e10;
+  Double_t bestAddChi2TrackAtCluster1 = AliMUONTrack::MaxChi2();
+  Double_t bestAddChi2TrackAtCluster2 = AliMUONTrack::MaxChi2();
   Bool_t foundOneCluster = kFALSE;
   Bool_t foundTwoClusters = kFALSE;
   AliMUONTrack *newTrack = 0x0;
@@ -664,13 +700,7 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
   AliMUONTrackParam bestTrackParamAtCluster1;
   AliMUONTrackParam bestTrackParamAtCluster2;
   
-  Int_t nClusters = clusterStore.GetSize();
-  Bool_t *clusterCh1Used = new Bool_t[nClusters];
-  for (Int_t i = 0; i < nClusters; i++) clusterCh1Used[i] = kFALSE;
-  Int_t iCluster1;
-  
   // Get track parameters according to the propagation direction
-  
   if (nextStation==4) extrapTrackParamAtCh = *(AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->Last();
   else extrapTrackParamAtCh = *(AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->First();
   
@@ -682,25 +712,25 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
   }
   
   // Add MCS effect
-  AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(),1.);
+  Int_t currentChamber = extrapTrackParamAtCh.GetClusterPtr()->GetChamberId();
+  AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(currentChamber),-1.);
   
   // reset propagator for smoother
   if (GetRecoParam()->UseSmoother()) extrapTrackParamAtCh.ResetPropagator();
   
   // Add MCS in the missing chamber(s) if any
-  Int_t currentChamber = extrapTrackParamAtCh.GetClusterPtr()->GetChamberId();
   while (ch1 < ch2 && currentChamber > ch2 + 1) {
     // extrapolation to the missing chamber
     currentChamber--;
-    AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
-                                    GetRecoParam()->UseSmoother());
+    if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(currentChamber),
+                                         GetRecoParam()->UseSmoother())) return kFALSE;
     // add MCS effect
-    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(),1.);
+    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(currentChamber),-1.);
   }
   
   //Extrapolate trackCandidate to chamber "ch2"
-  AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(ch2),
-                                  GetRecoParam()->UseSmoother());
+  if (!AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(ch2),
+                                       GetRecoParam()->UseSmoother())) return kFALSE;
   
   // Printout for debuging
   if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 2) || (AliLog::GetGlobalDebugLevel() >= 2)) {
@@ -720,6 +750,11 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     if (nextStation < 3) AskForNewClustersInStation(extrapTrackParamAtCh, clusterStore, nextStation);
   }
   
+  Int_t nClusters = clusterStore.GetSize();
+  Bool_t *clusterCh1Used = new Bool_t[nClusters];
+  for (Int_t i = 0; i < nClusters; i++) clusterCh1Used[i] = kFALSE;
+  Int_t iCluster1;
+  
   // Create iterators to loop over clusters in both chambers
   TIter nextInCh1(clusterStore.CreateChamberIterator(ch1,ch1));
   TIter nextInCh2(clusterStore.CreateChamberIterator(ch2,ch2));
@@ -736,15 +771,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     
     // if good chi2 then try to attach a cluster in the other chamber too
     if (chi2OfCluster < maxChi2OfCluster) {
-      Bool_t foundSecondCluster = kFALSE;
-      
-      // Printout for debuging
-      if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
-        cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch2+1
-            << " (Chi2 = " << chi2OfCluster << ")" << endl;
-       clusterCh2->Print();
-        cout << "                      look for second clusters in chamber(1..): " << ch1+1 << " ..." << endl;
-      }
       
       if (GetRecoParam()->UseSmoother()) {
         // save extrapolated parameters for smoother
@@ -757,30 +783,37 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
       // Compute new track parameters including "clusterCh2" using kalman filter
       addChi2TrackAtCluster2 = RunKalmanFilter(extrapTrackParamAtCluster2);
       
-      // skip track with absolute bending momentum out of limits
-      bendingMomentum = TMath::Abs(1. / extrapTrackParamAtCluster2.GetInverseBendingMomentum());
-      if (bendingMomentum < GetRecoParam()->GetMinBendingMomentum() ||
-         bendingMomentum > GetRecoParam()->GetMaxBendingMomentum()) continue;
-       
+      // skip track out of limits
+      if (!IsAcceptable(extrapTrackParamAtCluster2)) continue;
+      
+      // Printout for debuging
+      if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
+        cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch2+1
+       << " (Chi2 = " << chi2OfCluster << ")" << endl;
+       clusterCh2->Print();
+        cout << "                      look for second clusters in chamber(1..): " << ch1+1 << " ..." << endl;
+      }
+      
       // copy new track parameters for next step
       extrapTrackParam = extrapTrackParamAtCluster2;
       
       // add MCS effect
-      AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParam,AliMUONConstants::ChamberThicknessInX0(),1.);
+      AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParam,AliMUONConstants::ChamberThicknessInX0(ch2),-1.);
       
       // reset propagator for smoother
       if (GetRecoParam()->UseSmoother()) extrapTrackParam.ResetPropagator();
       
       //Extrapolate track parameters to chamber "ch1"
-      AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParam, AliMUONConstants::DefaultChamberZ(ch1),
-                                      GetRecoParam()->UseSmoother());
+      Bool_t normalExtrap = AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParam, AliMUONConstants::DefaultChamberZ(ch1),
+                                                            GetRecoParam()->UseSmoother());
       
       // reset cluster iterator of chamber 1
       nextInCh1.Reset();
       iCluster1 = -1;
       
       // look for second candidates in chamber 1
-      while ( ( clusterCh1 = static_cast<AliMUONVCluster*>(nextInCh1()) ) ) {
+      Bool_t foundSecondCluster = kFALSE;
+      if (normalExtrap) while ( ( clusterCh1 = static_cast<AliMUONVCluster*>(nextInCh1()) ) ) {
        iCluster1++;
        
        // try to add the current cluster fast
@@ -792,15 +825,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
        
        // if good chi2 then consider to add the 2 clusters to the "trackCandidate"
        if (chi2OfCluster < maxChi2OfCluster) {
-         foundSecondCluster = kTRUE;
-         foundTwoClusters = kTRUE;
-          
-         // Printout for debuging
-         if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
-           cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch1+1
-                << " (Chi2 = " << chi2OfCluster << ")" << endl;
-           clusterCh1->Print();
-         }
           
           if (GetRecoParam()->UseSmoother()) {
             // save extrapolated parameters for smoother
@@ -813,10 +837,19 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
           // Compute new track parameters including "clusterCh1" using kalman filter
           addChi2TrackAtCluster1 = RunKalmanFilter(extrapTrackParamAtCluster1);
           
-         // skip track with absolute bending momentum out of limits
-         bendingMomentum = TMath::Abs(1. / extrapTrackParamAtCluster1.GetInverseBendingMomentum());
-         if (bendingMomentum < GetRecoParam()->GetMinBendingMomentum() ||
-             bendingMomentum > GetRecoParam()->GetMaxBendingMomentum()) continue;
+         // skip track out of limits
+         if (!IsAcceptable(extrapTrackParamAtCluster1)) continue;
+         
+         // remember a second cluster was found
+         foundSecondCluster = kTRUE;
+         foundTwoClusters = kTRUE;
+          
+         // Printout for debuging
+         if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
+           cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch1+1
+           << " (Chi2 = " << chi2OfCluster << ")" << endl;
+           clusterCh1->Print();
+         }
          
          if (GetRecoParam()->TrackAllTracks()) {
            // copy trackCandidate into a new track put at the end of fRecTracksPtr and add the new clusters
@@ -824,10 +857,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
            UpdateTrack(*newTrack,extrapTrackParamAtCluster1,extrapTrackParamAtCluster2,addChi2TrackAtCluster1,addChi2TrackAtCluster2);
            fNRecTracks++;
            
-           // if we are arrived on station(1..) 5, recompute track parameters and covariances starting from this station
-           // (going in the right direction)
-           if (nextStation == 4) RetraceTrack(*newTrack,kTRUE);
-           
            // Tag clusterCh1 as used
            clusterCh1Used[iCluster1] = kTRUE;
            
@@ -851,6 +880,8 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
       
       // if no clusterCh1 found then consider to add clusterCh2 only
       if (!foundSecondCluster) {
+       
+       // remember a cluster was found
        foundOneCluster = kTRUE;
         
        if (GetRecoParam()->TrackAllTracks()) {
@@ -859,10 +890,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
          UpdateTrack(*newTrack,extrapTrackParamAtCluster2,addChi2TrackAtCluster2);
          fNRecTracks++;
          
-         // if we are arrived on station(1..) 5, recompute track parameters and covariances starting from this station
-         // (going in the right direction)
-         if (nextStation == 4) RetraceTrack(*newTrack,kTRUE);
-         
          // Printout for debuging
          if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
            cout << "FollowTrackInStation: added one cluster in chamber(1..): " << ch2+1 << endl;
@@ -886,11 +913,11 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
   if (GetRecoParam()->TrackAllTracks() || !foundTwoClusters) {
     
     // add MCS effect for next step
-    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(),1.);
+    AliMUONTrackExtrap::AddMCSEffect(&extrapTrackParamAtCh,AliMUONConstants::ChamberThicknessInX0(ch2),-1.);
     
     //Extrapolate trackCandidate to chamber "ch1"
-    AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(ch1),
-                                    GetRecoParam()->UseSmoother());
+    Bool_t normalExtrap = AliMUONTrackExtrap::ExtrapToZCov(&extrapTrackParamAtCh, AliMUONConstants::DefaultChamberZ(ch1),
+                                                          GetRecoParam()->UseSmoother());
     
     // Printout for debuging
     if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 2) || (AliLog::GetGlobalDebugLevel() >= 2)) {
@@ -909,7 +936,7 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     iCluster1 = -1;
     
     // look for second candidates in chamber 1
-    while ( ( clusterCh1 = static_cast<AliMUONVCluster*>(nextInCh1()) ) ) {
+    if (normalExtrap) while ( ( clusterCh1 = static_cast<AliMUONVCluster*>(nextInCh1()) ) ) {
       iCluster1++;
       
       if (clusterCh1Used[iCluster1]) continue; // Skip clusters already used
@@ -924,14 +951,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
       // if good chi2 then consider to add clusterCh1
       // We do not try to attach a cluster in the other chamber too since it has already been done above
       if (chi2OfCluster < maxChi2OfCluster) {
-       foundOneCluster = kTRUE;
-       
-       // Printout for debuging
-       if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
-         cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch1+1
-              << " (Chi2 = " << chi2OfCluster << ")" << endl;
-         clusterCh1->Print();
-       }
         
        if (GetRecoParam()->UseSmoother()) {
           // save extrapolated parameters for smoother
@@ -944,10 +963,18 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
         // Compute new track parameters including "clusterCh1" using kalman filter
         addChi2TrackAtCluster1 = RunKalmanFilter(extrapTrackParamAtCluster1);
         
-       // skip track with absolute bending momentum out of limits
-       bendingMomentum = TMath::Abs(1. / extrapTrackParamAtCluster1.GetInverseBendingMomentum());
-       if (bendingMomentum < GetRecoParam()->GetMinBendingMomentum() ||
-           bendingMomentum > GetRecoParam()->GetMaxBendingMomentum()) continue;
+       // skip track out of limits
+       if (!IsAcceptable(extrapTrackParamAtCluster1)) continue;
+       
+       // remember a cluster was found
+       foundOneCluster = kTRUE;
+       
+       // Printout for debuging
+       if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
+         cout << "FollowTrackInStation: found one cluster in chamber(1..): " << ch1+1
+         << " (Chi2 = " << chi2OfCluster << ")" << endl;
+         clusterCh1->Print();
+       }
        
        if (GetRecoParam()->TrackAllTracks()) {
          // copy trackCandidate into a new track put at the end of fRecTracksPtr and add the new cluster
@@ -955,10 +982,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
          UpdateTrack(*newTrack,extrapTrackParamAtCluster1,addChi2TrackAtCluster1);
          fNRecTracks++;
          
-         // if we are arrived on station(1..) 5, recompute track parameters and covariances starting from this station
-         // (going in the right direction)
-         if (nextStation == 4) RetraceTrack(*newTrack,kTRUE);
-         
          // Printout for debuging
          if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
            cout << "FollowTrackInStation: added one cluster in chamber(1..): " << ch1+1 << endl;
@@ -982,10 +1005,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     if (foundTwoClusters) {
       UpdateTrack(trackCandidate,bestTrackParamAtCluster1,bestTrackParamAtCluster2,bestAddChi2TrackAtCluster1,bestAddChi2TrackAtCluster2);
       
-      // if we are arrived on station(1..) 5, recompute track parameters and covariances starting from this station
-      // (going in the right direction)
-      if (nextStation == 4) RetraceTrack(trackCandidate,kTRUE);
-      
       // Printout for debuging
       if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
         cout << "FollowTrackInStation: added the two best clusters in station(1..): " << nextStation+1 << endl;
@@ -995,10 +1014,6 @@ Bool_t AliMUONTrackReconstructorK::FollowTrackInStation(AliMUONTrack &trackCandi
     } else if (foundOneCluster) {
       UpdateTrack(trackCandidate,bestTrackParamAtCluster1,bestAddChi2TrackAtCluster1);
       
-      // if we are arrived on station(1..) 5, recompute track parameters and covariances starting from this station
-      // (going in the right direction)
-      if (nextStation == 4) RetraceTrack(trackCandidate,kTRUE);
-      
       // Printout for debuging
       if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
         cout << "FollowTrackInStation: added the best cluster in chamber(1..): " << bestTrackParamAtCluster1.GetClusterPtr()->GetChamberId()+1 << endl;
@@ -1049,7 +1064,7 @@ Double_t AliMUONTrackReconstructorK::RunKalmanFilter(AliMUONTrackParam &trackPar
     paramWeight.Invert();
   } else {
     AliWarning(" Determinant = 0");
-    return 1.e10;
+    return 2.*AliMUONTrack::MaxChi2();
   }
   
   // Compute the new cluster weight (U)
@@ -1064,7 +1079,7 @@ Double_t AliMUONTrackReconstructorK::RunKalmanFilter(AliMUONTrackParam &trackPar
     newParamCov.Invert();
   } else {
     AliWarning(" Determinant = 0");
-    return 1.e10;
+    return 2.*AliMUONTrack::MaxChi2();
   }
   
   // Save the new parameters covariance matrix
@@ -1204,12 +1219,10 @@ Bool_t AliMUONTrackReconstructorK::RecoverTrack(AliMUONTrack &trackCandidate, Al
   trackCandidate.RemoveTrackParamAtCluster((AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->UncheckedAt(worstClusterNumber));
   
   // Re-calculate track parameters at the (new) first cluster
-  RetracePartialTrack(trackCandidate,(AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->UncheckedAt(1));
+  if (!RetracePartialTrack(trackCandidate,(AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->UncheckedAt(1))) return kFALSE;
   
-  // skip track with absolute bending momentum out of limits
-  Double_t bendingMomentum = TMath::Abs(1. / ((AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->First())->GetInverseBendingMomentum());
-  if (bendingMomentum < GetRecoParam()->GetMinBendingMomentum() ||
-      bendingMomentum > GetRecoParam()->GetMaxBendingMomentum()) return kFALSE;
+  // skip track out of limits
+  if (!IsAcceptable(*((AliMUONTrackParam*)trackCandidate.GetTrackParamAtCluster()->First()))) return kFALSE;
   
   // Look for new cluster(s) in next station
   return FollowTrackInStation(trackCandidate, clusterStore, nextStation);
@@ -1227,17 +1240,20 @@ Bool_t AliMUONTrackReconstructorK::RunSmoother(AliMUONTrack &track)
   // Smoothed parameters and covariances at first cluster = filtered parameters and covariances
   previousTrackParam->SetSmoothParameters(previousTrackParam->GetParameters());
   previousTrackParam->SetSmoothCovariances(previousTrackParam->GetCovariances());
+
+  AliMUONTrackParam *currentTrackParam = (AliMUONTrackParam*) track.GetTrackParamAtCluster()->After(previousTrackParam);
   
-  // Compute local chi2 at first cluster
-  AliMUONVCluster *cluster = previousTrackParam->GetClusterPtr();
-  Double_t dX = cluster->GetX() - previousTrackParam->GetNonBendingCoor();
-  Double_t dY = cluster->GetY() - previousTrackParam->GetBendingCoor();
-  Double_t chi2 = dX * dX / cluster->GetErrX2() + dY * dY / cluster->GetErrY2();
+  // Save local chi2 at first cluster = last additional chi2 provided by Kalman
+  previousTrackParam->SetLocalChi2(previousTrackParam->GetTrackChi2() - currentTrackParam->GetTrackChi2());
   
-  // Save local chi2 at first cluster
-  previousTrackParam->SetLocalChi2(chi2);
+  // if the track contains only 2 clusters simply copy the filtered parameters
+  if (track.GetNClusters() == 2) {
+    currentTrackParam->SetSmoothParameters(currentTrackParam->GetParameters());
+    currentTrackParam->SetSmoothCovariances(currentTrackParam->GetCovariances());
+    currentTrackParam->SetLocalChi2(currentTrackParam->GetTrackChi2());
+    return kTRUE;
+  }
   
-  AliMUONTrackParam *currentTrackParam = (AliMUONTrackParam*) track.GetTrackParamAtCluster()->After(previousTrackParam);
   while (currentTrackParam) {
     
     // Get variables
@@ -1249,7 +1265,7 @@ Bool_t AliMUONTrackReconstructorK::RunSmoother(AliMUONTrack &track)
     const TMatrixD &filteredCovariances       = currentTrackParam->GetCovariances();        // C(k k)
     const TMatrixD &previousSmoothCovariances = previousTrackParam->GetSmoothCovariances(); // C(k+1 n)
     
-    // Compute smoother gain: A(k) = C(kk) * F(f)^t * (C(k+1 k))^-1
+    // Compute smoother gain: A(k) = C(kk) * F(k)^t * (C(k+1 k))^-1
     TMatrixD extrapWeight(extrapCovariances);
     if (extrapWeight.Determinant() != 0) {
       extrapWeight.Invert(); // (C(k+1 k))^-1
@@ -1257,8 +1273,8 @@ Bool_t AliMUONTrackReconstructorK::RunSmoother(AliMUONTrack &track)
       AliWarning(" Determinant = 0");
       return kFALSE;
     }
-    TMatrixD smootherGain(filteredCovariances,TMatrixD::kMultTranspose,propagator); // C(kk) * F(f)^t
-    smootherGain *= extrapWeight; // C(kk) * F(f)^t * (C(k+1 k))^-1
+    TMatrixD smootherGain(filteredCovariances,TMatrixD::kMultTranspose,propagator); // C(kk) * F(k)^t
+    smootherGain *= extrapWeight; // C(kk) * F(k)^t * (C(k+1 k))^-1
     
     // Compute smoothed parameters: X(k n) = X(k k) + A(k) * (X(k+1 n) - X(k+1 k))
     TMatrixD tmpParam(previousSmoothParameters,TMatrixD::kMinus,extrapParameters); // X(k+1 n) - X(k+1 k)
@@ -1278,7 +1294,7 @@ Bool_t AliMUONTrackReconstructorK::RunSmoother(AliMUONTrack &track)
     currentTrackParam->SetSmoothCovariances(smoothCovariances);
     
     // Compute smoothed residual: r(k n) = cluster - X(k n)
-    cluster = currentTrackParam->GetClusterPtr();
+    AliMUONVCluster* cluster = currentTrackParam->GetClusterPtr();
     TMatrixD smoothResidual(2,1);
     smoothResidual.Zero();
     smoothResidual(0,0) = cluster->GetX() - smoothParameters(0,0);
@@ -1313,20 +1329,23 @@ Bool_t AliMUONTrackReconstructorK::RunSmoother(AliMUONTrack &track)
 }
 
   //__________________________________________________________________________
-void AliMUONTrackReconstructorK::ComplementTracks(const AliMUONVClusterStore& clusterStore)
+Bool_t AliMUONTrackReconstructorK::ComplementTracks(const AliMUONVClusterStore& clusterStore)
 {
   /// Complete tracks by adding missing clusters (if there is an overlap between
-  /// two detection elements, the track may have two clusters in the same chamber)
-  /// Recompute track parameters and covariances at each clusters
+  /// two detection elements, the track may have two clusters in the same chamber).
+  /// Recompute track parameters and covariances at each clusters.
+  /// Remove tracks getting abnormal (i.e. extrapolation failed...) after being complemented.
+  /// Return kTRUE if one or more tracks have been complemented or removed.
   AliDebug(1,"Enter ComplementTracks");
   
   Int_t chamberId, detElemId;
   Double_t chi2OfCluster, addChi2TrackAtCluster, bestAddChi2TrackAtCluster;
   Double_t maxChi2OfCluster = 2. * GetRecoParam()->GetSigmaCutForTracking() *
                                   GetRecoParam()->GetSigmaCutForTracking(); // 2 because 2 quantities in chi2
-  Bool_t foundOneCluster, trackModified;
+  Bool_t foundOneCluster, trackModified, hasChanged = kFALSE;
   AliMUONVCluster *cluster;
   AliMUONTrackParam *trackParam, *previousTrackParam, *nextTrackParam, trackParamAtCluster, bestTrackParamAtCluster;
+  AliMUONTrack *nextTrack;
   
   AliMUONTrack *track = (AliMUONTrack*) fRecTracksPtr->First();
   while (track) {
@@ -1336,7 +1355,7 @@ void AliMUONTrackReconstructorK::ComplementTracks(const AliMUONVClusterStore& cl
     previousTrackParam = trackParam;
     while (trackParam) {
       foundOneCluster = kFALSE;
-      bestAddChi2TrackAtCluster = 1.e10;
+      bestAddChi2TrackAtCluster = AliMUONTrack::MaxChi2();
       chamberId = trackParam->GetClusterPtr()->GetChamberId();
       detElemId = trackParam->GetClusterPtr()->GetDetElemId();
       
@@ -1395,18 +1414,28 @@ void AliMUONTrackReconstructorK::ComplementTracks(const AliMUONVClusterStore& cl
        bestTrackParamAtCluster.SetRemovable(kTRUE);
        track->AddTrackParamAtCluster(bestTrackParamAtCluster,*(bestTrackParamAtCluster.GetClusterPtr()));
        trackModified = kTRUE;
+       hasChanged = kTRUE;
       }
       
       previousTrackParam = trackParam;
       trackParam = nextTrackParam;
     }
     
+    // prepare next track
+    nextTrack = (AliMUONTrack*) fRecTracksPtr->After(track);
+    
     // re-compute track parameters using kalman filter if needed
-    if (trackModified) RetraceTrack(*track,kTRUE);
+    if (trackModified && !RetraceTrack(*track,kTRUE)) {
+      AliWarning("track modified but problem occur during refitting --> remove track");
+      fRecTracksPtr->Remove(track);
+      fNRecTracks--;
+    }
     
-    track = (AliMUONTrack*) fRecTracksPtr->After(track);
+    track = nextTrack;
   }
   
+  return hasChanged;
+  
 }
 
 //__________________________________________________________________________
@@ -1415,10 +1444,12 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
   /// Improve the given track by removing removable clusters with local chi2 highter than the defined cut
   /// Removable clusters are identified by the method AliMUONTrack::TagRemovableClusters()
   /// Recompute track parameters and covariances at the remaining clusters
+  /// and if something goes wrong (i.e. extrapolation failed...) set track chi2 to max value
   AliDebug(1,"Enter ImproveTrack");
   
   Double_t localChi2, worstLocalChi2;
-  AliMUONTrackParam *trackParamAtCluster, *worstTrackParamAtCluster, *nextTrackParam;
+  AliMUONTrackParam *trackParamAtCluster, *worstTrackParamAtCluster, *nextTrackParam, *next2nextTrackParam;
+  Int_t nextChamber, next2nextChamber;
   Bool_t smoothed;
   Double_t sigmaCut2 = GetRecoParam()->GetSigmaCutForImprovement() *
                        GetRecoParam()->GetSigmaCutForImprovement();
@@ -1436,7 +1467,12 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
     if (!smoothed) {
       
       // Update track parameters and covariances
-      track.UpdateCovTrackParamAtCluster();
+      if (!track.UpdateCovTrackParamAtCluster()) {
+       AliWarning("unable to update track parameters and covariances --> stop improvement");
+       // restore the kalman parameters
+       RetraceTrack(track,kTRUE);
+       break;
+      }
       
       // Compute local chi2 of each clusters
       track.ComputeLocalChi2(kTRUE);
@@ -1444,7 +1480,7 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
     
     // Look for the cluster to remove
     worstTrackParamAtCluster = 0x0;
-    worstLocalChi2 = 0.;
+    worstLocalChi2 = -1.;
     trackParamAtCluster = (AliMUONTrackParam*)track.GetTrackParamAtCluster()->First();
     while (trackParamAtCluster) {
       
@@ -1464,12 +1500,6 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
       trackParamAtCluster = (AliMUONTrackParam*)track.GetTrackParamAtCluster()->After(trackParamAtCluster);
     }
     
-    // Check if worst cluster found
-    if (!worstTrackParamAtCluster) {
-      AliWarning("Bad local chi2 values?");
-      break;
-    }
-    
     // Check whether the worst chi2 is under requirement or not
     if (worstLocalChi2 < 2. * sigmaCut2) { // 2 because 2 quantities in chi2
       track.SetImproved(kTRUE);
@@ -1477,7 +1507,11 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
     }
     
     // if the worst cluster is not removable then stop improvement
-    if (!worstTrackParamAtCluster->IsRemovable()) break;
+    if (!worstTrackParamAtCluster->IsRemovable()) {
+      // restore the kalman parameters in case they have been lost
+      if (!smoothed) RetraceTrack(track,kTRUE);
+      break;
+    }
     
     // get track parameters at cluster next to the one to be removed
     nextTrackParam = (AliMUONTrackParam*) track.GetTrackParamAtCluster()->After(worstTrackParamAtCluster);
@@ -1488,9 +1522,29 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
     // Re-calculate track parameters
     // - from the cluster immediately downstream the one suppressed
     // - or from the begining - if parameters have been re-computed using the standard method (kalman parameters have been lost)
-    //                 - or if the removed cluster was the last one
-    if (smoothed && nextTrackParam) RetracePartialTrack(track,nextTrackParam);
-    else RetraceTrack(track,kTRUE);
+    //                        - or if the removed cluster was used to compute the tracking seed
+    Bool_t normalExtrap;
+    if (smoothed && nextTrackParam) {
+      
+      nextChamber = nextTrackParam->GetClusterPtr()->GetChamberId();
+      next2nextTrackParam = nextTrackParam;
+      do {
+       
+       next2nextChamber = next2nextTrackParam->GetClusterPtr()->GetChamberId();
+       next2nextTrackParam = (AliMUONTrackParam*) track.GetTrackParamAtCluster()->After(next2nextTrackParam);
+       
+      } while (next2nextTrackParam && (next2nextChamber == nextChamber));
+      
+      if (next2nextChamber == nextChamber) normalExtrap = RetraceTrack(track,kTRUE);
+      else normalExtrap = RetracePartialTrack(track,nextTrackParam);
+      
+    } else normalExtrap = RetraceTrack(track,kTRUE);
+    
+    // stop in case of extrapolation problem
+    if (!normalExtrap) {
+      AliWarning("track partially improved but problem occur during refitting --> stop improvement");
+      break;
+    }
     
     // Printout for debuging
     if ((AliLog::GetDebugLevel("MUON","AliMUONTrackReconstructorK") >= 1) || (AliLog::GetGlobalDebugLevel() >= 1)) {
@@ -1502,20 +1556,27 @@ void AliMUONTrackReconstructorK::ImproveTrack(AliMUONTrack &track)
 }
 
 //__________________________________________________________________________
-void AliMUONTrackReconstructorK::FinalizeTrack(AliMUONTrack &track)
+Bool_t AliMUONTrackReconstructorK::FinalizeTrack(AliMUONTrack &track)
 {
   /// Update track parameters and covariances at each attached cluster
   /// using smoother if required, if not already done
+  /// return kFALSE if the track cannot be extrapolated uo to the last chamber
   
   AliMUONTrackParam *trackParamAtCluster;
   Bool_t smoothed = kFALSE;
   
   // update track parameters (using smoother if required) if not already done
-  if (!track.IsImproved()) {
-    smoothed = kFALSE;
+  if (track.IsImproved()) smoothed = GetRecoParam()->UseSmoother();
+  else {
     if (GetRecoParam()->UseSmoother()) smoothed = RunSmoother(track);
-    if (!smoothed) track.UpdateCovTrackParamAtCluster();
-  } else smoothed = GetRecoParam()->UseSmoother();
+    if (!smoothed) {
+      if (track.UpdateCovTrackParamAtCluster()) track.ComputeLocalChi2(kTRUE);
+      else {
+       AliWarning("finalization failed due to extrapolation problem");
+       return kFALSE;
+      }
+    }
+  }
   
   // copy smoothed parameters and covariances if any
   if (smoothed) {
@@ -1531,30 +1592,38 @@ void AliMUONTrackReconstructorK::FinalizeTrack(AliMUONTrack &track)
     
   }
   
+  return kTRUE;
+  
 }
 
   //__________________________________________________________________________
 Bool_t AliMUONTrackReconstructorK::RefitTrack(AliMUONTrack &track, Bool_t enableImprovement)
 {
   /// re-fit the given track
+  AliDebug(1,"Enter RefitTrack");
   
-  // check validity of the track
-  if (track.GetNClusters() < 3) {
-    AliWarning("the track does not contain enough clusters --> unable to refit");
+  // check validity of the track (i.e. at least 2 chambers hit on stations 4 and 5)
+  if (!track.IsValid(0)) {
+    AliWarning("the track is not valid --> unable to refit");
     return kFALSE;
   }
   
   // re-compute track parameters and covariances using Kalman filter
-  RetraceTrack(track,kTRUE);
+  if (!RetraceTrack(track,kTRUE)) {
+    AliWarning("bad track refitting due to extrapolation failure");
+    return kFALSE;
+  }
   
   // Improve the reconstructed tracks if required
   track.SetImproved(kFALSE);
   if (enableImprovement && GetRecoParam()->ImproveTracks()) ImproveTrack(track);
   
   // Fill AliMUONTrack data members
-  FinalizeTrack(track);
-  
-  return kTRUE;
+  if (track.GetGlobalChi2() < AliMUONTrack::MaxChi2()) return FinalizeTrack(track);
+  else {
+    AliWarning("track not finalized due to extrapolation failure");
+    return kFALSE;
+  }
   
 }