X-Git-Url: http://git.uio.no/git/?a=blobdiff_plain;f=MUON%2FAliMUONClusterSplitterMLEM.cxx;h=b2efc607a84c5b899182afacca0e539811b418b1;hb=dba333aea1f30dee5c9f8af2b879baef7b8d9dba;hp=acc31137566d2b9bd089460e984c7332e7771fe0;hpb=3d1463c8f7148e36069c24f20cde34e096d5d6a9;p=u%2Fmrichter%2FAliRoot.git

diff --git a/MUON/AliMUONClusterSplitterMLEM.cxx b/MUON/AliMUONClusterSplitterMLEM.cxx
index acc31137566..b2efc607a84 100644
--- a/MUON/AliMUONClusterSplitterMLEM.cxx
+++ b/MUON/AliMUONClusterSplitterMLEM.cxx
@@ -13,29 +13,31 @@
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/
 
-// $Id$
+/* $Id$ */
 
 //-----------------------------------------------------------------------------
 /// \class AliMUONClusterSplitterMLEM
 /// 
-/// Splitter class for the MLEM algorithm...
-///
-/// FIXME: describe it a little bit more here...
+/// Splitter class for the MLEM algorithm. Performs fitting procedure
+/// with up to 3 hit candidates and tries to split clusters if the number
+/// of candidates exceeds 3.
 ///
 /// \author Laurent Aphecetche (for the "new" C++ structure) and 
 /// Alexander Zinchenko, JINR Dubna, for the hardcore of it ;-)
 //-----------------------------------------------------------------------------
 
 #include "AliMUONClusterSplitterMLEM.h"
+#include "AliMUONClusterFinderMLEM.h" // for status flag constants
 
 #include "AliMUONCluster.h"
 #include "AliMUONPad.h"
 #include "AliMUONPad.h"
-#include "AliMpStationType.h"
 #include "AliMUONConstants.h"
 #include "AliMpDEManager.h"
 #include "AliMUONMathieson.h"
 
+#include "AliMpEncodePair.h"
+
 #include "AliLog.h"
 
 #include <TClonesArray.h>
@@ -43,7 +45,6 @@
 #include <TMath.h>
 #include <TMatrixD.h>
 #include <TObjArray.h>
-#include <TROOT.h>
 #include <TRandom.h>
 #include <Riostream.h>
 
@@ -51,13 +52,14 @@
 ClassImp(AliMUONClusterSplitterMLEM)
 /// \endcond
 
-const Double_t AliMUONClusterSplitterMLEM::fgkCouplMin = 1.e-3; // threshold on coupling 
+//const Double_t AliMUONClusterSplitterMLEM::fgkCouplMin = 1.e-3; // threshold on coupling 
+const Double_t AliMUONClusterSplitterMLEM::fgkCouplMin = 1.e-2; // threshold on coupling 
 
 //_____________________________________________________________________________
 AliMUONClusterSplitterMLEM::AliMUONClusterSplitterMLEM(Int_t detElemId, 
-                                                       TObjArray* fPixArray) 
+                                                       TObjArray* pixArray) 
 : TObject(),
-fPixArray(fPixArray),
+fPixArray(pixArray),
 fMathieson(0x0),
 fDetElemId(detElemId),
 fNpar(0),
@@ -67,13 +69,13 @@ fDebug(0)
 {
   /// Constructor
   
-  AliMp::StationType stationType = AliMpDEManager::GetStationType(fDetElemId);
+  AliMq::Station12Type stationType = AliMpDEManager::GetStation12Type(fDetElemId);
   
   Float_t kx3 = AliMUONConstants::SqrtKx3();
   Float_t ky3 = AliMUONConstants::SqrtKy3();
   Float_t pitch = AliMUONConstants::Pitch();
   
-  if ( stationType == AliMp::kStation1 )
+  if ( stationType == AliMq::kStation1 )
   {
     kx3 = AliMUONConstants::SqrtKx3St1();
     ky3 = AliMUONConstants::SqrtKy3St1();
@@ -109,8 +111,9 @@ AliMUONClusterSplitterMLEM::AddBin(TH2 *mlem,
   Double_t cont1, cont = mlem->GetCellContent(jc,ic);
   AliMUONPad *pixPtr = 0;
   
-  for (Int_t i=TMath::Max(ic-1,1); i<=TMath::Min(ic+1,ny); i++) {
-    for (Int_t j=TMath::Max(jc-1,1); j<=TMath::Min(jc+1,nx); j++) {
+  Int_t ie = TMath::Min(ic+1,ny), je = TMath::Min(jc+1,nx);
+  for (Int_t i = TMath::Max(ic-1,1); i <= ie; ++i) {
+    for (Int_t j = TMath::Max(jc-1,1); j <= je; ++j) {
       if (i != ic && j != jc) continue;
       if (used[(i-1)*nx+j-1]) continue;
       cont1 = mlem->GetCellContent(j,i);
@@ -120,8 +123,8 @@ AliMUONClusterSplitterMLEM::AddBin(TH2 *mlem,
       if (pix) pix->Add(BinToPix(mlem,j,i)); 
       else {
         pixPtr = new AliMUONPad (mlem->GetXaxis()->GetBinCenter(j), 
-                                   mlem->GetYaxis()->GetBinCenter(i), 0, 0, cont1);
-        fPixArray->Add((TObject*)pixPtr);
+				 mlem->GetYaxis()->GetBinCenter(i), 0, 0, cont1);
+        fPixArray->Add(pixPtr);
       }
       AddBin(mlem, i, j, mode, used, pix); // recursive call
     }
@@ -136,7 +139,7 @@ AliMUONClusterSplitterMLEM::AddCluster(Int_t ic, Int_t nclust,
 {
   /// Add a cluster to the group of coupled clusters
   
-  for (Int_t i=0; i<nclust; i++) {
+  for (Int_t i = 0; i < nclust; ++i) {
     if (used[i]) continue;
     if (aijcluclu(i,ic) < fgkCouplMin) continue;
     used[i] = kTRUE;
@@ -159,12 +162,13 @@ AliMUONClusterSplitterMLEM::BinToPix(TH2 *mlem,
   AliMUONPad *pixPtr = NULL;
   
   // Compare pixel and bin positions
-  for (Int_t i=0; i<nPix; i++) {
+  for (Int_t i = 0; i < nPix; ++i) {
     pixPtr = (AliMUONPad*) fPixArray->UncheckedAt(i);
     if (pixPtr->Charge() < 0.5) continue;
     if (TMath::Abs(pixPtr->Coord(0)-xc)<1.e-4 && TMath::Abs(pixPtr->Coord(1)-yc)<1.e-4) 
     {
-      return (TObject*) pixPtr;
+      //return (TObject*) pixPtr;
+      return pixPtr;
     }
   }
   AliError(Form(" Something wrong ??? %f %f ", xc, yc));
@@ -190,48 +194,52 @@ AliMUONClusterSplitterMLEM::ChargeIntegration(Double_t x, Double_t y,
 void 
 AliMUONClusterSplitterMLEM::Fcn1(const AliMUONCluster& cluster, 
                                     Int_t & /*fNpar*/, Double_t * /*gin*/, 
-                                    Double_t &f, Double_t *par, Int_t /*iflag*/)
+                                    Double_t &f, Double_t *par, Int_t iflag)
 {
-  /// Fit for one track
+  /// Computes the functional to be minimized
   
   Int_t indx, npads=0;
   Double_t charge, delta, coef=0, chi2=0, qTot = 0;
+  static Double_t qAver = 0;
   
-  for (Int_t j=0; j< cluster.Multiplicity(); ++j) 
+  Int_t mult = cluster.Multiplicity(), iend = fNpar / 3;
+  for (Int_t j = 0; j < mult; ++j) 
   {
     AliMUONPad* pad = cluster.Pad(j);
-    if ( pad->Status() !=1 || pad->IsSaturated() ) continue;
-    if ( pad->IsReal() ) npads++; // exclude virtual pads
-    qTot += pad->Charge(); // c.fXyq[2][j];
+    //if ( pad->Status() !=1 || pad->IsSaturated() ) continue;
+    if ( pad->Status() != AliMUONClusterFinderMLEM::GetUseForFitFlag()) continue;
+    if (iflag == 0) {
+      if ( pad->IsReal() ) npads++; // exclude virtual pads
+      qTot += pad->Charge(); 
+    }
     charge = 0;
-    for (Int_t i=fNpar/3; i>=0; --i)
-    { // sum over tracks
-      indx = i<2 ? 2*i : 2*i+1;
-      if (fNpar == 2) 
-      {
-        coef = 1;
-      }
-      else 
-      {
-        coef = i==fNpar/3 ? par[indx+2] : 1-coef;
-      }
-      coef = TMath::Max (coef, 0.);
-      if ( fNpar == 8 && i < 2) 
-      {
-        coef = i==1 ? coef*par[indx+2] : coef - par[7];
-      }
-      coef = TMath::Max (coef, 0.);
+    for (Int_t i = 0; i <= iend; ++i)
+    { 
+      // sum over hits
+      indx = 3 * i;
+      coef = Param2Coef(i, coef, par);
       charge += ChargeIntegration(par[indx],par[indx+1],*pad) * coef;
     }
     charge *= fQtot;
-    delta = charge - pad->Charge(); //c.fXyq[2][j];
+    delta = charge - pad->Charge(); 
     delta *= delta;
-    delta /= pad->Charge(); //c.fXyq[2][j];
+    delta /= pad->Charge(); 
     chi2 += delta;
   } // for (Int_t j=0;
-  f = chi2; 
-  Double_t qAver = qTot/npads;
-  f = chi2/qAver;
+  if (iflag == 0) qAver = qTot / npads;
+  f = chi2 / qAver;
+}
+
+//_____________________________________________________________________________
+Double_t AliMUONClusterSplitterMLEM::Param2Coef(Int_t icand, Double_t coef, Double_t *par)
+{
+  /// Extract hit contribution scale factor from fit parameters
+  
+  if (fNpar == 2) return 1.;
+  if (fNpar == 5) return icand==0 ? par[2] : TMath::Max(1.-par[2],0.);
+  if (icand == 0) return par[2];
+  if (icand == 1) return TMath::Max((1.-par[2])*par[5], 0.);
+  return TMath::Max(1.-par[2]-coef,0.);
 }
 
 //_____________________________________________________________________________
@@ -240,44 +248,45 @@ AliMUONClusterSplitterMLEM::Fit(const AliMUONCluster& cluster,
                                 Int_t iSimple, Int_t nfit, 
                                 Int_t *clustFit, TObjArray **clusters, 
                                 Double_t *parOk,
-                                TObjArray& clusterList)
+                                TObjArray& clusterList, TH2 *mlem)
 {
-  /// Find selected clusters to selected pad charges
+  /// Steering function and fitting procedure for the fit of pad charge distribution
   
   //  AliDebug(2,Form("iSimple=%d nfit=%d",iSimple,nfit));
   
-  TH2D *mlem = (TH2D*) gROOT->FindObject("mlem");
   Double_t xmin = mlem->GetXaxis()->GetXmin() - mlem->GetXaxis()->GetBinWidth(1);
   Double_t xmax = mlem->GetXaxis()->GetXmax() + mlem->GetXaxis()->GetBinWidth(1);
   Double_t ymin = mlem->GetYaxis()->GetXmin() - mlem->GetYaxis()->GetBinWidth(1);
   Double_t ymax = mlem->GetYaxis()->GetXmax() + mlem->GetYaxis()->GetBinWidth(1);
-  Double_t step[3]={0.01,0.002,0.02}, xPad = 0, yPad = 99999;
+  Double_t xPad = 0, yPad = 99999;
   
   // Number of pads to use and number of virtual pads
   Int_t npads = 0, nVirtual = 0, nfit0 = nfit;
   //cluster.Print("full");
-  for (Int_t i=0; i<cluster.Multiplicity(); ++i ) 
+  Int_t mult = cluster.Multiplicity();
+  for (Int_t i = 0; i < mult; ++i ) 
   {
     AliMUONPad* pad = cluster.Pad(i);
     if ( !pad->IsReal() ) ++nVirtual;
-    if ( pad->Status() !=1 || pad->IsSaturated() ) continue;
+    //if ( pad->Status() !=1 || pad->IsSaturated() ) continue;
+    if ( pad->Status() != AliMUONClusterFinderMLEM::GetUseForFitFlag() ) continue;
     if ( pad->IsReal() )
     {
       ++npads;
       if (yPad > 9999) 
       { 
-        xPad = pad->X();//fXyq[0][i]; 
-        yPad = pad->Y();//fXyq[1][i]; 
+        xPad = pad->X();
+        yPad = pad->Y();
       } 
       else 
       {
-        if (pad->DY() < pad->DX() ) //fXyq[4][i] < fXyq[3][i]) 
+        if (pad->DY() < pad->DX() ) 
         {
-          yPad = pad->Y();//fXyq[1][i]; 
+          yPad = pad->Y();
         }
         else 
         {
-          xPad = pad->X();//fXyq[0][i]; 
+          xPad = pad->X();
         }
       }
     }
@@ -323,19 +332,19 @@ AliMUONClusterSplitterMLEM::Fit(const AliMUONCluster& cluster,
    */
   
   // Get number of pads in X and Y 
-//  Int_t nInX = 0, nInY;
-//  PadsInXandY(cluster,nInX, nInY);
-  const Int_t kStatusToTest(1);
+  //const Int_t kStatusToTest(1);
+  const Int_t kStatusToTest(AliMUONClusterFinderMLEM::GetUseForFitFlag());
   
-  AliMpIntPair nofPads = cluster.NofPads(kStatusToTest);
-  Int_t nInX = nofPads.GetFirst();
-  Int_t nInY = nofPads.GetSecond();
+  Long_t nofPads = cluster.NofPads(kStatusToTest);
+  Int_t nInX = AliMp::PairFirst(nofPads);
+  Int_t nInY = AliMp::PairSecond(nofPads);
 
   if (fDebug) {
     Int_t npadOK = 0;
     for (Int_t j = 0; j < cluster.Multiplicity(); ++j) {
       AliMUONPad *pad = cluster.Pad(j);
-      if (pad->Status() == 1 && !pad->IsSaturated()) npadOK++;
+      //if (pad->Status() == 1 && !pad->IsSaturated()) npadOK++;
+      if (pad->Status() == AliMUONClusterFinderMLEM::GetUseForFitFlag() && !pad->IsSaturated()) npadOK++;
     }
     cout << " Number of pads to fit: " << npadOK << endl;
     cout << " nInX and Y: " << nInX << " " << nInY << endl;
@@ -344,7 +353,7 @@ AliMUONClusterSplitterMLEM::Fit(const AliMUONCluster& cluster,
   Int_t nfitMax = 3; 
   nfitMax = TMath::Min (nfitMax, (npads + 1) / 3);
   if (nfitMax > 1) {
-    if (nInX < 3 && nInY < 3 || nInX == 3 && nInY < 3 || nInX < 3 && nInY == 3) nfitMax = 1; // not enough pads in each direction
+    if (((nInX < 3) && (nInY < 3)) || ((nInX == 3) && (nInY < 3)) || ((nInX < 3) && (nInY == 3))) nfitMax = 1; // not enough pads in each direction
   }
   if (nfit > nfitMax) nfit = nfitMax;
   
@@ -355,13 +364,13 @@ AliMUONClusterSplitterMLEM::Fit(const AliMUONCluster& cluster,
   Double_t cont, cmax = 0, xseed = 0, yseed = 0, errOk[8], qq = 0;
   Double_t xyseed[3][2], qseed[3], xyCand[3][2] = {{0},{0}}, sigCand[3][2] = {{0},{0}};
   
-  for (Int_t ifit=1; ifit<=nfit0; ifit++) 
+  for (Int_t ifit = 1; ifit <= nfit0; ++ifit) 
   {
     cmax = 0;
     pix = clusters[clustFit[ifit-1]];
     npxclu = pix->GetEntriesFast();
     //qq = 0;
-    for (Int_t clu=0; clu<npxclu; ++clu) 
+    for (Int_t clu = 0; clu < npxclu; ++clu) 
     {
       pixPtr = (AliMUONPad*) pix->UncheckedAt(clu);
       cont = pixPtr->Charge();
@@ -392,373 +401,380 @@ AliMUONClusterSplitterMLEM::Fit(const AliMUONCluster& cluster,
   if (fDebug) cout << xyCand[0][0] << " " << xyCand[0][1] << " " << sigCand[0][0] << " " << sigCand[0][1] << endl;
   
   Int_t nDof, maxSeed[3];//, nMax = 0;
-    Double_t fmin, chi2o = 9999, chi2n;
     
-    TMath::Sort(nfit0, qseed, maxSeed, kTRUE); // in decreasing order
+  TMath::Sort(nfit0, qseed, maxSeed, kTRUE); // in decreasing order
     
-    Double_t *gin = 0, func0, func1, param[8], step0[8];
-    Double_t param0[2][8]={{0},{0}}, deriv[2][8]={{0},{0}}; 
-    Double_t shift[8], stepMax, derMax, parmin[8], parmax[8], func2[2], shift0;
-    Double_t delta[8], scMax, dder[8], estim, shiftSave = 0;
-    Int_t min, max, nCall = 0, nLoop, idMax = 0, iestMax = 0, nFail;
-    Double_t rad, dist[3] = {0};
+  Double_t step[3]={0.01,0.002,0.02}, fmin, chi2o = 9999, chi2n;
+  Double_t *gin = 0, func0, func1, param[8], step0[8];
+  Double_t param0[2][8]={{0},{0}}, deriv[2][8]={{0},{0}}; 
+  Double_t shift[8], stepMax, derMax, parmin[8], parmax[8], func2[2], shift0;
+  Double_t delta[8], scMax, dder[8], estim, shiftSave = 0;
+  Int_t min, max, nCall = 0, nLoop, idMax = 0, iestMax = 0, nFail;
+  Double_t rad, dist[3] = {0};
     
-    // Try to fit with one-track hypothesis, then 2-track. If chi2/dof is 
-    // lower, try 3-track (if number of pads is sufficient).
-    for (Int_t iseed=0; iseed<nfit; iseed++) 
-    {
-      
-      Int_t memory[8] = {0};
-      if (iseed) 
-      { 
-        for (Int_t j=0; j<fNpar; j++) 
-        {
-          param[j] = parOk[j]; 
-        }
-      } // for bounded params
+  // Try to fit with one-track hypothesis, then 2-track. If chi2/dof is 
+  // lower, try 3-track (if number of pads is sufficient).
+  Int_t iflag = 0; // for the first call of fcn1
+  for (Int_t iseed = 0; iseed < nfit; ++iseed) 
+  {
       
-      for (Int_t j=0; j<3; j++) 
+    Int_t memory[8] = {0};
+    if (iseed) 
+    { 
+      for (Int_t j = 0; j < fNpar; ++j) 
       {
-        step0[fNpar+j] = shift[fNpar+j] = step[j];
+	param[j] = parOk[j]; 
       }
+      param[fNpar] = 0.6;
+      parmin[fNpar] = 0; 
+      parmax[fNpar++] = 1; 
+    }
       
-      if (nfit == 1) 
-      {
-        param[fNpar] = xyCand[0][0]; // take COG
-      }
-      else 
-      {
-        param[fNpar] = xyseed[maxSeed[iseed]][0];
-      }
-      parmin[fNpar] = xmin; 
-      parmax[fNpar++] = xmax; 
-      if (nfit == 1) 
-      {
-        param[fNpar] = xyCand[0][1]; // take COG
-      }
-      else 
-      {
-        param[fNpar] = xyseed[maxSeed[iseed]][1];
-      }
-      parmin[fNpar] = ymin; 
-      parmax[fNpar++] = ymax; 
-      if (fNpar > 2) 
+    if (nfit == 1) 
+    {
+      param[fNpar] = xyCand[0][0]; // take COG
+    }
+    else 
+    {
+      param[fNpar] = xyseed[maxSeed[iseed]][0];
+      //param[fNpar] = fNpar==0 ? -16.1651 : -15.2761; 
+    }
+    parmin[fNpar] = xmin; 
+    parmax[fNpar++] = xmax; 
+    if (nfit == 1) 
+    {
+      param[fNpar] = xyCand[0][1]; // take COG
+    }
+    else 
+    {
+      param[fNpar] = xyseed[maxSeed[iseed]][1];
+      //param[fNpar] = fNpar==1 ? -15.1737 : -15.8487;
+    }
+    parmin[fNpar] = ymin; 
+    parmax[fNpar++] = ymax; 
+
+    for (Int_t j = 0; j < fNpar; ++j) 
+    {
+      step0[j] = shift[j] = step[j%3];
+    }
+
+    if (iseed) 
+    { 
+      for (Int_t j = 0; j < fNpar; ++j) 
       {
-        param[fNpar] = fNpar == 4 ? 0.5 : 0.3;
-        parmin[fNpar] = 0; 
-        parmax[fNpar++] = 1; 
-      }
-      if (iseed) 
-      { 
-        for (Int_t j=0; j<fNpar; j++) 
-        {
-          param0[1][j] = 0; 
-        }
+	param0[1][j] = 0; 
       }
+    }
+    if (fDebug) {
+      for (Int_t j = 0; j < fNpar; ++j) cout << param[j] << " "; 
+      cout << endl;
+    }
+      
+    // Try new algorithm
+    min = nLoop = 1; stepMax = func2[1] = derMax = 999999; nFail = 0;
       
-      // Try new algorithm
-      min = nLoop = 1; stepMax = func2[1] = derMax = 999999; nFail = 0;
+    while (1) 
+    {
+      max = !min;
+      Fcn1(cluster,fNpar, gin, func0, param, iflag); nCall++;
+      iflag = 1;
+      //cout << " Func: " << func0 << endl;
       
-      while (1) 
+      func2[max] = func0;
+      for (Int_t j = 0; j < fNpar; ++j) 
       {
-        max = !min;
-        Fcn1(cluster,fNpar, gin, func0, param, 1); nCall++;
-        //cout << " Func: " << func0 << endl;
-        
-        func2[max] = func0;
-        for (Int_t j=0; j<fNpar; j++) 
-        {
-          param0[max][j] = param[j];
-          delta[j] = step0[j];
-          param[j] += delta[j] / 10;
-          if (j > 0) param[j-1] -= delta[j-1] / 10;
-          Fcn1(cluster,fNpar, gin, func1, param, 1); nCall++;
-          deriv[max][j] = (func1 - func0) / delta[j] * 10; // first derivative
-                                                           //cout << j << " " << deriv[max][j] << endl;
-          dder[j] = param0[0][j] != param0[1][j] ? (deriv[0][j] - deriv[1][j]) / 
-            (param0[0][j] - param0[1][j]) : 0; // second derivative
-        }
-        param[fNpar-1] -= delta[fNpar-1] / 10;
-        if (nCall > 2000) break;
+	param0[max][j] = param[j];
+	delta[j] = step0[j];
+	param[j] += delta[j] / 10;
+	if (j > 0) param[j-1] -= delta[j-1] / 10;
+	Fcn1(cluster,fNpar, gin, func1, param, iflag); nCall++;
+	deriv[max][j] = (func1 - func0) / delta[j] * 10; // first derivative
+	//cout << j << " " << deriv[max][j] << endl;
+	dder[j] = param0[0][j] != param0[1][j] ? (deriv[0][j] - deriv[1][j]) / 
+	  (param0[0][j] - param0[1][j]) : 0; // second derivative
+      }
+      param[fNpar-1] -= delta[fNpar-1] / 10;
+      if (nCall > 2000) break;
         
-        min = func2[0] < func2[1] ? 0 : 1;
-        nFail = min == max ? 0 : nFail + 1;
+      min = func2[0] < func2[1] ? 0 : 1;
+      nFail = min == max ? 0 : nFail + 1;
         
-        stepMax = derMax = estim = 0;
-        for (Int_t j=0; j<fNpar; j++) 
-        { 
-          // Estimated distance to minimum
-          shift0 = shift[j];
-          if (nLoop == 1) 
-          {
-            shift[j] = TMath::Sign (step0[j], -deriv[max][j]); // first step
-          }
-          else if (TMath::Abs(deriv[0][j]) < 1.e-3 && TMath::Abs(deriv[1][j]) < 1.e-3) 
-          {
-            shift[j] = 0;
-          }
-          else if (deriv[min][j]*deriv[!min][j] > 0 && TMath::Abs(deriv[min][j]) > TMath::Abs(deriv[!min][j])
-                   || TMath::Abs(deriv[0][j]-deriv[1][j]) < 1.e-3 || TMath::Abs(dder[j]) < 1.e-6) 
-          {
-            shift[j] = -TMath::Sign (shift[j], (func2[0]-func2[1]) * (param0[0][j]-param0[1][j]));
-	    if (min == max) 
+      stepMax = derMax = estim = 0;
+      for (Int_t j = 0; j < fNpar; ++j) 
+      { 
+	// Estimated distance to minimum
+	shift0 = shift[j];
+	if (nLoop == 1) 
+        {
+	  shift[j] = TMath::Sign (step0[j], -deriv[max][j]); // first step
+	}
+	else if (TMath::Abs(deriv[0][j]) < 1.e-3 && TMath::Abs(deriv[1][j]) < 1.e-3) 
+        {
+	  shift[j] = 0;
+	}
+	else if (((deriv[min][j]*deriv[!min][j] > 0) && (TMath::Abs(deriv[min][j]) > TMath::Abs(deriv[!min][j])))
+		 || (TMath::Abs(deriv[0][j]-deriv[1][j]) < 1.e-3) || (TMath::Abs(dder[j]) < 1.e-6)) 
+        {
+	  shift[j] = -TMath::Sign (shift[j], (func2[0]-func2[1]) * (param0[0][j]-param0[1][j]));
+	  if (min == max) 
+	  { 
+	    if (memory[j] > 1) 
 	    { 
-	      if (memory[j] > 1) 
-	      { 
-		shift[j] *= 2; 
-	      } 
-	      memory[j]++;
-	    }
+	      shift[j] *= 2; 
+	    } 
+	    memory[j]++;
 	  }
-          else 
-          {
-            shift[j] = dder[j] != 0 ? -deriv[min][j] / dder[j] : 0;
-            memory[j] = 0;
-          }
-          
-          if (TMath::Abs(shift[j])/step0[j] > estim) 
-          { 
-            estim = TMath::Abs(shift[j])/step0[j];
-            iestMax = j;
-          }
+	}
+	else 
+        {
+	  shift[j] = dder[j] != 0 ? -deriv[min][j] / dder[j] : 0;
+	  memory[j] = 0;
+	}
           
-          // Too big step
-          if (TMath::Abs(shift[j])/step0[j] > 10) shift[j] = TMath::Sign(10.,shift[j]) * step0[j]; // 
+	Double_t es = TMath::Abs(shift[j]) / step0[j];
+	if (es > estim) 
+        { 
+	  estim = es;
+	  iestMax = j;
+	}
           
-          // Failed to improve minimum
-          if (min != max) 
+	// Too big step
+	if (TMath::Abs(shift[j])/step0[j] > 10) shift[j] = TMath::Sign(10.,shift[j]) * step0[j]; // 
+	
+	// Failed to improve minimum
+	if (min != max) 
+        {
+	  memory[j] = 0;
+	  param[j] = param0[min][j];
+	  if (TMath::Abs(shift[j]+shift0) > 0.1*step0[j]) 
           {
-            memory[j] = 0;
-            param[j] = param0[min][j];
-            if (TMath::Abs(shift[j]+shift0) > 0.1*step0[j]) 
-            {
-              shift[j] = (shift[j] + shift0) / 2;
-            }
-            else 
-            {
-              shift[j] /= -2;
-            }
-          } 
-          
-          // Too big step
-          if (TMath::Abs(shift[j]*deriv[min][j]) > func2[min]) 
+	    shift[j] = (shift[j] + shift0) / 2;
+	  }
+	  else 
           {
-            shift[j] = TMath::Sign (func2[min]/deriv[min][j], shift[j]);
-          }
+	    shift[j] /= -2;
+	  }
+	} 
           
-          // Introduce step relaxation factor
-          if (memory[j] < 3) 
-          {
-            scMax = 1 + 4 / TMath::Max(nLoop/2.,1.);
-            if (TMath::Abs(shift0) > 0 && TMath::Abs(shift[j]/shift0) > scMax) 
-            {
-              shift[j] = TMath::Sign (shift0*scMax, shift[j]);
-            }
-          }
-          param[j] += shift[j]; 
-          //MLEM Check parameter limits 27-12-2004
-          if (param[j] < parmin[j]) 
-          { 
-            shift[j] = parmin[j] - param[j]; 
-            param[j] = parmin[j]; 
-          } 
-          else if (param[j] > parmax[j]) 
-          {
-            shift[j] = parmax[j] - param[j];
-            param[j] = parmax[j];
-          }
-          //cout << " xxx " << j << " " << shift[j] << " " << param[j] << endl;
-          stepMax = TMath::Max (stepMax, TMath::Abs(shift[j]/step0[j]));
-          if (TMath::Abs(deriv[min][j]) > derMax) 
+	// Too big step
+	if (TMath::Abs(shift[j]*deriv[min][j]) > func2[min]) 
+        {
+	  shift[j] = TMath::Sign (func2[min]/deriv[min][j], shift[j]);
+	}
+          
+	// Introduce step relaxation factor
+	if (memory[j] < 3) 
+        {
+	  scMax = 1 + 4 / TMath::Max(nLoop/2.,1.);
+	  if (TMath::Abs(shift0) > 0 && TMath::Abs(shift[j]/shift0) > scMax) 
           {
-            idMax = j;
-            derMax = TMath::Abs (deriv[min][j]);
-          }
-        } // for (Int_t j=0; j<fNpar;
+	    shift[j] = TMath::Sign (shift0*scMax, shift[j]);
+	  }
+	}
+	param[j] += shift[j]; 
+	// Check parameter limits
+	if (param[j] < parmin[j]) 
+        { 
+	  shift[j] = parmin[j] - param[j]; 
+	  param[j] = parmin[j]; 
+	} 
+	else if (param[j] > parmax[j]) 
+        {
+	  shift[j] = parmax[j] - param[j];
+	  param[j] = parmax[j];
+	}
+	//cout << " xxx " << j << " " << shift[j] << " " << param[j] << endl;
+	stepMax = TMath::Max (stepMax, TMath::Abs(shift[j]/step0[j]));
+	if (TMath::Abs(deriv[min][j]) > derMax) 
+        {
+	  idMax = j;
+	  derMax = TMath::Abs (deriv[min][j]);
+	}
+      } // for (Int_t j=0; j<fNpar;
         
-        if (estim < 1 && derMax < 2 || nLoop > 150) break; // minimum was found
+      if (((estim < 1) && (derMax < 2)) || nLoop > 150) break; // minimum was found
         
-        nLoop++;
+      nLoop++;
         
-        // Check for small step
-        if (shift[idMax] == 0) 
-        { 
-          shift[idMax] = step0[idMax]/10; 
-          param[idMax] += shift[idMax]; 
-          continue; 
-        }
+      // Check for small step
+      if (shift[idMax] == 0) 
+      { 
+	shift[idMax] = step0[idMax]/10; 
+	param[idMax] += shift[idMax]; 
+	continue; 
+      }
         
-        if (!memory[idMax] && derMax > 0.5 && nLoop > 10) 
+      if (!memory[idMax] && derMax > 0.5 && nLoop > 10) 
+      {
+	if (dder[idMax] != 0 && TMath::Abs(deriv[min][idMax]/dder[idMax]/shift[idMax]) > 10) 
         {
-          if (dder[idMax] != 0 && TMath::Abs(deriv[min][idMax]/dder[idMax]/shift[idMax]) > 10) 
-          {
-            if (min == max) dder[idMax] = -dder[idMax];
-            shift[idMax] = -deriv[min][idMax] / dder[idMax] / 10; 
-            param[idMax] += shift[idMax];
-            stepMax = TMath::Max (stepMax, TMath::Abs(shift[idMax])/step0[idMax]);
-            if (min == max) shiftSave = shift[idMax];
-          }
-          if (nFail > 10) 
-          {
-            param[idMax] -= shift[idMax];
-            shift[idMax] = 4 * shiftSave * (gRandom->Rndm(0) - 0.5);
-            param[idMax] += shift[idMax];
-          }
-        }      
-  } // while (1)
+	  if (min == max) dder[idMax] = -dder[idMax];
+	  shift[idMax] = -deriv[min][idMax] / dder[idMax] / 10; 
+	  param[idMax] += shift[idMax];
+	  stepMax = TMath::Max (stepMax, TMath::Abs(shift[idMax])/step0[idMax]);
+	  if (min == max) shiftSave = shift[idMax];
+	}
+	if (nFail > 10) 
+        {
+	  param[idMax] -= shift[idMax];
+	  shift[idMax] = 4 * shiftSave * (gRandom->Rndm(0) - 0.5);
+	  param[idMax] += shift[idMax];
+	}
+      }      
+    } // while (1)
       
-      fmin = func2[min];
+    fmin = func2[min];
+    
+    nDof = npads - fNpar + nVirtual;
+    if (!nDof) nDof++;
+    chi2n = fmin / nDof;
+    if (fDebug) cout << " Chi2 " << chi2n << " " << fNpar << endl;
       
-      nDof = npads - fNpar + nVirtual;
-      if (!nDof) nDof++;
-      chi2n = fmin / nDof;
-      if (fDebug) cout << " Chi2 " << chi2n << " " << fNpar << endl;
+    //if (fNpar > 2) cout << param0[min][fNpar-3] << " " << chi2n * (1+TMath::Min(1-param0[min][fNpar-3],0.25)) << endl;
+    //if (chi2n*1.2+1.e-6 > chi2o ) 
+    if (fNpar > 2 && (chi2n > chi2o || ((iseed == nfit-1) 
+					&& (chi2n * (1+TMath::Min(1-param0[min][fNpar-3],0.25)) > chi2o)))) 
+      { fNpar -= 3; break; }
       
-      if (chi2n*1.2+1.e-6 > chi2o ) { fNpar -= 3; break; }
+    // Save parameters and errors
       
-      // Save parameters and errors
+    if (nInX == 1) {
+      // One pad per direction 
+      //for (Int_t i=0; i<fNpar; ++i) if (i == 0 || i == 2 || i == 5) param0[min][i] = xPad;
+      for (Int_t i=0; i<fNpar; ++i) if (i == 0 || i == 2 || i == 5) 
+	param0[min][i] = xyCand[0][0];
+    }
+    if (nInY == 1) {
+      // One pad per direction 
+      //for (Int_t i=0; i<fNpar; ++i) if (i == 1 || i == 3 || i == 6) param0[min][i] = yPad;
+      for (Int_t i=0; i<fNpar; ++i) if (i == 1 || i == 3 || i == 6) 
+	param0[min][i] = xyCand[0][1];
+    }
       
-      if (nInX == 1) {
-        // One pad per direction 
-        for (Int_t i=0; i<fNpar; i++) if (i == 0 || i == 2 || i == 5) param0[min][i] = xPad;
+    /*
+      if (iseed > 0) {
+      // Find distance to the nearest neighbour
+      dist[0] = dist[1] = TMath::Sqrt ((param0[min][0]-param0[min][2])*
+      (param0[min][0]-param0[min][2])
+      +(param0[min][1]-param0[min][3])*
+      (param0[min][1]-param0[min][3]));
+      if (iseed > 1) {
+      dist[2] = TMath::Sqrt ((param0[min][0]-param0[min][5])*
+      (param0[min][0]-param0[min][5])
+      +(param0[min][1]-param0[min][6])*
+      (param0[min][1]-param0[min][6]));
+      rad = TMath::Sqrt ((param0[min][2]-param0[min][5])*
+      (param0[min][2]-param0[min][5])
+      +(param0[min][3]-param0[min][6])*
+      (param0[min][3]-param0[min][6]));
+      if (dist[2] < dist[0]) dist[0] = dist[2];
+      if (rad < dist[1]) dist[1] = rad;
+      if (rad < dist[2]) dist[2] = rad;
       }
-      if (nInY == 1) {
-        // One pad per direction 
-        for (Int_t i=0; i<fNpar; i++) if (i == 1 || i == 3 || i == 6) param0[min][i] = yPad;
+      cout << dist[0] << " " << dist[1] << " " << dist[2] << endl;
+      if (dist[TMath::LocMin(iseed+1,dist)] < 1.) { fNpar -= 3; break; }
       }
+    */
       
-      /*
-       if (iseed > 0) {
-         // Find distance to the nearest neighbour
-         dist[0] = dist[1] = TMath::Sqrt ((param0[min][0]-param0[min][2])*
-                                          (param0[min][0]-param0[min][2])
-                                          +(param0[min][1]-param0[min][3])*
-                                          (param0[min][1]-param0[min][3]));
-         if (iseed > 1) {
-           dist[2] = TMath::Sqrt ((param0[min][0]-param0[min][5])*
-                                  (param0[min][0]-param0[min][5])
-                                  +(param0[min][1]-param0[min][6])*
-                                  (param0[min][1]-param0[min][6]));
-           rad = TMath::Sqrt ((param0[min][2]-param0[min][5])*
-                              (param0[min][2]-param0[min][5])
-                              +(param0[min][3]-param0[min][6])*
-                              (param0[min][3]-param0[min][6]));
-           if (dist[2] < dist[0]) dist[0] = dist[2];
-           if (rad < dist[1]) dist[1] = rad;
-           if (rad < dist[2]) dist[2] = rad;
-         }
-         cout << dist[0] << " " << dist[1] << " " << dist[2] << endl;
-         if (dist[TMath::LocMin(iseed+1,dist)] < 1.) { fNpar -= 3; break; }
-       }
-       */
-      
-      for (Int_t i=0; i<fNpar; i++) {
-        parOk[i] = param0[min][i];
-        //errOk[i] = fmin;
-        errOk[i] = chi2n;
-        // Bounded params
-        parOk[i] = TMath::Max (parOk[i], parmin[i]);
-        parOk[i] = TMath::Min (parOk[i], parmax[i]);
-      }
+    for (Int_t i = 0; i < fNpar; ++i) {
+      parOk[i] = param0[min][i];
+      //errOk[i] = fmin;
+      errOk[i] = chi2n;
+      // Bounded params
+      parOk[i] = TMath::Max (parOk[i], parmin[i]);
+      parOk[i] = TMath::Min (parOk[i], parmax[i]);
+    }
       
-      chi2o = chi2n;
-      if (fmin < 0.1) break; // !!!???
-    } // for (Int_t iseed=0; 
+    chi2o = chi2n;
+    if (fmin < 0.1) break; // !!!???
+  } // for (Int_t iseed=0; 
    
-    if (fDebug) {
-      for (Int_t i=0; i<fNpar; i++) {
-        if (i == 4 || i == 7) {
-          if (i == 7 || i == 4 && fNpar < 7) cout << parOk[i] << endl;
-          else cout << parOk[i] * (1-parOk[7]) << endl;
-          continue;
-        }
-        cout << parOk[i] << " " << errOk[i] << endl;
+  if (fDebug) {
+    for (Int_t i=0; i<fNpar; ++i) {
+      if (i == 4 || i == 7) {
+	if ((i == 7) || ((i == 4) && (fNpar < 7))) cout << parOk[i] << endl;
+	else cout << parOk[i] * (1-parOk[7]) << endl;
+	continue;
       }
+      cout << parOk[i] << " " << errOk[i] << endl;
     }
-    nfit = (fNpar + 1) / 3;
-    dist[0] = dist[1] = dist[2] = 0;
-    
-    if (nfit > 1) {
-      // Find distance to the nearest neighbour
-      dist[0] = dist[1] = TMath::Sqrt ((parOk[0]-parOk[2])*
-                                       (parOk[0]-parOk[2])
-                                       +(parOk[1]-parOk[3])*
-                                       (parOk[1]-parOk[3]));
-      if (nfit > 2) {
-        dist[2] = TMath::Sqrt ((parOk[0]-parOk[5])*
-                               (parOk[0]-parOk[5])
-                               +(parOk[1]-parOk[6])*
-                               (parOk[1]-parOk[6]));
-        rad = TMath::Sqrt ((parOk[2]-parOk[5])*
-                           (parOk[2]-parOk[5])
-                           +(parOk[3]-parOk[6])*
-                           (parOk[3]-parOk[6]));
-        if (dist[2] < dist[0]) dist[0] = dist[2];
-        if (rad < dist[1]) dist[1] = rad;
-        if (rad < dist[2]) dist[2] = rad;
-      }
+  }
+  nfit = (fNpar + 1) / 3;
+  dist[0] = dist[1] = dist[2] = 0;
+  
+  if (nfit > 1) {
+    // Find distance to the nearest neighbour
+    dist[0] = dist[1] = TMath::Sqrt ((parOk[0]-parOk[2])*
+				     (parOk[0]-parOk[2])
+				     +(parOk[1]-parOk[3])*
+				     (parOk[1]-parOk[3]));
+    if (nfit > 2) {
+      dist[2] = TMath::Sqrt ((parOk[0]-parOk[5])*
+			     (parOk[0]-parOk[5])
+			     +(parOk[1]-parOk[6])*
+			     (parOk[1]-parOk[6]));
+      rad = TMath::Sqrt ((parOk[2]-parOk[5])*
+			 (parOk[2]-parOk[5])
+			 +(parOk[3]-parOk[6])*
+			 (parOk[3]-parOk[6]));
+      if (dist[2] < dist[0]) dist[0] = dist[2];
+      if (rad < dist[1]) dist[1] = rad;
+      if (rad < dist[2]) dist[2] = rad;
     }
+  }
     
-    Int_t indx;
-    
-    //if (!fDraw) {
+  Int_t indx;
+  
+  Double_t coef = 0;
+  if (iSimple) fnCoupled = 0;
+  for (Int_t j = 0; j < nfit; ++j) {
+    indx = 3 * j;
+    coef = Param2Coef(j, coef, parOk);
+      
+    //void AliMUONClusterFinderMLEM::AddRawCluster(Double_t x, Double_t y, 
+    //                                             Double_t qTot, Double_t fmin,
+    //                                             Int_t nfit, Int_t *tracks, 
+    //                                             Double_t /*sigx*/, 
+    //                                             Double_t /*sigy*/, 
+    //                                             Double_t /*dist*/)
     
-    Double_t coef = 0;
-    if (iSimple) fnCoupled = 0;
-    //for (Int_t j=0; j<nfit; j++) {
-    for (Int_t j=nfit-1; j>=0; j--) {
-      indx = j<2 ? j*2 : j*2+1;  
-      if (nfit == 1) coef = 1;
-      else coef = j==nfit-1 ? parOk[indx+2] : 1-coef;
-      coef = TMath::Max (coef, 0.);
-      if (nfit == 3 && j < 2) coef = j==1 ? coef*parOk[indx+2] : coef - parOk[7];
-      coef = TMath::Max (coef, 0.);
+    if ( coef*fQtot >= 14 )
+    {
+      //AZ AliMUONCluster* cluster1 = new AliMUONCluster();
+      AliMUONCluster* cluster1 = new AliMUONCluster(cluster);
       
-      //void AliMUONClusterFinderMLEM::AddRawCluster(Double_t x, Double_t y, 
-      //                                             Double_t qTot, Double_t fmin,
-      //                                             Int_t nfit, Int_t *tracks, 
-      //                                             Double_t /*sigx*/, 
-      //                                             Double_t /*sigy*/, 
-      //                                             Double_t /*dist*/)
+      cluster1->SetCharge(coef*fQtot,coef*fQtot);
+      cluster1->SetPosition(TVector2(parOk[indx],parOk[indx+1]),TVector2(sigCand[0][0],sigCand[0][1]));
+      cluster1->SetChi2(dist[TMath::LocMin(nfit,dist)]);
       
-      if ( coef*fQtot >= 14 )
-      {
-        //AZ AliMUONCluster* cluster1 = new AliMUONCluster();
-        AliMUONCluster* cluster1 = new AliMUONCluster(cluster);
-        
-        cluster1->SetCharge(coef*fQtot,coef*fQtot);
-        cluster1->SetPosition(TVector2(parOk[indx],parOk[indx+1]),TVector2(sigCand[0][0],sigCand[0][1]));
-        cluster1->SetChi2(dist[TMath::LocMin(nfit,dist)]);
-        
-        // FIXME: we miss some information in this cluster, as compared to 
-        // the original AddRawCluster code.
-        
-        AliDebug(2,Form("Adding RawCluster detElemId %4d mult %2d charge %5d (xl,yl)=(%9.6g,%9.6g)",
-                        fDetElemId,cluster1->Multiplicity(),(Int_t)cluster1->Charge(),
-                        cluster1->Position().X(),cluster1->Position().Y()));
+      // FIXME: we miss some information in this cluster, as compared to 
+      // the original AddRawCluster code.
+      
+      AliDebug(2,Form("Adding RawCluster detElemId %4d mult %2d charge %5d (xl,yl)=(%9.6g,%9.6g)",
+		      fDetElemId,cluster1->Multiplicity(),(Int_t)cluster1->Charge(),
+		      cluster1->Position().X(),cluster1->Position().Y()));
         
-        clusterList.Add(cluster1);
-      }
-      //      AddRawCluster (parOk[indx], // double x
-      //                     parOk[indx+1], // double y
-      //                     coef*qTot, // double charge
-      //                     errOk[indx], // double fmin
-      //                     nfit0+10*nfit+100*nMax+10000*fnCoupled, // int nfit
-      //                     tracks, // int* tracks
-      //                     sigCand[0][0], // double sigx
-      //                     sigCand[0][1], // double sigy
-      //                     dist[TMath::LocMin(nfit,dist)] // double dist
-      //                     );
+      clusterList.Add(cluster1);
     }
-    return nfit;
-    }  
+    //      AddRawCluster (parOk[indx], // double x
+    //                     parOk[indx+1], // double y
+    //                     coef*qTot, // double charge
+    //                     errOk[indx], // double fmin
+    //                     nfit0+10*nfit+100*nMax+10000*fnCoupled, // int nfit
+    //                     tracks, // int* tracks
+    //                     sigCand[0][0], // double sigx
+    //                     sigCand[0][1], // double sigy
+    //                     dist[TMath::LocMin(nfit,dist)] // double dist
+    //                     );
+  }
+  return nfit;
+}  
 
 
 //_____________________________________________________________________________
 void
 AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
-                                  TH2 *mlem,
-                                  Double_t *coef,
+                                  TH2 *mlem, Double_t *coef,
                                   TObjArray& clusterList)
 {
   /// The main steering function to work with clusters of pixels in anode
@@ -769,19 +785,19 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
   Int_t ny = mlem->GetNbinsY();
   Int_t nPix = fPixArray->GetEntriesFast();
   
-  Bool_t *used = new Bool_t[ny*nx];
   Double_t cont;
-  Int_t nclust = 0, indx, indx1;
+  Int_t nclust = 0, indx, indx1, nxy = ny * nx; 
+  Bool_t *used = new Bool_t[nxy];
   
-  for (Int_t i=0; i<ny*nx; i++) used[i] = kFALSE; 
+  for (Int_t j = 0; j < nxy; ++j) used[j] = kFALSE; 
   
   TObjArray *clusters[200]={0};
   TObjArray *pix;
   
   // Find clusters of histogram bins (easier to work in 2-D space)
-  for (Int_t i=1; i<=ny; i++) 
+  for (Int_t i = 1; i <= ny; ++i) 
   {
-    for (Int_t j=1; j<=nx; j++) 
+    for (Int_t j = 1; j <= nx; ++j) 
     {
       indx = (i-1)*nx + j - 1;
       if (used[indx]) continue;
@@ -794,15 +810,16 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       if (nclust >= 200) AliFatal(" Too many clusters !!!");
       clusters[nclust++] = pix;
     } // for (Int_t j=1; j<=nx; j++) {
-    } // for (Int_t i=1; i<=ny;
-//  if (fDebug) cout << nclust << endl;
-  delete [] used; used = 0;
+  } // for (Int_t i=1; i<=ny;
+  if (fDebug) cout << nclust << endl;
+  delete [] used;
   
   // Compute couplings between clusters and clusters to pads
   Int_t npad = cluster.Multiplicity();
   
   // Exclude pads with overflows
-  for (Int_t j=0; j<npad; ++j) 
+  /*
+  for (Int_t j = 0; j < npad; ++j) 
   {
     AliMUONPad* pad = cluster.Pad(j);
     if ( pad->IsSaturated() )
@@ -814,37 +831,39 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       pad->SetStatus(0);
     }
   }
+  */
   
-  // Compute couplings of clusters to pads
+  // Compute couplings of clusters to pads (including overflows)
   TMatrixD aijclupad(nclust,npad);
   aijclupad = 0;
   Int_t npxclu;
-  for (Int_t iclust=0; iclust<nclust; ++iclust) 
+  for (Int_t iclust = 0; iclust < nclust; ++iclust) 
   {
     pix = clusters[iclust];
     npxclu = pix->GetEntriesFast();
-    for (Int_t i=0; i<npxclu; ++i) 
+    for (Int_t i = 0; i < npxclu; ++i) 
     {
       indx = fPixArray->IndexOf(pix->UncheckedAt(i));
-      for (Int_t j=0; j<npad; ++j) 
+      for (Int_t j = 0; j < npad; ++j) 
       {
-        AliMUONPad* pad = cluster.Pad(j);
-        if ( pad->Status() < 0 && pad->Status() != -5) continue;
+        //AliMUONPad* pad = cluster.Pad(j);
+        //if ( pad->Status() < 0 && pad->Status() != -5) continue;
         if (coef[j*nPix+indx] < fgkCouplMin) continue;
         aijclupad(iclust,j) += coef[j*nPix+indx];
       }
     }
   }
   
-  // Compute couplings between clusters
+  // Compute couplings between clusters (exclude overflows)
   TMatrixD aijcluclu(nclust,nclust);
   aijcluclu = 0;
-  for (Int_t iclust=0; iclust<nclust; ++iclust) 
+  for (Int_t iclust = 0; iclust < nclust; ++iclust) 
   {
-    for (Int_t j=0; j<npad; ++j) 
+    for (Int_t j = 0; j < npad; ++j) 
     {
       // Exclude overflows
-      if ( cluster.Pad(j)->Status() < 0) continue;
+      //if ( cluster.Pad(j)->Status() < 0) continue;
+      if ( cluster.Pad(j)->IsSaturated()) continue;
       if (aijclupad(iclust,j) < fgkCouplMin) continue;
       for (Int_t iclust1=iclust+1; iclust1<nclust; iclust1++) 
       {
@@ -854,22 +873,26 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       }
     }
   }
-  for (Int_t iclust=0; iclust<nclust; ++iclust) 
+  for (Int_t iclust = 0; iclust < nclust; ++iclust) 
   {
-    for (Int_t iclust1=iclust+1; iclust1<nclust; ++iclust1) 
+    for (Int_t iclust1 = iclust+1; iclust1 < nclust; ++iclust1) 
     {
       aijcluclu(iclust1,iclust) = aijcluclu(iclust,iclust1);
     }
   }
   
+  if (fDebug && nclust > 1) aijcluclu.Print();
+
   // Find groups of coupled clusters
   used = new Bool_t[nclust];
-  for (Int_t i=0; i<nclust; i++) used[i] = kFALSE;
+  for (Int_t j = 0; j < nclust; ++j) used[j] = kFALSE;
+
   Int_t *clustNumb = new Int_t[nclust];
   Int_t nCoupled, nForFit, minGroup[3], clustFit[3], nfit = 0;
-  Double_t parOk[8];
+  //Double_t parOk[8];
+  Double_t parOk[8] = {0}; //AZ
   
-  for (Int_t igroup=0; igroup<nclust; igroup++) 
+  for (Int_t igroup = 0; igroup < nclust; ++igroup) 
   {
     if (used[igroup]) continue;
     used[igroup] = kTRUE;
@@ -878,10 +901,10 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
     // Find group of coupled clusters
     AddCluster(igroup, nclust, aijcluclu, used, clustNumb, nCoupled); // recursive
     
-    //    if (fDebug) {                                                                      
-    //      cout << " nCoupled: " << nCoupled << endl;                                                                      
-    //      for (Int_t i=0; i<nCoupled; i++) cout << clustNumb[i] << " "; cout << endl;                                                                       
-    //    }
+    if (fDebug) {                                                                      
+      cout << " nCoupled: " << nCoupled << endl;
+      for (Int_t i=0; i<nCoupled; ++i) cout << clustNumb[i] << " "; cout << endl;
+    }
     
     fnCoupled = nCoupled;
     
@@ -890,35 +913,40 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       if (nCoupled < 4) 
       {
         nForFit = nCoupled;
-        for (Int_t i=0; i<nCoupled; i++) clustFit[i] = clustNumb[i];
+        for (Int_t i = 0; i < nCoupled; ++i) clustFit[i] = clustNumb[i];
       } 
       else 
       {
         // Too many coupled clusters to fit - try to decouple them
         // Find the lowest coupling of 1, 2, min(3,nLinks/2) pixels with 
         // all the others in the group 
-        for (Int_t j=0; j<3; j++) minGroup[j] = -1;
-        /*Double_t coupl =*/ MinGroupCoupl(nCoupled, clustNumb, aijcluclu, minGroup);
+        for (Int_t j = 0; j < 3; ++j) minGroup[j] = -1;
+        Double_t coupl = MinGroupCoupl(nCoupled, clustNumb, aijcluclu, minGroup);
         
         // Flag clusters for fit
         nForFit = 0;
         while (minGroup[nForFit] >= 0 && nForFit < 3)
         {
+          if (fDebug) cout << clustNumb[minGroup[nForFit]] << " ";
           clustFit[nForFit] = clustNumb[minGroup[nForFit]];
           clustNumb[minGroup[nForFit]] -= 999;
           nForFit++;
         }
+        if (fDebug) cout << " nForFit " << nForFit << " " << coupl << endl;
       } // else
       
       // Select pads for fit. 
       if (SelectPad(cluster,nCoupled, nForFit, clustNumb, clustFit, aijclupad) < 3 && nCoupled > 1) 
       {
         // Deselect pads
-        for (Int_t j=0; j<npad; ++j)
+        for (Int_t j = 0; j < npad; ++j)
         {
           AliMUONPad* pad = cluster.Pad(j);
-          if ( pad->Status()==1 ) pad->SetStatus(0);
-          if ( pad->Status()==-9) pad->SetStatus(-5);
+          //if ( pad->Status()==1 ) pad->SetStatus(0);
+          //if ( pad->Status()==-9) pad->SetStatus(-5);
+          if ( pad->Status() == AliMUONClusterFinderMLEM::GetUseForFitFlag() ||
+	       pad->Status() == AliMUONClusterFinderMLEM::GetCoupledFlag()) 
+	    pad->SetStatus(AliMUONClusterFinderMLEM::GetZeroFlag());
         }
         // Merge the failed cluster candidates (with too few pads to fit) with 
         // the one with the strongest coupling
@@ -927,7 +955,11 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       else 
       {
         // Do the fit
-        nfit = Fit(cluster,0, nForFit, clustFit, clusters, parOk, clusterList);
+        nfit = Fit(cluster,0, nForFit, clustFit, clusters, parOk, clusterList, mlem);
+	if (nfit == 0) { 
+	  //cout << " (nfit == 0) " << fNpar << " " << cluster.Multiplicity() << endl; 
+	  fNpar = 0; // should be 0 by itself but just in case ...
+	}
       }
       
       // Subtract the fitted charges from pads with strong coupling and/or
@@ -935,11 +967,13 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       UpdatePads(cluster,nfit, parOk);
       
       // Mark used pads
-      for (Int_t j=0; j<npad; ++j) 
+      for (Int_t j = 0; j < npad; ++j) 
       {
         AliMUONPad* pad = cluster.Pad(j);
-        if ( pad->Status()==1 ) pad->SetStatus(-1);
-        if ( pad->Status()==-9) pad->SetStatus(-5);
+	//if ( pad->Status()==1 ) pad->SetStatus(-2);
+	//if ( pad->Status()==-9) pad->SetStatus(-5);
+	if ( pad->Status() == AliMUONClusterFinderMLEM::GetUseForFitFlag() ) 
+	  pad->SetStatus(AliMUONClusterFinderMLEM::GetModifiedFlag());
       }
       
       // Sort the clusters (move to the right the used ones)
@@ -947,7 +981,7 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       while (beg < end) 
       {
         if (clustNumb[beg] >= 0) { ++beg; continue; }
-        for (Int_t j=end; j>beg; --j) 
+        for (Int_t j = end; j > beg; --j) 
         {
           if (clustNumb[j] < 0) continue;
           end = j - 1;
@@ -963,27 +997,28 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
       if (nCoupled > 3) 
       {
         // Remove couplings of used clusters
-        for (Int_t iclust=nCoupled; iclust<nCoupled+nForFit;++ iclust) 
+        for (Int_t iclust = nCoupled; iclust < nCoupled+nForFit; ++iclust) 
         {
           indx = clustNumb[iclust] + 999;
-          for (Int_t iclust1=0; iclust1<nCoupled; ++iclust1) 
+          for (Int_t iclust1 = 0; iclust1 < nCoupled; ++iclust1) 
           {
             indx1 = clustNumb[iclust1];
             aijcluclu(indx,indx1) = aijcluclu(indx1,indx) = 0;
           }
         }
         
-        // Update the remaining clusters couplings (exclude couplings from 
-        // the used pads)
-        for (Int_t j=0; j<npad; ++j) 
+        // Update the remaining clusters couplings (subtract couplings from 
+        // the used pads) - overflows excluded
+        for (Int_t j = 0; j < npad; ++j) 
         {
           AliMUONPad* pad = cluster.Pad(j);
-          if ( pad->Status() != -1) continue;
+          //if ( pad->Status() != -2) continue;
+          if ( pad->Status() != AliMUONClusterFinderMLEM::GetModifiedFlag()) continue;
           for (Int_t iclust=0; iclust<nCoupled; ++iclust) 
           {
             indx = clustNumb[iclust];
             if (aijclupad(indx,j) < fgkCouplMin) continue;
-            for (Int_t iclust1=iclust+1; iclust1<nCoupled; ++iclust1) 
+            for (Int_t iclust1 = iclust+1; iclust1 < nCoupled; ++iclust1) 
             {
               indx1 = clustNumb[iclust1];
               if (aijclupad(indx1,j) < fgkCouplMin) continue;
@@ -993,23 +1028,21 @@ AliMUONClusterSplitterMLEM::Split(const AliMUONCluster& cluster,
               aijcluclu(indx1,indx) = aijcluclu(indx,indx1);
             }
           }
-          pad->SetStatus(-8);
+          //pad->SetStatus(-8);
+          pad->SetStatus(AliMUONClusterFinderMLEM::GetOverFlag());
         } // for (Int_t j=0; j<npad;
       } // if (nCoupled > 3)
     } // while (nCoupled > 0)
   } // for (Int_t igroup=0; igroup<nclust;
   
-  for (Int_t iclust=0; iclust<nclust; iclust++)
+  for (Int_t iclust = 0; iclust < nclust; ++iclust)
   {
     pix = clusters[iclust]; 
     pix->Clear();
     delete pix; 
-    pix = 0;
   }
   delete [] clustNumb; 
-  clustNumb = 0; 
   delete [] used; 
-  used = 0;
 
 }
 
@@ -1027,13 +1060,13 @@ AliMUONClusterSplitterMLEM::Merge(const AliMUONCluster& cluster,
   TObjArray *pix, *pix1;
   Double_t couplMax;
   
-  for (Int_t icl=0; icl<nForFit; ++icl) 
+  for (Int_t icl = 0; icl < nForFit; ++icl) 
   {
     indx = clustFit[icl];
     pix = clusters[indx];
     npxclu = pix->GetEntriesFast();
     couplMax = -1;
-    for (Int_t icl1=0; icl1<nCoupled; ++icl1) 
+    for (Int_t icl1 = 0; icl1 < nCoupled; ++icl1) 
     {
       indx1 = clustNumb[icl1];
       if (indx1 < 0) continue;
@@ -1047,14 +1080,14 @@ AliMUONClusterSplitterMLEM::Merge(const AliMUONCluster& cluster,
     pix1 = clusters[imax];
     npxclu1 = pix1->GetEntriesFast();
     // Add pixels 
-    for (Int_t i=0; i<npxclu; ++i) 
+    for (Int_t i = 0; i < npxclu; ++i) 
     { 
       pix1->Add(pix->UncheckedAt(i)); 
       pix->RemoveAt(i); 
     }
     
     //Add cluster-to-cluster couplings
-    for (Int_t icl1=0; icl1<nCoupled; ++icl1) 
+    for (Int_t icl1 = 0; icl1 < nCoupled; ++icl1) 
     {
       indx1 = clustNumb[icl1];
       if (indx1 < 0 || indx1 == imax) continue;
@@ -1064,10 +1097,12 @@ AliMUONClusterSplitterMLEM::Merge(const AliMUONCluster& cluster,
     aijcluclu(indx,imax) = aijcluclu(imax,indx) = 0;
     
     //Add cluster-to-pad couplings
-    for (Int_t j=0; j<cluster.Multiplicity(); ++j) 
+    Int_t mult = cluster.Multiplicity();
+    for (Int_t j = 0; j < mult; ++j) 
     {
       AliMUONPad* pad = cluster.Pad(j);
-      if ( pad->Status() < 0 && pad->Status() != -5 ) continue;// exclude used pads
+      //if ( pad->Status() < 0 && pad->Status() != -5 ) continue;// exclude used pads
+      if ( pad->Status() != AliMUONClusterFinderMLEM::GetZeroFlag()) continue;// exclude used pads
         aijclupad(imax,j) += aijclupad(indx,j);
         aijclupad(indx,j) = 0;
     }
@@ -1086,25 +1121,25 @@ AliMUONClusterSplitterMLEM::MinGroupCoupl(Int_t nCoupled, Int_t *clustNumb,
   Int_t indx, indx1, indx2, indx3, nTot = 0;
   Double_t *coupl1 = 0, *coupl2 = 0, *coupl3 = 0;
   
-  for (Int_t i123=1; i123<=i123max; i123++) {
+  for (Int_t i123 = 1; i123 <= i123max; ++i123) {
     
     if (i123 == 1) {
       coupl1 = new Double_t [nCoupled];
-      for (Int_t i=0; i<nCoupled; i++) coupl1[i] = 0;
+      for (Int_t i = 0; i < nCoupled; ++i) coupl1[i] = 0;
     }
     else if (i123 == 2) {
       nTot = nCoupled*nCoupled;
       coupl2 = new Double_t [nTot];
-      for (Int_t i=0; i<nTot; i++) coupl2[i] = 9999;
+      for (Int_t i = 0; i < nTot; ++i) coupl2[i] = 9999;
     } else {
       nTot = nTot*nCoupled;
       coupl3 = new Double_t [nTot];
-      for (Int_t i=0; i<nTot; i++) coupl3[i] = 9999;
+      for (Int_t i = 0; i < nTot; ++i) coupl3[i] = 9999;
     } // else
     
-    for (Int_t i=0; i<nCoupled; i++) {
+    for (Int_t i = 0; i < nCoupled; ++i) {
       indx1 = clustNumb[i];
-      for (Int_t j=i+1; j<nCoupled; j++) {
+      for (Int_t j = i+1; j < nCoupled; ++j) {
         indx2 = clustNumb[j];
         if (i123 == 1) {
           coupl1[i] += aijcluclu(indx1,indx2);
@@ -1115,7 +1150,7 @@ AliMUONClusterSplitterMLEM::MinGroupCoupl(Int_t nCoupled, Int_t *clustNumb,
           coupl2[indx] = coupl1[i] + coupl1[j];
           coupl2[indx] -= 2 * (aijcluclu(indx1,indx2));
         } else {
-          for (Int_t k=j+1; k<nCoupled; k++) {
+          for (Int_t k = j+1; k < nCoupled; ++k) {
             indx3 = clustNumb[k];
             indx = i*nCoupled*nCoupled + j*nCoupled + k;
             coupl3[indx] = coupl2[i*nCoupled+j] + coupl1[k];
@@ -1130,12 +1165,12 @@ AliMUONClusterSplitterMLEM::MinGroupCoupl(Int_t nCoupled, Int_t *clustNumb,
   Double_t couplMin = 9999;
   Int_t locMin = 0;
   
-  for (Int_t i123=1; i123<=i123max; i123++) {
+  for (Int_t i123 = 1; i123 <= i123max; ++i123) {
     if (i123 == 1) {
       locMin = TMath::LocMin(nCoupled, coupl1);
       couplMin = coupl1[locMin];
       minGroup[0] = locMin;
-      delete [] coupl1; coupl1 = 0;
+      delete [] coupl1;
     } 
     else if (i123 == 2) {
       locMin = TMath::LocMin(nCoupled*nCoupled, coupl2);
@@ -1144,7 +1179,7 @@ AliMUONClusterSplitterMLEM::MinGroupCoupl(Int_t nCoupled, Int_t *clustNumb,
         minGroup[0] = locMin/nCoupled;
         minGroup[1] = locMin%nCoupled;
       }
-      delete [] coupl2; coupl2 = 0;
+      delete [] coupl2;
     } else {
       locMin = TMath::LocMin(nTot, coupl3);
       if (coupl3[locMin] < couplMin) {
@@ -1153,7 +1188,7 @@ AliMUONClusterSplitterMLEM::MinGroupCoupl(Int_t nCoupled, Int_t *clustNumb,
         minGroup[1] = locMin%(nCoupled*nCoupled)/nCoupled;
         minGroup[2] = locMin%nCoupled;
       }
-      delete [] coupl3; coupl3 = 0;
+      delete [] coupl3; 
     } // else
   } // for (Int_t i123=1;
   return couplMin;
@@ -1175,28 +1210,35 @@ AliMUONClusterSplitterMLEM::SelectPad(const AliMUONCluster& cluster,
   if (nCoupled > 3) 
   {
     padpix = new Double_t[npad];
-    for (Int_t i=0; i<npad; i++) padpix[i] = 0; 
+    for (Int_t i = 0; i < npad; ++i) padpix[i] = 0.;
   }
   
   Int_t nOK = 0, indx, indx1;
-  for (Int_t iclust=0; iclust<nForFit; ++iclust)
+  for (Int_t iclust = 0; iclust < nForFit; ++iclust)
   {
     indx = clustFit[iclust];
-    for (Int_t j=0; j<npad; j++) 
+    for (Int_t j = 0; j < npad; ++j) 
     {
       if ( aijclupad(indx,j) < fgkCouplMin) continue;
       AliMUONPad* pad = cluster.Pad(j);
-      if ( pad->Status() == -5 ) pad->SetStatus(-0); // flag overflow
+      /*
+      if ( pad->Status() == -5 ) pad->SetStatus(-9); // flag overflow
       if ( pad->Status() < 0 ) continue; // exclude overflows and used pads
       if ( !pad->Status() ) 
       {
         pad->SetStatus(1);
         ++nOK; // pad to be used in fit
       }      
+      */
+      if ( pad->Status() != AliMUONClusterFinderMLEM::GetZeroFlag() 
+	   || pad->IsSaturated() ) continue; // used pads and overflows
+      pad->SetStatus(AliMUONClusterFinderMLEM::GetUseForFitFlag());
+      ++nOK; // pad to be used in fit
+
       if (nCoupled > 3) 
       {
         // Check other clusters
-        for (Int_t iclust1=0; iclust1<nCoupled; ++iclust1) 
+        for (Int_t iclust1 = 0; iclust1 < nCoupled; ++iclust1) 
         {
           indx1 = clustNumb[iclust1];
           if (indx1 < 0) continue;
@@ -1209,15 +1251,15 @@ AliMUONClusterSplitterMLEM::SelectPad(const AliMUONCluster& cluster,
   if (nCoupled < 4) return nOK;
   
   Double_t aaa = 0;
-  for (Int_t j=0; j<npad; ++j) 
+  for (Int_t j = 0; j < npad; ++j) 
   {
     if (padpix[j] < fgkCouplMin) continue;
     aaa += padpix[j];
-    cluster.Pad(j)->SetStatus(-1); // exclude pads with strong coupling to the other clusters
+    //cluster.Pad(j)->SetStatus(-1); // exclude pads with strong coupling to the other clusters
+    cluster.Pad(j)->SetStatus(AliMUONClusterFinderMLEM::GetCoupledFlag()); // exclude pads with strong coupling to the other clusters
     nOK--;
   }
   delete [] padpix; 
-  padpix = 0;
   return nOK;
 }
 
@@ -1228,42 +1270,32 @@ AliMUONClusterSplitterMLEM::UpdatePads(const AliMUONCluster& cluster,
 {
   /// Subtract the fitted charges from pads with strong coupling
   
-  Int_t indx;
+  Int_t indx, mult = cluster.Multiplicity(), iend = fNpar/3;
   Double_t charge, coef=0;
   
-  for (Int_t j=0; j<cluster.Multiplicity(); ++j) 
+  for (Int_t j = 0; j < mult; ++j) 
   {
     AliMUONPad* pad = cluster.Pad(j);
-    if ( pad->Status() != -1 ) continue;
+    //if ( pad->Status() != -1 ) continue;
+    if ( pad->Status() != AliMUONClusterFinderMLEM::GetCoupledFlag() ) continue;
     if (fNpar != 0) 
     {
       charge = 0;
-      for (Int_t i=fNpar/3; i>=0; --i) 
+      for (Int_t i = 0; i <= iend; ++i) 
       { 
-        // sum over tracks
-        indx = i<2 ? 2*i : 2*i+1;
-        if (fNpar == 2) 
-        {
-          coef = 1;
-        }
-        else 
-        {
-          coef = i==fNpar/3 ? par[indx+2] : 1-coef;
-        }
-        coef = TMath::Max (coef, 0.);
-        if (fNpar == 8 && i < 2) 
-        {
-          coef = i==1 ? coef*par[indx+2] : coef - par[7];
-        }
-        coef = TMath::Max (coef, 0.);
+        // sum over hits
+	indx = 3 * i;
+	coef = Param2Coef(i, coef, par);
         charge += ChargeIntegration(par[indx],par[indx+1],*pad) * coef;
       }
       charge *= fQtot;
       pad->SetCharge(pad->Charge()-charge);
     } // if (fNpar != 0)
     
-    if (pad->Charge() > 6 /*fgkZeroSuppression*/) pad->SetStatus(0); 
+    //if (pad->Charge() > 6 /*fgkZeroSuppression*/) pad->SetStatus(0); 
+    if (pad->Charge() > 6 /*fgkZeroSuppression*/) pad->SetStatus(AliMUONClusterFinderMLEM::GetZeroFlag()); 
     // return pad for further using // FIXME: remove usage of zerosuppression here
+    else pad->SetStatus(AliMUONClusterFinderMLEM::GetOverFlag()); // do not use anymore
     
   } // for (Int_t j=0;
 }