From Olivier:

New class TGraph2DErrors, deriving from TGraph2D and implementing
errors in x,y and z.
An example of this class is given in the new tutorial graph2derrorsfit.C


git-svn-id: http://root.cern.ch/svn/root/trunk@7661 27541ba8-7e3a-0410-8455-c3a389f83636

graf/inc/TGraph2DErrors.h

+// @(#)root/graf:$Name:  $:$Id: TGraph2DErrors.h,v 1.00
+// Author: Olivier Couet 26/11/2003
+
+/*************************************************************************
+ * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#ifndef ROOT_TGraph2DErrors
+#define ROOT_TGraph2DErrors
+
+
+//////////////////////////////////////////////////////////////////////////
+//                                                                      //
+// TGraph2DErrors                                                       //
+//                                                                      //
+// a 2D Graph with error bars                                           //
+//                                                                      //
+//////////////////////////////////////////////////////////////////////////
+
+#ifndef ROOT_TGraph2D
+#include "TGraph2D.h"
+#endif
+
+class TGraph2DErrors : public TGraph2D {
+
+protected:
+    Double_t *fEX; //[fNpoints] array of X errors
+    Double_t *fEY; //[fNpoints] array of Y errors
+    Double_t *fEZ; //[fNpoints] array of Z errors
+
+public:
+        TGraph2DErrors();
+        TGraph2DErrors(Int_t n);
+        TGraph2DErrors(Int_t n, Double_t *x, Double_t *y, Double_t *z,
+                                Double_t *ex=0, Double_t *ey=0, Double_t *ez=0, Option_t *option="");
+        virtual ~TGraph2DErrors();
+        Double_t        GetErrorX(Int_t bin) const;
+        Double_t        GetErrorY(Int_t bin) const;
+        Double_t        GetErrorZ(Int_t bin) const;
+        Double_t       *GetEX() const {return fEX;}
+        Double_t       *GetEY() const {return fEY;}
+        Double_t       *GetEZ() const {return fEY;}
+        virtual void    SetPoint(Int_t i, Double_t x, Double_t y, Double_t z);
+        virtual void    SetPointError(Int_t i, Double_t ex, Double_t ey, Double_t ez);
+
+        ClassDef(TGraph2DErrors,3)  //A 2D graph with error bars
+};
+
+#endif
+
+

graf/src/TGraph2DErrors.cxx

+// @(#)root/graf:$Name:  $:$Id: TGraph2DErrors.cxx,v 1.00
+// Author: Olivier Couet
+
+/*************************************************************************
+ * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#include "Riostream.h"
+#include "TROOT.h"
+#include "TGraph2DErrors.h"
+#include "TMath.h"
+#include "TPolyLine.h"
+#include "TPolyMarker.h"
+#include "TVirtualPad.h"
+#include "TVirtualFitter.h"
+#include "TView.h"
+#include "THLimitsFinder.h"
+#include "TStyle.h"
+
+ClassImp(TGraph2DErrors)
+
+//______________________________________________________________________________
+//
+//   A TGraph2DErrors is a TGraph2D with errors.
+//
+
+//______________________________________________________________________________
+TGraph2DErrors::TGraph2DErrors(): TGraph2D()
+{
+   // TGraph2DErrors default constructor
+
+   fEX = 0;
+   fEY = 0;
+   fEZ = 0;
+}
+
+
+//______________________________________________________________________________
+TGraph2DErrors::TGraph2DErrors(Int_t n)
+               : TGraph2D(n)
+{
+   // TGraph2DErrors normal constructor
+   // the arrays are preset to zero
+   
+   if (n <= 0) {
+      Error("TGraph2DErrors", "Invalid number of points (%d)", n);
+      return;
+   }
+
+   fEX = new Double_t[n];
+   fEY = new Double_t[n];
+   fEZ = new Double_t[n];
+
+   for (Int_t i=0;i<n;i++) {
+      fEX[i] = 0;
+      fEY[i] = 0;
+      fEZ[i] = 0;
+   }
+}
+
+
+//______________________________________________________________________________
+TGraph2DErrors::TGraph2DErrors(Int_t n, Double_t *x, Double_t *y, Double_t *z,
+                               Double_t *ex, Double_t *ey, Double_t *ez, Option_t *)
+               :TGraph2D(n, x, y, z)
+{
+   // TGraph2DErrors constructor with doubles vectors as input.
+
+   if (n <= 0) {
+      Error("TGraphErrors", "Invalid number of points (%d)", n);
+      return;
+   }
+        
+   fEX = new Double_t[n];
+   fEY = new Double_t[n];
+   fEZ = new Double_t[n];
+   
+   for (Int_t i=0;i<n;i++) {
+      if (ex) fEX[i] = ex[i];
+      else    fEX[i] = 0;
+      if (ey) fEY[i] = ey[i];
+      else    fEY[i] = 0;
+      if (ey) fEZ[i] = ez[i];
+      else    fEZ[i] = 0;
+   }
+}
+
+
+//______________________________________________________________________________
+TGraph2DErrors::~TGraph2DErrors()
+{
+   // TGraph2DErrors destructor.
+
+   delete [] fEX;
+   delete [] fEY;
+   delete [] fEZ;
+}
+
+
+//______________________________________________________________________________
+Double_t TGraph2DErrors::GetErrorX(Int_t i) const
+{
+   // This function is called by Graph2DFitChisquare.
+   // It returns the error along X at point i.
+
+   if (i < 0 || i >= fNpoints) return -1;
+   if (fEX) return fEX[i];
+   return -1;
+}
+
+
+//______________________________________________________________________________
+Double_t TGraph2DErrors::GetErrorY(Int_t i) const
+{
+   // This function is called by Graph2DFitChisquare.
+   // It returns the error along X at point i.
+
+   if (i < 0 || i >= fNpoints) return -1;
+   if (fEY) return fEY[i];
+   return -1;
+}
+
+
+//______________________________________________________________________________
+Double_t TGraph2DErrors::GetErrorZ(Int_t i) const
+{
+   // This function is called by Graph2DFitChisquare.
+   // It returns the error along X at point i.
+
+   if (i < 0 || i >= fNpoints) return -1;
+   if (fEZ) return fEZ[i];
+   return -1;
+}
+
+
+//______________________________________________________________________________
+void TGraph2DErrors::SetPoint(Int_t i, Double_t x, Double_t y, Double_t z)
+{
+   // Set x, y and z values for point number i
+
+   if (i < 0) return;
+   if (i >= fNpoints) {
+   // re-allocate the object
+      Double_t *savex  = new Double_t[i+1];
+      Double_t *savey  = new Double_t[i+1];
+      Double_t *savez  = new Double_t[i+1];
+      Double_t *saveex = new Double_t[i+1];
+      Double_t *saveey = new Double_t[i+1];
+      Double_t *saveez = new Double_t[i+1];
+      if (fNpoints > 0) {
+         memcpy(savex, fX, fNpoints*sizeof(Double_t));
+         memcpy(savey, fY, fNpoints*sizeof(Double_t));
+         memcpy(savez, fZ, fNpoints*sizeof(Double_t));
+         memcpy(saveex,fEX,fNpoints*sizeof(Double_t));
+         memcpy(saveey,fEY,fNpoints*sizeof(Double_t));
+         memcpy(saveez,fEZ,fNpoints*sizeof(Double_t));
+      }
+      if (fX)  delete [] fX;
+      if (fY)  delete [] fY;
+      if (fZ)  delete [] fZ;
+      if (fEX) delete [] fEX;
+      if (fEY) delete [] fEY;
+      if (fEZ) delete [] fEZ;
+      fX  = savex;
+      fY  = savey;
+      fZ  = savez;
+      fEX = saveex;
+      fEY = saveey;
+      fEZ = saveez;
+      fNpoints = i+1;
+   }
+   fX[i] = x;
+   fY[i] = y;
+   fZ[i] = z;
+}
+
+
+//______________________________________________________________________________
+void TGraph2DErrors::SetPointError(Int_t i, Double_t ex, Double_t ey, Double_t ez)
+{
+   // Set ex, ey and ez values for point number i
+
+   if (i < 0) return;
+   if (i >= fNpoints) {
+      // re-allocate the object
+      TGraph2DErrors::SetPoint(i,0,0,0);
+   }
+   fEX[i] = ex;
+   fEY[i] = ey;
+   fEZ[i] = ez;
+}
+
+
+//______________________________________________________________________________
+void TGraph2DErrors::Streamer(TBuffer &b)
+{
+   // Stream an object of class TGraphErrors.
+
+   if (b.IsReading()) {
+      UInt_t R__s, R__c;
+      Version_t R__v = b.ReadVersion(&R__s, &R__c);
+      TGraph2DErrors::Class()->ReadBuffer(b, this, R__v, R__s, R__c);
+
+      if (!gROOT->ReadingObject()) {
+         fDirectory = gDirectory;
+         if (!gDirectory->GetList()->FindObject(this)) gDirectory->Append(this);
+      }
+      ResetBit(kCanDelete);
+   } else {
+      TGraph2DErrors::Class()->WriteBuffer(b,this);
+   }
+}