class TH3: public TH1, public TAtt3D

 Default constructor.

-*-*-*-*Normal constructor for fix bin size 3-D histograms
*-*              ==================================================

-*-*-*-*Normal constructor for variable bin size 3-D histograms
*-*            =======================================================

-*-*-*-*Normal constructor for variable bin size 3-D histograms
*-*            =======================================================

 Copy constructor.
 The list of functions is not copied. (Use Clone if needed)

 Destructor.

 Copy.

 Fill histogram with all entries in the buffer.
 action = -1 histogram is reset and refilled from the buffer (called by THistPainter::Paint)
 action =  0 histogram is filled from the buffer
 action =  1 histogram is filled and buffer is deleted
             The buffer is automatically deleted when the number of entries
             in the buffer is greater than the number of entries in the histogram

 accumulate arguments in buffer. When buffer is full, empty the buffer
 fBuffer[0] = number of entries in buffer
 fBuffer[1] = w of first entry
 fBuffer[2] = x of first entry
 fBuffer[3] = y of first entry
 fBuffer[4] = z of first entry

-*-*-*-*-*-*Increment cell defined by x,y,z by 1 
*-*                  ====================================
-
-

-*-*-*-*-*-*Increment cell defined by x,y,z by a weight w
*-*                  =============================================
-
*-* If the storage of the sum of squares of weights has been triggered,
*-* via the function Sumw2, then the sum of the squares of weights is incremented
*-* by w^2 in the cell corresponding to x,y,z.
-
-

 Increment cell defined by namex,namey,namez by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

 Increment cell defined by namex,y,namez by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

 Increment cell defined by namex,namey,z by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

 Increment cell defined by x,namey,namezz by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

 Increment cell defined by x,namey,z by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

 Increment cell defined by x,y,namez by a weight w

 If the storage of the sum of squares of weights has been triggered,
 via the function Sumw2, then the sum of the squares of weights is incremented
 by w^2 in the cell corresponding to x,y,z.

-*-*-*Fill histogram following distribution in function fname
*-*          =======================================================
-
*-*   The distribution contained in the function fname (TF1) is integrated
*-*   over the channel contents.
*-*   It is normalized to 1.
*-*   Getting one random number implies:
*-*     - Generating a random number between 0 and 1 (say r1)
*-*     - Look in which bin in the normalized integral r1 corresponds to
*-*     - Fill histogram channel
*-*   ntimes random numbers are generated
-
*-*  One can also call TF1::GetRandom to get a random variate from a function.
-
*

-*-*-*Fill histogram following distribution in histogram h
*-*          ====================================================
-
*-*   The distribution contained in the histogram h (TH3) is integrated
*-*   over the channel contents.
*-*   It is normalized to 1.
*-*   Getting one random number implies:
*-*     - Generating a random number between 0 and 1 (say r1)
*-*     - Look in which bin in the normalized integral r1 corresponds to
*-*     - Fill histogram channel
*-*   ntimes random numbers are generated
-
*

 Project slices along Z in case of a 3-D histogram, then fit each slice
 with function f1 and make a 2-d histogram for each fit parameter
 Only cells in the bin range [binminx,binmaxx] and [binminy,binmaxy] are considered.
 if f1=0, a gaussian is assumed
 Before invoking this function, one can set a subrange to be fitted along Z
 via f1->SetRange(zmin,zmax)
 The argument option (default="QNR") can be used to change the fit options.
     "Q" means Quiet mode
     "N" means do not show the result of the fit
     "R" means fit the function in the specified function range

 Note that the generated histograms are added to the list of objects
 in the current directory. It is the user's responsability to delete
 these histograms.

  Example: Assume a 3-d histogram h3
   Root > h3->FitSlicesZ(); produces 4 TH2D histograms
          with h3_0 containing parameter 0(Constant) for a Gaus fit
                    of each cell in X,Y projected along Z
          with h3_1 containing parameter 1(Mean) for a gaus fit
          with h3_2 containing parameter 2(RMS)  for a gaus fit
          with h3_chi2 containing the chisquare/number of degrees of freedom for a gaus fit

   Root > h3->Fit(0,15,22,0,0,10);
          same as above, but only for bins 15 to 22 along X
          and only for cells in X,Y for which the corresponding projection
          along Z has more than cut bins filled.

  NOTE: To access the generated histograms in the current directory, do eg:
     TH2D *h3_1 = (TH2D*)gDirectory->Get("h3_1");

 compute first cell (binx,biny,binz) in the range [firstx,lastx](firsty,lasty][firstz,lastz] for which
 diff = abs(cell_content-c) <= maxdiff
 In case several cells in the specified range with diff=0 are found
 the first cell found is returned in binx,biny,binz.
 In case several cells in the specified range satisfy diff <=maxdiff
 the cell with the smallest difference is returned in binx,biny,binz.
 In all cases the function returns the smallest difference.

 NOTE1: if firstx <= 0, firstx is set to bin 1
        if (lastx < firstx then firstx is set to the number of bins in X
        ie if firstx=0 and lastx=0 (default) the search is on all bins in X.
        if firsty <= 0, firsty is set to bin 1
        if (lasty < firsty then firsty is set to the number of bins in Y
        ie if firsty=0 and lasty=0 (default) the search is on all bins in Y.
        if firstz <= 0, firstz is set to bin 1
        if (lastz < firstz then firstz is set to the number of bins in Z
        ie if firstz=0 and lastz=0 (default) the search is on all bins in Z.
 NOTE2: if maxdiff=0 (default), the first cell with content=c is returned.

-*-*-*Return correlation factor between axis1 and axis2
*-*            ====================================================

-*-*-*Return covariance between axis1 and axis2
*-*            ====================================================

 return 3 random numbers along axis x , y and z distributed according
 the cellcontents of a 3-dim histogram

 fill the array stats from the contents of this histogram
 The array stats must be correctly dimensionned in the calling program.
 stats[0] = sumw
 stats[1] = sumw2
 stats[2] = sumwx
 stats[3] = sumwx2
 stats[4] = sumwy
 stats[5] = sumwy2
 stats[6] = sumwxy
 stats[7] = sumwz
 stats[8] = sumwz2
 stats[9] = sumwxz
 stats[10]= sumwyz

Return integral of bin contents. Only bins in the bins range are considered.
 By default the integral is computed as the sum of bin contents in the range.
 if option "width" is specified, the integral is the sum of
 the bin contents multiplied by the bin width in x, y and in z.

Return integral of bin contents in range [binx1,binx2],[biny1,biny2],[binz1,binz2]
 for a 3-D histogram
 By default the integral is computed as the sum of bin contents in the range.
 if option "width" is specified, the integral is the sum of
 the bin contents multiplied by the bin width in x, y and in z.

  Statistical test of compatibility in shape between
  THIS histogram and h2, using Kolmogorov test.
     Default: Ignore under- and overflow bins in comparison

     option is a character string to specify options
         "U" include Underflows in test
         "O" include Overflows
         "N" include comparison of normalizations
         "D" Put out a line of "Debug" printout
         "M" Return the Maximum Kolmogorov distance instead of prob

   The returned function value is the probability of test
       (much less than one means NOT compatible)

   The KS test uses the distance between the pseudo-CDF's obtained
   from the histogram. Since in more than 1D the order for generating the pseudo-CDF is
   arbitrary, we use the pseudo-CDF's obtained from all the possible 6 combinatons of the 3 axis.
   The average of all the maximum  distances obtained is used in the tests.

Add all histograms in the collection to this histogram.
This function computes the min/max for the axes,
compute a new number of bins, if necessary,
add bin contents, errors and statistics.
If overflows are present and limits are different the function will fail.
The function returns the total number of entries in the result histogram
if the merge is successfull, -1 otherwise.

IMPORTANT remark. The 2 axis x and y may have different number
of bins and different limits, BUT the largest bin width must be
a multiple of the smallest bin width and the upper limit must also
be a multiple of the bin width.

Project a 3-D histogram into a 1-D histogram along Z*-*-
*-*      ====================================================

   The projection is always of the type TH1D.
   The projection is made from the cells along the X axis
   ranging from ixmin to ixmax and iymin to iymax included.
   By default, bins 1 to nx and 1 to ny  are included

   if option "e" is specified, the errors are computed.
   if option "d" is specified, the projection is drawn in the current pad.

  implemented using Project3D

 Project a 3-d histogram into 1 or 2-d histograms depending on the
 option parameter
 option may contain a combination of the characters x,y,z,e
 option = "x" return the x projection into a TH1D histogram
 option = "y" return the y projection into a TH1D histogram
 option = "z" return the z projection into a TH1D histogram
 option = "xy" return the x versus y projection into a TH2D histogram
 option = "yx" return the y versus x projection into a TH2D histogram
 option = "xz" return the x versus z projection into a TH2D histogram
 option = "zx" return the z versus x projection into a TH2D histogram
 option = "yz" return the y versus z projection into a TH2D histogram
 option = "zy" return the z versus y projection into a TH2D histogram

 If option contains the string "e", errors are computed

 The projection is made for the selected bins only.
 To select a bin range along an axis, use TAxis::SetRange, eg
    h3.GetYaxis()->SetRange(23,56);

 NOTE 1: The generated histogram is named th3name + option
 eg if the TH3* h histogram is named "myhist", then
 h->Project3D("xy"); produces a TH2D histogram named "myhist_xy"
 if a histogram of the same type already exists, it is overwritten.
 The following sequence
    h->Project3D("xy");
    h->Project3D("xy2");
  will generate two TH2D histograms named "myhist_xy" and "myhist_xy2"

  NOTE 2: The number of entries in the projected histogram is estimated from the number of
  effective entries for all the cells included in the projection.

  NOTE 3: underflow/overflow are included by default in the projection
  To exclude underflow and/or overflow (for both axis in case of a projection to a 1D histogram) use option "NUF" and/or "NOF"
  With SetRange() you can have all bin except underflow/overflow only if you set the axis bit range as
 following after having called SetRange:
    axis->SetRange(1, axis->GetNbins());
    axis->SetBit(TAxis::kAxisRange);

 Project a 3-d histogram into a 2-d profile histograms depending
 on the option parameter
 option may contain a combination of the characters x,y,z
 option = "xy" return the x versus y projection into a TProfile2D histogram
 option = "yx" return the y versus x projection into a TProfile2D histogram
 option = "xz" return the x versus z projection into a TProfile2D histogram
 option = "zx" return the z versus x projection into a TProfile2D histogram
 option = "yz" return the y versus z projection into a TProfile2D histogram
 option = "zy" return the z versus y projection into a TProfile2D histogram

 The projection is made for the selected bins only.
 To select a bin range along an axis, use TAxis::SetRange, eg
    h3.GetYaxis()->SetRange(23,56);

 NOTE 1: The generated histogram is named th3name + _poption
 eg if the TH3* h histogram is named "myhist", then
 h->Project3D("xy"); produces a TProfile2D histogram named "myhist_pxy"
 if a histogram of the same type already exists, it is deleted.
 The following sequence
    h->Project3DProfile("xy");
    h->Project3DProfile("xy2");
  will generate two TProfile2D histograms named "myhist_pxy" and "myhist_pxy2"

  NOTE 2: The number of entries in the projected profile is estimated from the number of
  effective entries for all the cells included in the projection.

  NOTE 3: underflow/overflow are by default excluded from the projection
  (Note that this is a different default behavior compared to the projection to an histogram)
  To exclude underflow and/or overflow (for both axis in case of a projection to a 1D histogram) use option "UF" and/or "OF"

 Replace current statistics with the values in array stats

Reset this histogram: contents, errors, etc
*-*            ===========================================

 Stream an object of class TH3.

 When the mouse is moved in a pad containing a 3-d view of this histogram
 a second canvas shows a projection type given as option.
 To stop the generation of the projections, delete the canvas
 containing the projection.
 option may contain a combination of the characters x,y,z,e
 option = "x" return the x projection into a TH1D histogram
 option = "y" return the y projection into a TH1D histogram
 option = "z" return the z projection into a TH1D histogram
 option = "xy" return the x versus y projection into a TH2D histogram
 option = "yx" return the y versus x projection into a TH2D histogram
 option = "xz" return the x versus z projection into a TH2D histogram
 option = "zx" return the z versus x projection into a TH2D histogram
 option = "yz" return the y versus z projection into a TH2D histogram
 option = "zy" return the z versus y projection into a TH2D histogram
 option can also include the drawing option for the projection, eg to draw
 the xy projection using the draw option "box" do
   myhist.SetShowProjection("xy box");
 This function is typically called from the context menu.