class AliTPCDigitizer: public AliDigitizer

 Default ctor - don't use it

 ctor which should be used

 Destructor

 Initialization

DigitizeFast(option);

 Merge input tree's with summable digits
 Output digits stored in TreeTPCD

 Not active for long time.
 Before adding modification (for ion tail calucation and for the crorsstalk) it should be
  checked one by one with currenlty used AliTPCDigitizer::DigitizeFast

 Modified version of the digitization function
 Modification: adding the ion tail and crosstalk:

 pcstream used in order to visually inspect data


 Crosstalk simulation:
   1.) Calculate per time bin mean charge (per pad)  within anode wire segment
   2.) Subsract for the clusters at given time bin fraction of (mean charge) normalized by add hoc constant
       AliTPCRecoParam::GetCrosstalkCorrection() (0 if not crosstalk, 1 if ideal crosstalk)
       for simplicity we are assuming that wire segents are related to pad-rows
       Wire segmentationn is obtatined from the
       AliTPCParam::GetWireSegment(Int_t sector, Int_t row); // to be implemented
       AliTPCParam::GetNPadsPerSegment(Int_t segmentID); // to be implemented
   3.) Substract form the signal contribution from the previous tracks - Ion tail in case speified in the AliTPCRecoParam
        AliTPCRecoParam::GetUseIonTailCorrection()

 Ion tail simulation:
    1.) Needs signal from pad+-1, taking signal from history
 merge input tree's with summable digits
 output stored in TreeTPCD