class AliTPCSpaceCharge3D: public AliTPCCorrection

 default constructor

 default destructor

 Initialization funtion

 Update function

 Calculates the correction due the Space Charge effect within the TPC drift volume

 Initialization of the Lookup table which contains the solutions of the
 "space charge" (poisson) problem - Faster and more accureate

 Method: Weighted sum-up of the different fields within the look up table
 but using two lookup tables with higher granularity in the (r,z) and the (rphi)- plane to emulate
 more realistic space charges. (r,z) from primary ionisation. (rphi) for possible Gating leaks

 Initialization of the Lookup table which contains the solutions of the
 "space charge" (poisson) problem

 The sum-up uses a look-up table which contains different discretized Space charge fields
 in order to calculate the corresponding field deviations due to a given (discretized)
 space charge distribution ....

 Method of calculation: Weighted sum-up of the different fields within the look up table
 Note: Full 3d version: Course and slow ...

 Set & load the Space charge density distribution from a file
 (linear interpolation onto a standard grid)

 Use 3D space charge map as an optional input
 The layout of the input histogram is assumed to be: (phi,r,z)
 Density histogram is expreseed is expected to bin in  C/m^3

 Standard histogram interpolation is used in order to use the density at center of voxel

 returns the (input) space charge density at a given point according
 Note: input in [cm], output in [C/m^3/e0] !!

 return a simple histogramm containing the space charge distribution (input for the calculation)

 return a simple histogramm containing the space charge distribution (input for the calculation)

 Example on how to write a Space charge distribution into a File
  (see below: estimate from scaling STAR measurements to Alice)
 Charge distribution is splitted into two (RZ and RPHI) in order to speed up
 the needed calculation time

 Print function to check the settings of the boundary vectors
 option=="a" prints the C0 and C1 coefficents for calibration purposes

 MI extension  - calculate E field
               - inspired by  AliTPCROCVoltError3D::InitROCVoltError3D()
 Initialization of the Lookup table which contains the solutions of the
 Dirichlet boundary problem
 Calculation of the single 3D-Poisson solver is done just if needed
 (see basic lookup tables in header file)

 Origin: Christian Lippmann, CERN, Christian.Lippmann@cern.ch based on the internal note (xxx ...)
 adopted by Marian Ivanov (different epsilon in IROC and OROC)

 Charge distribution is splitted into two (RZ and RPHI) in order to speed up
 the needed calculation time.

 Explanation of variables:
 1) multiplicity: charghed particle dn/deta for top 80% centrality (660 for 2011,
    expect 950 for full energy)
 2) intRate: Total interaction rate (e.g. 50kHz for the upgrade)
 3) eps: Number of backdrifting ions per primary electron (0 for MWPC, e.g.10 for GEM)
 4) gasfactor: Use different gas. E.g. Ar/CO2 has twice the primary ionization, ion drift
    velocity factor 2.5 slower, so  gasfactor = 5.

 some grid, not too coarse

 common setters and getters for tangled ExB effect

 setters and getters