class AliTrackerBase: public TObject

 The default constructor.

 The default constructor.

 Returns Bz (kG) at the point "r" .

 Returns Bx, By and Bz (kG) at the point "r" .

 Calculate mean material budget and material properties between
    the points "start" and "end".

 "mparam" - parameters used for the energy and multiple scattering
  corrections:

 mparam[0] - mean density: sum(x_i*rho_i)/sum(x_i) [g/cm3]
 mparam[1] - equivalent rad length fraction: sum(x_i/X0_i) [adimensional]
 mparam[2] - mean A: sum(x_i*A_i)/sum(x_i) [adimensional]
 mparam[3] - mean Z: sum(x_i*Z_i)/sum(x_i) [adimensional]
 mparam[4] - length: sum(x_i) [cm]
 mparam[5] - Z/A mean: sum(x_i*Z_i/A_i)/sum(x_i) [adimensional]
 mparam[6] - number of boundary crosses

  Origin:  Marian Ivanov, Marian.Ivanov@cern.ch

  Corrections and improvements by
        Andrea Dainese, Andrea.Dainese@lnl.infn.it,
        Andrei Gheata,  Andrei.Gheata@cern.ch

 Propagates the track to the plane X=xk (cm) using the magnetic field map
 and correcting for the crossed material.

 mass     - mass used in propagation - used for energy loss correction (if <0 then q = 2)
 maxStep  - maximal step for propagation

  Origin: Marian Ivanov,  Marian.Ivanov@cern.ch

 Propagates the track to the plane X=xk (cm) using the magnetic field map
 and correcting for the crossed material.

 mass     - mass used in propagation - used for energy loss correction
 maxStep  - maximal step for propagation

  Origin: Marian Ivanov,  Marian.Ivanov@cern.ch

 Propagates the track to the plane X=xk (cm)
 taking into account all the three components of the magnetic field
 and correcting for the crossed material.

 mass     - mass used in propagation - used for energy loss correction (if <0 then q=2)
 maxStep  - maximal step for propagation

  Origin: Marian Ivanov,  Marian.Ivanov@cern.ch

 This function brings the "track" with particle "mass" [GeV]
 to the same local coord. system and the same reference plane as
 of the "backup", doing it in "steps" [cm].
 Then, it calculates the 5D predicted Chi2 for these two tracks

 Initial approximation of the track curvature

 Initial approximation of the track snp

 Initial approximation of the tangent of the track dip angle

 Initial approximation of the tangent of the track dip angle

 Make Seed  - AliExternalTrackParam from input 3 points
 returning seed in local frame of point0

 refit the track  - trackParam using the points in point array

 Update track 1 with track 2