class AliRieman: public TObject

 default constructor

 default constructor

 copy constructor

 Destructor

 Reset all the data members

  Rieman update


 XY direction

  (x-x0)^2+(y-y0)^2-R^2=0 ===>

  (x^2+y^2 -2*x*x0 - 2*y*y0+ x0^2 -y0^2 -R^2 =0;  ==>

   substitution t = 1/(x^2+y^2),   u = 2*x*t, v = 2*y*t,  D0 = R^2 - x0^2- y0^2

  1 - u*x0 - v*y0 - t *D0 =0 ;  - linear equation

  next substition   a = 1/y0    b = -x0/y0   c = -D0/y0

  final linear equation :   a + u*b +t*c - v =0;

 Minimization :

 sum( (a + ui*b +ti*c - vi)^2)/(sigmai)^2 = min;

 where sigmai is the error of  maesurement  (a + ui*b +ti*c - vi)

 neglecting error of xi, and supposing  xi>>yi    sigmai ~ sigmaVi ~ 2*sigmay*t

  Rieman update

  Rieman update

 covariance matrices for rough extrapolation error estimate
 covariance matrix - get error estimates at point x = 0
 ! NOTE - error estimates is very rough and it is valid only if dl<<R
 when dl is the distance between first and last point

    P0'  = P0 + P1 * x +  P2 * x^2
    P1'  =      P1     +  P2 * x
    P2'  =             +  P2

    assumption error of curvature determination neggligible

    P0'  = P0 + P1 * x
    P1'  =      P1

 Get external parameters
 + approximative covariance
  0  1  2  3  4      // y   - local y
     5  6  7  8      // z   - local z
        9  10 11     // snp - local sin fi
           12 13     // tgl - deep angle
              14     // C   - curvature

 get y at given x position

 get dy/dx at given x position

 get z at given x position

 get dz/dx at given x postion

 Returns position given radius

 get curvature

 calculate chi2 for Y

 calculate chi2 for Z

 sum chi2 in both coord - supposing Y and Z independent

 create residual structure - ONLY for debug purposes