4.4.57 SUBROUTINE ZTTRWT(INCR, IERR) : calc. TRacK WeiGhT matrix

This routine follows a track stored in /ZTSTA/ through the detector geometry stored in /ZTBAR/ and/or /FORWARD/ and calculates track parameters and their weight and covariance matrices on a surface stored in /ZTSEL/.

ARGUMENTS:

INPUT :

    INCR : TRUE : transport the input weight matrix in /MATRIX/ along the
           track. Else : build the matrix from scratch.

OUTPUT :

    IERR : error flag :
             0 - no error
             2 - track turns back before reference surface

IMPLICIT INPUTS:

    from /ZTSTA/ : PMOM, THETA, PHI0 and AMASS : momentum direction and
                    mass of particle at vertex ; ZVRTX : z-position of vertex;
                    BFIELD : magnetic field [T].
    from /ZTTRJ/ : IREF : the type of reference surface (1 = cylinder,
                  2 = plane).

IMPLICIT OUTPUTS:

    from /ZTAUX/ : COTTH,TANTH : Cot and tan (theta) of track;
                 RTRK,RINV : radius of track, and it's inverse;
                 BCONST : c*BFIELD; PINV : inverse of momentum;

CALLED BY :

ZTERRM (see 4.4.2).

CALLED ROUTINE(S):

ZTWGTC (see 4.4.62)

(To calculate weight matrix.)

ZTMINV

(To invert weight matrix.)

SIDE EFFECTS:

none

AUTHORS:

P. Billoir , LPNHE

CREATION DATE:

27-jul-1992