============
                                     LIBTRK
                                    (R-1.01)
                                  ============

LIBTRK is a library containing fortran subroutines of general utility. 
The library is stored in the directory trk-software-ground/bin. Both a static
(.a) and dynamic (.so) libraries have been created. 

List of subroutines
-------------------

- TRACK
- READ_B
- INTER_B


Usage:

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CALL READ_B
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Read the magnetic field maps (rz files) and fill related common blocks.
===> To be called once, before using TRACK and INTER_B

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CALL TRACK(*NPTOF,*ZIN,XOUT*,YOUT*,*AL_P,IFAIL*)
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NPTOF         (INTEGER) Num. points 
ZIN(NPTOF)    (DOUBLE) Input z-coordinates (in cm)
XOUT(NPTOF)   (DOUBLE) Output x-coordinates (in cm)
YOUT(NPTOF)   (DOUBLE) Output y-coordinates (in cm)
AL_P(6)       (DOUBLE) Track state vector
IFAIL         (INTEGER) Error flag (ok if IFLAG=0)

Calculate particle-trajectory coordinates, for the state vector AL_P, 
at z-coordinates set by the user. 
(Make use of GRKUTA, routine to solve kinematic equations in a magnetic field
using Runge-Kutta method, adapted from GEANT3 library)

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CALL INTER_B(*X,*Y,*Z,B*)
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X,Y,Z         (DOUBLE) Coordinates (in m)
B(3)          (DOUBLE) Magnetic field (in T)

Evaluate the three components of the magnetic field, by interpolating the
measured magnetic field map. 
(Used by TRACK)