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CERN Program Library Long Writeup W5013 - CERNLIB ...

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CALL GRKUTA<br />

(CHARGE,STEP,VECT,VOUT*)<br />

The arguments have the same meaning than those of GHELIX. Transport a particle in magnetic field using<br />

Runge-Kutta method for solving the kinematic equations (Nystroem algorithm [1], procedure 25.5.20). The<br />

call to this routine is selected by GUSWIM when IFIELD=1 in the call to GSTMED. This method is the slower<br />

of the three and it must be used for magnetic fields with strong gradient. Again the magnetic field is obtained<br />

from the GUFLD routine which the user has to code.<br />

CALL GUFLD<br />

((VECT,F*)<br />

VECT<br />

F<br />

(REAL) array of 3 with the position in space where the field has to be returned;<br />

(REAL) array of 3 with the magnetic field in VECT, in kilo-Gauss units.<br />

User routine to return the three components of the magnetic field at point VECT expressed in kilo-Gauss.<br />

This routine must be provided by the user for all tracking media where IFIELD is 1 or 2. This routine will<br />

be called very often, at least three times at each step, so all the care must be put in its optimisation.<br />

TRAK500 – 2 351

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