Add N particles

For adding more than four particles, either use QJADDP (see 10.3) or construct a loop with QVADDN:

      ISUM = KVNEW (DUMMY)
      DO 10 ITK = ... , ...
 10   CALL QVADDN (ISUM, ITK)

The sum of all track momenta is stored in ISUM.

Before using track ISUM in such loops, its momentum must be set to zero. This is done in KVNEW. When reusing ISUM for another loop, however, it must be zeroed by CALL QVZERO (ISUM).