*
*
*               COMMON2 variables
*               *****************
*
*       ---------------------------------------------------------------------
*       ALPHA   Density contrast factor (NNBMAX*sqrt(0.08*RSCALE**3/N)).
*       BE      Total energy (=1: initial; =2: previous; =3: current).
*       BODY    Mass of an individual body.
*       BODY1   Maximum particle mass.
*       BODYM   Average particle mass.
*       CGAS    Scale factor for logarithmic potential (KZ(15) = 2).
*       CMR     Centre of mass coordinates and scalar value.
*       CMRDOT  Centre of mass velocity and scalar value.
*       CPU     Maximum computing time in minutes.
*       CPU0    Elapsed computing time at last output.
*       CPUTOT  Total computing time (including previous runs).
*       D1      First divided difference of the irregular force.
*       D1R     First divided difference of the regular force.
*       D2      Second divided difference of the irregular force.
*       D2R     Second divided difference of the regular force.
*       D3      Third divided difference of the irregular force.
*       D3R     Third divided difference of the regular force.
*       DELTAT  Time interval for output.
*       DTLIST  Time interval for updating the time-step list.
*       EPS2    Softening distance squared.
*       ERRTOT  Accumulated sum of relative energy errors (DE/E).
*       ETA0    Initial value of irregular time-step parameter.
*       ETAI    Time-step parameter for the irregular force polynomial.
*       ETAR    Time-step parameter for the regular force polynomial.
*       F       One-half the total force on a particle.
*       FDOT    One-sixth the total force derivative on a particle.
*       FI      Irregular force due to neighbours.
*       FR      Regular force due to distant particles.
*       ICOMP   Index of first merger component.
*       ILIST   Temporary neighbour list array.
*       IPHASE  Flow control indicator for decision-making.
*       JCOMP   Index of second merger component.
*       JLIST   Temporary array for sorting and working space.
*       KZ      Options for alternative paths at run time.
*       LIST    Neighbour list (LIST(1,I) = membership).
*       LMAX    Maximum size of neighbour list (PARAMETER).
*       MODEL   Model identification index (option 3; frequency NFIX).
*       N       Total particle number.
*       NAME    Initial particle name.
*       NBCORR  Force polynomial corrections.
*       NBFULL  Too many neighbours with standard criterion.
*       NBVOID  No neighbours inside 1.26 of basic sphere radius.
*       NC      Number of particles inside the core radius.
*       NDUMP   Automatic restart counter (maximum 2 restarts; option 2).
*       NESC    Number of escaped particles (option 13).
*       NFIX    Output frequency for optional data bank or binary search.
*       NLIST   Time-step list for determining next body to be advanced.
*       NMAX    Maximum size of particle arrays (PARAMETER).
*       NMERG   Inelastic mergers (option 12).
*       NMTRY   Merger attempts.
*       NNBMAX  Maximum number of neighbours.
*       NNPRED  Full N coordinate predictions.
*       NPRINT  Output counter (reset to zero when NPRINT = NFIX).
*       NRUN    Run identification index.
*       NSTEPI  Irregular integration steps.
*       NSTEPR  Regular integration steps.
*       NSTEPS  Time-step counter for COMMON save (100*NMAX steps; KZ(1) >1).
*       NTIMER  Time-step counter for checking elapsed cpu time.
*       ONE12   The constant 1.0/12.0.
*       ONE3    The constant 1.0/3.0.
*       ONE6    The constant 1.0/6.0.
*       ONE9    The constant 1.0/9.0.
*       POT     Total potential energy at output time (positive).
*       QE      Relative energy tolerance for error control.
*       RBAR    Virial cluster radius in pc (assumed = 1 if zero input).
*       RC      Core radius (generalized Casertano-Hut algorithm; option 8).
*       RC2     Square core radius.
*       RDENS   Density centre (Casertano-Hut algorithm).
*       RGAS    Scale factor for logarithmic potential (KZ(15) = 2).
*       RHOD    Average core density (scaled by mean density).
*       RHOM    Maximum core density (scaled by mean density).
*       RS      Radius of the neighbour sphere.
*       RSCALE  Half-mass radius (from potential energy or Lagrange radii).
*       RSMIN   Minimum neighbour radius since last output.
*       RTIDE   Tidal radius (2*RTIDE for escaper removal; option 13).
*       STAB1   Lower stabilization limit for time-step list interval.
*       STAB2   Upper stabilization limit for time-step list interval.
*       STEP    Time-step for an irregular force polynomial.
*       STEPR   Time-step for a regular force polynomial.
*       T0      Time of last irregular force calculation.
*       T0R     Time of last regular force calculation.
*       T1      Time of first backwards irregular force calculation.
*       T1R     Time of first backwards regular force calculation.
*       T2      Time of second backwards irregular force calculation.
*       T2R     Time of second backwards regular force calculation.
*       T3      Time of third backwards irregular force calculation.
*       T3R     Time of third backwards regular force calculation.
*       TCR     Standard crossing time (from total mass and energy).
*       TCR0    Initial crossing time (2*sqrt(2) in standard units).
*       TCRIT   Termination time in scaled units.
*       TIME    Physical integration time in scaled units.
*       TLIST   Time for next updating of the time-step list.
*       TNEXT   Time for next output.
*       TSTAR   Time unit for scaling to 10**6 yrs.
*       VC      Root mean square velocity in the core.
*       VIR     Total virial energy (= POT with no softening).
*       VSTAR   Velocity unit for scaling to km/sec.
*       X       Coordinates of a particle at current time.
*       X0      Coordinates at the beginning of a step.
*       X0DOT   Velocities at the beginning of a step.
*       XDOT    Velocities at beginning of step and at output time.
*       XTPAR   Mass & square softening for external potential (KZ(15) = 1).
*       ZKIN    Total kinetic energy at output time.
*       ZMASS   Current total mass (initial value = 1 in standard units).
*       ZMBAR   Mean stellar mass in solar masses.
*       ZMC     Core mass.
*       ZMGAS   Mass scale for logarithmic potential (KZ(15) = 2).
*       ZNBMAX  Maximum predicted neighbour number.
*       ZNBMIN  Minimum predicted neighbour number.
*       ---------------------------------------------------------------------
*
