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Short helpfile for action CLUSTER_DIAMETER
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The following arguments are compulsory: 

               CLUSTERS - the label of the action that does the clustering 
                CLUSTER - ( default=1 ) which cluster would you like to look at 1 is 
                          the largest cluster, 2 is the second largest, 3 is the the 
                          third largest and so on. 

In addition you may use the following options: 

  NUMERICAL_DERIVATIVES - ( default=off ) calculate the derivatives for these 
                          quantities numerically 
                  NOPBC - ( default=off ) ignore the periodic boundary conditions 
                          when calculating distances 
                 SERIAL - ( default=off ) do the calculation in serial. Do not use 
                          MPI 
                 LOWMEM - ( default=off ) lower the memory requirements 
                TIMINGS - ( default=off ) output information on the timings of the 
                          various parts of the calculation 

