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Short helpfile for action HISTOGRAM
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The following arguments are compulsory: 

                 STRIDE - ( default=1 ) the frequency with which the data should be 
                          collected and added to the quantity being averaged 
                  CLEAR - ( default=0 ) the frequency with which to clear all the 
                          accumulated data. The default value of 0 implies that all the data will 
                          be used and that the grid will never be cleared 
              BANDWIDTH - the bandwidths for kernel density estimation 
                 KERNEL - ( default=gaussian ) the kernel function you are using. 
                          More details on the kernels available in plumed plumed can be 
                          found in \ref kernelfunctions. 
          NORMALIZATION - ( default=ndata ) This controls how the data is normalized 
                          it can be set equal to true, false or ndata. See above for an 
                          explanation 
               GRID_MIN - the lower bounds for the grid 
               GRID_MAX - the upper bounds for the grid 

In addition you may use the following options: 

                 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 
             LOGWEIGHTS - list of actions that calculates log weights that should be 
                          used to weight configurations when calculating averages 
          CONCENTRATION - the concentration parameter for Von Mises-Fisher 
                          distributions 
                    ARG - the input for this action is the scalar output from one or 
                          more other actions. The particular scalars that you will use are 
                          referenced using the label of the action. If the label appears on its 
                          own then it is assumed that the Action calculates a single 
                          scalar value. The value of this scalar is thus used as the input 
                          to this new action. If * or *.* appears the scalars calculated 
                          by all the proceeding actions in the input file are taken. 
                          Some actions have multi-component outputs and each component of 
                          the output has a specific label. For example a \ref DISTANCE 
                          action labelled dist may have three components x, y and z. To take 
                          just the x component you should use dist.x, if you wish to take 
                          all three components then use dist.*.More information on the 
                          referencing of Actions can be found in the section of the manual on the 
                          PLUMED \ref Syntax. Scalar values can also be referenced using 
                          POSIX regular expressions as detailed in the section on \ref 
                          Regex. To use this feature you you must compile PLUMED with the 
                          appropriate flag.. You can use multiple instances of this keyword i.e. 
                          ARG1, ARG2, ARG3... 
                   DATA - input data from action with vessel and compute histogram 
                VECTORS - input three dimensional vectors for computing histogram 
               GRID_BIN - the number of bins for the grid 
           GRID_SPACING - the approximate grid spacing (to be used as an alternative 
                          or together with GRID_BIN) 
            UPDATE_FROM - Only update this action from this time 
           UPDATE_UNTIL - Only update this action until this time 


