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Short helpfile for action ECV_CUSTOM
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The following arguments are compulsory: 

                   TEMP - ( default=-1 ) temperature. If not specified tries to get 
                          it from MD engine 
                    ARG - the labels of the single ECVs, \f$\Delta U_i\f$, in energy 
                          units 

In addition you may use the following options: 

  NUMERICAL_DERIVATIVES - ( default=off ) calculate the derivatives for these 
                          quantities numerically 
                 ADD_P0 - ( default=off ) add the unbiased Boltzmann distribution to 
                          the target distribution, to make sure to sample it 
          DIMENSIONLESS - ( default=off ) consider ARG as dimensionless rather than 
                          an energy, thus do not multiply it by \f$\beta\f$ 
                BARRIER - a guess of the free energy barrier to be overcome (better 
                          to stay higher than lower) 


