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Short helpfile for action PDB2CONSTANT
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The following arguments are compulsory: 

              REFERENCE - a file in pdb format containing the reference structure 
                 NUMBER - ( default=0 ) if there are multiple structures in the pdb 
                          file you can specify that you want the RMSD from a specific 
                          structure by specifying its place in the file here. If NUMBER=0 then 
                          the RMSD from all structures are computed 

In addition you may use the following options: 

                 NOARGS - ( default=off ) the arguments that are being read from the 
                          PDB file are not in the plumed input 
                    ARG - read this single argument from the input rather than the 
                          atomic structure 


