BRIDGE
This is part of the adjmat module
It is only available if you configure PLUMED with ./configure –enable-modules=adjmat . Furthermore, this feature is still being developed so take care when using it and report any problems on the mailing list.

Calculate a matrix with elements equal to one if there is a bridging atom between the two atoms

Examples
Glossary of keywords and components
The atoms involved can be specified using
GROUP the atoms for which you would like to calculate the adjacency matrix. For more information on how to specify lists of atoms see Groups and Virtual Atoms
GROUPA . For more information on how to specify lists of atoms see Groups and Virtual Atoms
GROUPB . For more information on how to specify lists of atoms see Groups and Virtual Atoms
BRIDGING_ATOMS The list of atoms that can form the bridge between the two interesting parts of the structure.. For more information on how to specify lists of atoms see Groups and Virtual Atoms
Options
SWITCH The parameters of the two switchingfunction in the above formula
SWITCHA The switchingfunction on the distance between bridging atoms and the atoms in group A
SWITCHB The switchingfunction on the distance between the bridging atoms and the atoms in group B