PRINT_NDX
This is part of the generic module

Print an ndx file

Examples
Glossary of keywords and components
The atoms involved can be specified using
ATOMS the list of atoms that have the corresponding arguments. For more information on how to specify lists of atoms see Groups and Virtual Atoms
Compulsory keywords
STRIDE ( default=1 ) the frequency with which the quantities of interest should be output
Options
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 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 Getting Started. Scalar values can also be referenced using POSIX regular expressions as detailed in the section on Regular Expressions. 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...
FILE the name of the file on which to output these quantities
LESS_THAN_OR_EQUAL when printing with arguments that are vectors only print components of vectors have a value less than or equal to this value
GREATER_THAN_OR_EQUAL when printing with arguments that are vectors only print components of vectors have a value greater than or equal to this value
RESTART allows per-action setting of restart (YES/NO/AUTO)
UPDATE_FROM Only update this action from this time
UPDATE_UNTIL Only update this action until this time