This is part of the analysis module

This can be used to output the data that has been stored in an Analysis object.

The most useful application of this method is to output all projections of all the points that were stored in an analysis object that performs some form of dimensionality reduction. If you use the USE_DIMRED_DATA_FROM option below projections of all the stored points will be output to a file. The positions of these projections will be calculated using that dimensionality reduction algorithms out-of-sample extension algorithm.

Glossary of keywords and components
The data to analyze can be the output from another analysis algorithm
USE_OUTPUT_DATA_FROM use the output of the analysis performed by this object as input to your new analysis object
Compulsory keywords
FILE the name of the file to output to
REPLICA ( default=0 ) the replicas for which you would like to output this information
STRIDE ( default=0 ) the frequency with which to perform the required analysis and to output the data. The default value of 0 tells plumed to use all the data
SERIAL ( default=off ) do the calculation in serial. Do not use MPI

( default=off ) lower the memory requirements

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...
FMT the format to output the data using