This is part of the generic module

Print quantities to a file.

This directive can be used multiple times in the input so you can print files with different strides or print different quantities to different files. You can control the buffering of output using the FLUSH keyword. Output file is either appended or backed up depending on the presence of the RESTART action. A per-action RESTART keyword can be used as well.

Notice that printing happens in the so-called "update" phase. This implies that printing is affected by the presence of UPDATE_IF actions. In addition, one might decide to start and stop printing at preassigned values of time using the UPDATE_FROM and UPDATE_UNTIL keywords. Keep into account that even on steps when the action is not updated (and thus the file is not printed) the argument will be activated. In other words, if you use UPDATE_FROM to start printing at a given time, the collective variables this PRINT statement depends on will be computed also before that time.

Examples

The following input instructs plumed to print the distance between atoms 3 and 5 on a file called COLVAR every 10 steps, and the distance and total energy on a file called COLVAR_ALL every 1000 steps.

Click on the labels of the actions for more information on what each action computes

# compute distance:
distance: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. 
=2,5 The DISTANCE action with label distance calculates a single scalar value
# compute total energy (potential)
energy: ENERGY The ENERGY action with label energy calculates a single scalar value
# print distance on a file
PRINT ARGthe input for this action is the scalar output from one or more other actions. 
=distance STRIDEcompulsory keyword ( default=1 )
the frequency with which the quantities of interest should be output 
=10 FILEthe name of the file on which to output these quantities 
=COLVAR The PRINT action with label 
# print both variables on another file
PRINT ARGthe input for this action is the scalar output from one or more other actions. 
=distance,energy STRIDEcompulsory keyword ( default=1 )
the frequency with which the quantities of interest should be output 
=1000 FILEthe name of the file on which to output these quantities 
=COLVAR_ALL The PRINT action with label

Notice that DISTANCE and ENERGY are computed respectively every 10 and 1000 steps, that is only when required.

Glossary of keywords and components

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
FMT	the format that should be used to output real numbers
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