This is part of the gridtools module

Interpolate a smooth function stored on a grid onto a grid with a smaller grid spacing.

This action takes a function evaluated on a grid as input and can be used to interpolate the values of that function on to a finer grained grid. The interpolation within this algorithm is done using splines.

Examples

The input below can be used to post process a trajectory. It calculates a HISTOGRAM as a function the distance between atoms 1 and 2 using kernel density estimation. During the calculation the values of the kernels are evaluated at 100 points on a uniform grid between 0.0 and 3.0. Prior to outputting this function at the end of the simulation this function is interpolated onto a finer grid of 200 points between 0.0 and 3.0.

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

x: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. 
=1,2  You cannot view the components that are calculated by each action for this input file. Sorry 
hA1: HISTOGRAM ARGthe quantity that is being averaged 
=x GRID_MINcompulsory keyword ( default=auto )
the lower bounds for the grid 
=0.0 GRID_MAXcompulsory keyword ( default=auto )
the upper bounds for the grid 
=3.0 GRID_BINthe number of bins for the grid 
=100 BANDWIDTHthe bandwidths for kernel density esimtation 
=0.1  You cannot view the components that are calculated by each action for this input file. Sorry 
ii: INTERPOLATE_GRID GRID could not find this keyword 
=hA1 GRID_BINthe number of bins for the grid 
=200  You cannot view the components that are calculated by each action for this input file. Sorry 
DUMPGRID GRIDthe grid you would like to print (can also use ARG for specifying what is being printed)
=ii FILEcompulsory keyword ( default=density )
the file on which to write the grid. 
=histo.dat  You cannot view the components that are calculated by each action for this input file. Sorry

Glossary of keywords and components

Compulsory keywords

INTERPOLATION_TYPE

( default=spline ) the method to use for interpolation. Can be spline, linear, ceiling or floor.

Options

SERIAL	( default=off ) do the calculation in serial. Do not parallelize
MIDPOINTS	( default=off ) interpolate the values of the function at the midpoints of the grid coordinates of the input grid
ZERO_OUTSIDE_GRID_RANGE	( default=off ) if we are asked to evaluate the function for a number that is outside the range of the grid set it to zero
GRID_BIN	the number of bins for the grid
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...
GRID_SPACING	the approximate grid spacing (to be used as an alternative or together with GRID_BIN)