When performing biased dynamics or analysing a trajectory you may wish to analyse/bias the value of some function of a set of collective variables rather than the values of the collective variables directly. You can do this with PLUMED by using any one of the following list of functions:

COMBINE	Calculate a polynomial combination of a set of other variables.
FUNCPATHMSD	This function calculates path collective variables.
FUNCSUMHILLS	This function is intended to be called by the command line tool sum_hills and it is meant to integrate a HILLS file or an HILLS file interpreted as a histogram i a variety of ways. Therefore it is not expected that you use this during your dynamics (it will crash!)
MATHEVAL	Calculate a combination of variables using a matheval expression.
PIECEWISE	Compute a piecewise straight line through its arguments that passes through a set of ordered control points.
SORT	This function can be used to sort colvars according to their magnitudes.
TARGET	This function measures the pythagorean distance from a particular structure measured in the space defined by some set of collective variables.