`fes` sums up hills using fast Bias Sum algorithm.
fes(hills, imin, imax, xlim, ylim, zlim, npoints)
hillsfile object.
index of a hill from which summation starts (default 1).
index of a hill from which summation stops (default the rest of hills).
numeric vector of length 2, giving the CV1 coordinates range.
numeric vector of length 2, giving the CV2 coordinates range.
numeric vector of length 2, giving the CV3 coordinates range.
resolution of the free energy surface in number of points.
fes object.