Estimates the roughness exponent from the HHCF from spline fit.

This function will return NA if the HHFC is monotically increasing.

get_alpha_(row, dr, xi, do_plot = FALSE)

Arguments

row	array of hhcf values
dr	numeric, spacing of the values along the axis
xi	numeric, auto-correlation length
do_plot	logical, plot the fit, default to FALSE