In newer versions of R (I have 3.6 and previously had 3.2), the stats::regularize.values function has been changed to have a default value of warn.collapsing as TRUE. This function is used in splinefun and several other interpolation functions in R. In a microsimulation model, I am using splinefun to smooth a large amount (n > 100,000) of data points of the form (x, f(x)). Here, x is a simulated vector of positive-valued scalers, and f(x) is some function of …