R/interpol.r

In qpNCA: Noncompartmental Pharmacokinetic Analysis by qPharmetra

#' Interpolate Concentrations
#'
#' Interpolates concentrations.
#' Used by correct.xx functions to interpolate concentrations.
#' Uses linear interpolation unless method is 2 (log down), c1 > c2,
#' and both concentrations are non-zero.
#' @param c1 concentration 1 lagconc
#' @param c2 concentration 2 leadconc
#' @param t1 time 1 tiem where conc should be calculated
#' @param t2 time 2 lagtime
#' @param t3 time 3 leadtime
#' @param method calculation method (1, 2, or 3)
interpol <- function(c1=NA, c2=NA, t1=NA, t2=NA, t3=NA, method=1) {
  ifelse(
    method == 2 & c1>c2 & c1>0 & c2>0,
    exp(log(c1)+((log(c2)-log(c1))*(t1-t2)/(t3-t2))), # log down
    c1+((c2-c1)*(t1-t2)/(t3-t2))                      # lin or c1|c2==0
  )

}