R/pglo.R

In sbegueria/SPEI: Calculation of the Standardized Precipitation-Evapotranspiration Index

# Cumulative distribution function of the Generalized Logistic probability
# distribution function.
#
pglo <-
  function(x, para) {
    if (!are.parglo.valid(para)) {
      return()
    }
    SMALL <- 1e-15
    XI <- para$para[1]
    A <- para$para[2]
    K <- para$para[3]
    f <- vector(mode = "numeric")
    for (i in seq(1, length(x))) {
      if (is.na(x[i])) {
        f[i] <- NA
        next
      }
      Y <- (x[i] - XI) / A
      if (K == 0) {
        f[i] <- 1 / (1 + exp(-Y))
        next
      }
      ARG <- 1 - K * Y
      if (ARG > SMALL) {
        Y <- -log(ARG) / K
        f[i] <- 1 / (1 + exp(-Y))
        next
      }
      if (K < 0) {
        f[i] <- 0
        next
      }
      if (K > 0) {
        f[i] <- 1
        next
      }
      warning("Should not be here in execution")
    } # next i
    return(f)
  }