R/parlap.R

In lmomco: L-Moments, Censored L-Moments, Trimmed L-Moments, L-Comoments, and Many Distributions

"parlap" <-
function(lmom,checklmom=TRUE,...) {

    para <- rep(NA,2)
    names(para) <- c("xi","alpha")
    if(length(lmom$lambdas) == 0) { # convert to named L-moments
      lmom <- lmorph(lmom)     # nondestructive conversion!
    }
    if(checklmom & ! are.lmom.valid(lmom)) {
       warning("L-moments are invalid")
       return()
    }

    L1 <- lmom$lambdas[1]
    L2 <- lmom$lambdas[2]
    L3 <- lmom$lambdas[3]
    L4 <- lmom$lambdas[4]

    para[1] <- L1 - (50/31)*L3 # Hosking (1986), IBM RC12210 # 54860, p. 57.
    para[2] <- 1.4741*L2 - 0.5960*L4

    return(list(type = 'lap', para = para, source="parlap"))
}