actuar (version 0.9-3)

InverseWeibull: The Inverse Weibull Distribution

Description

Density, distribution function, quantile function, random generation, raw moments and limited moments for the Inverse Weibull distribution with parameters shape and scale.

Usage

dinvweibull(x, shape, rate = 1, scale = 1/rate, log = FALSE)
  pinvweibull(q, shape, rate = 1, scale = 1/rate,
              lower.tail = TRUE, log.p = FALSE)
  qinvweibull(p, shape, rate = 1, scale = 1/rate,
              lower.tail = TRUE, log.p = FALSE)
  rinvweibull(n, shape, rate = 1, scale = 1/rate)
  minvweibull(order, shape, rate = 1, scale = 1/rate)
  levinvweibull(limit, shape, rate = 1, scale = 1/rate,
                order = 1)

Arguments

x, q

vector of quantiles.

p

vector of probabilities.

n

number of observations. If length(n) > 1, the length is taken to be the number required.

shape, scale

parameters. Must be strictly positive.

rate

an alternative way to specify the scale.

log, log.p

logical; if TRUE, probabilities/densities $p$ are returned as $\log(p)$.

lower.tail

logical; if TRUE (default), probabilities are $P[X \le x]$, otherwise, $P[X > x]$.

order

order of the moment.

limit

limit of the loss variable.

Value

• dinvweibull gives the density, pinvweibull gives the distribution function, qinvweibull gives the quantile function, rinvweibull generates random deviates, minvweibull gives the $k$th raw moment, and levinvweibull gives the $k$th moment of the limited loss variable.

  Invalid arguments will result in return value NaN, with a warning.

Details

The Inverse Weibull distribution with parameters shape $= \tau$ and scale $= \theta$ has density: $$f(x) = \frac{\tau (\theta/x)^\tau e^{-(\theta/x)^\tau}}{x}$$ for $x > 0$, $\tau > 0$ and $\theta > 0$.

The special case shape == 1 is an Inverse Exponential distribution.

The $k$th raw moment of the random variable $X$ is $E[X^k]$ and the $k$ limited moment at some limit $d$ is $E[\min(X, d)]$.

References

Klugman, S. A., Panjer, H. H. and Willmot, G. E. (2004), Loss Models, From Data to Decisions, Second Edition, Wiley.

Examples

exp(dinvweibull(2, 3, 4, log = TRUE))
p <- (1:10)/10
pinvweibull(qinvweibull(p, 2, 3), 2, 3)
mlgompertz(-1, 3, 3)
levinvweibull(10, 2, 3, order = 2)