\Header{Exponential}{The Exponential Distribution}
\alias{dexp}{Exponential}
\alias{pexp}{Exponential}
\alias{qexp}{Exponential}
\alias{rexp}{Exponential}
\keyword{distribution}{Exponential}
\begin{Usage}
\begin{verbatim}
dexp(x, rate = 1)
pexp(q, rate = 1)
qexp(p, rate = 1)
rexp(n, rate = 1)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\texttt{x q}] vector of quantiles.
\item[\texttt{p}] vector of probabilities.
\item[\texttt{n}] number of observations to generate.
\item[\texttt{rate}] vector of rates.
\end{ldescription}
\end{Arguments}
\begin{Value}
These functions provide information about the exponential distribution
with rate \texttt{rate} (i.e., mean \texttt{1/rate}). 
\texttt{dexp} gives the density,
\texttt{pexp} gives the distribution function,
\texttt{qexp} gives the quantile function
and
\texttt{rexp} generates random deviates.

If \texttt{rate} is not specified, it assumes the default value of \texttt{1}.

The exponential distribution with rate \eqn{\lambda}{} has density
\deqn{
f(x) = \lambda {e}^{- \lambda x}}{f(x) = lambda e^(- lambda x)}
for \eqn{x \ge 0}{}.\end{Value}
\begin{SeeAlso}
\texttt{\Link{exp}} for the exponential function,
\texttt{\Link{dgamma}} for the gamma distribution and
\texttt{\Link{dweibull}} for the Weibull distribution, both of which
generalize the exponential.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
dexp(1) - exp(-1) #-> 0
r <- rexp(100)
all(abs(1 - dexp(1, r) / (r*exp(-r))) < 1e-14)
\end{ExampleCode}
\end{Examples}

