evplot draws an “extreme-value plot”, i.e. a quantile-quantile plot
in which the horizontal axis is the quantile of an
extreme-value type I (Gumbel) distribution.
evdistp adds the cumulative distribution function of a distribution
to an extreme-value plot.
evdistq adds the quantile function of a distribution
to an extreme-value plot.
evpoints adds a set of data points to an extreme-value plot.
Numeric vector. The data values in the vector are plotted
on the extreme-value plot.
qfunc
A quantile function. The function is drawn as a curve
on the extreme-value plot.
pfunc
A cumulative distribution function. The function is drawn as a curve
on the extreme-value plot.
para
Distribution parameters for the quantile function qfunc
or cumulative distribution function pfunc.
If pfunc or qfunc is the standard R form of quantile function,
para should be a list.
If pfunc or qfunc is the qua... form
of quantile function used throughout the lmom package,
para should be a numeric vector.
In evplot, para is not used if qfunc is omitted.
npoints
Number of points to use in drawing the quantile function.
The points are equally spaced along the x axis.
Not used if qfunc is omitted.
plim
X axis limits, specified as probabilities.
xlim
X axis limits, specified as values of the Gumbel reduced variate
-log(-log(F)), where F is the
nonexceedance probability.
Not used if plim is specified.
ylim
Y axis limits.
type
Plot type. Determines how the data values in y are plotted.
Interpreted in the same way as argument type of function plot,
i.e. "p" for points, "b" for points connected by lines, etc.
xlab
X axis label.
ylab
Y axis label.
rp.axis
Logical. Whether to draw the “Return period” axis,
a secondary horizontal axis.
...
Additional arguments are passed to the plotting routine.
Arguments of cumulative distribution functions and quantile functions
pfunc and qfunc can be either the standard R form of
cumulative distribution function or quantile function
(i.e. for a distribution with r parameters, the first argument is the
variate x or the probability p and the next r arguments
are the parameters of the distribution) or the cdf... or
qua... forms used throughout the lmom package
(i.e. the first argument is the variate x or probability p
and the second argument is a vector containing the parameter values).
Note
Data points are plotted at the Gringorten plotting position,
i.e. the i'th smallest of n data points is plotted
at the horizontal position corresponding to nonexceedance probability
(i-0.44)/(n+0.12).
# Extreme-value plot of Ozone from the airquality data
data(airquality)
evplot(airquality$Ozone)
# Fit a GEV distribution and add it to the plot
evdistq(quagev, pelgev(samlmu(airquality$Ozone)))
# Not too good -- try a kappa distribution instead
evdistq(quakap, pelkap(samlmu(airquality$Ozone)), col="red")