R: Extreme-value plot of a regional frequency distribution
evplot.rfd
R Documentation
Extreme-value plot of a regional frequency distribution
Description
Plots a regional frequency distribution, optionally with error bounds
for either the regional growth curve
or the quantile function for an individual site.
The graph is an “extreme-value plot”, i.e. the horizontal axis
is the quantile of an extreme-value type I (Gumbel) distribution,
and the quantile function of that distribution would plot as a straight line.
Object of class rfd, containing the specification
of a regional frequency distribution.
ybounds
Optional. Object of class rfdbounds (typically created
by regquantbounds or sitequantbounds),
containing error bounds for quantile estimates for the
regional frequency distribution specified by y.
npoints
Number of points to use in drawing the quantile function.
The points are equally spaced along the x axis.
add
Logical: if TRUE, add to existing plot.
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.
xlab
X axis label.
ylab
Y axis label.
rp.axis
Logical: whether to draw the “Return period” axis,
a secondary horizontal axis.
type
Vector of plot types. The first element is for the quantile
function; subsequent elements are for the error bounds,
and will be used cyclically until all lines are drawn.
Interpreted in the same way as the type plotting parameter,
i.e. "l" for lines, "b" for points connected by lines, etc.
lty
Vector of line types. The first element is for the quantile
function; subsequent elements are for the error bounds,
and will be used cyclically until all lines are drawn.
col
Vector of colors. The first element is for the quantile
function; subsequent elements are for the error bounds,
and will be used cyclically until all lines are drawn.
...
Additional parameters are passed to the plotting routine.
Details
If ybounds is missing, a graph is drawn of the quantile function
(regional growth curve) of the distribution specified by y.
If ybounds is present, it may contain error bounds for either
a regional growth curve or the quantile function at a single site.
This regional growth curve or site quantile function is plotted
using arguments type[1], lty[1] and col[1].
Then, in each case, error bounds are added to the plot.
The ybounds object typically contains,
for several probabilities specified by ybounds$bounds,
error bounds corresponding to that probability
for several quantiles.
For thejth bound probability, the bounds for the various quantiles
will be joined by straight lines (so to obtain a smooth curve
there should be a lot of quantiles!), using graphics parameters
type[j+1], lty[j+1] and col[j+1].
regfit, which creates objects of class "rfd";
regquantbounds and sitequantbounds,
which create objects of class "rfdbounds";
evdistp, evdistq, and evpoints,
all in package lmom, for adding further curves and points
to the plot.
Examples
Cascades # An object of class "regdata"
rfit <- regfit(Cascades, "gno") # Fit a generalized normal distribution
evplot(rfit) # Plot the regional growth curve
# Compute error bounds for quantile estimates. We will
# (optimistically) generate bounds for a homogeneous region
# with the same frequency distribution as the one fitted to
# the Cascades data.
fval <- seq(.01, .99, by=.01) # A lot of quantiles
simq <- regsimq(rfit$qfunc, nrec=Cascades$n, nrep=100, f=fval,
fit=rfit$dist)
# Regional growth curve, and bounds
rbounds <- regquantbounds(simq, rfit)
evplot(rfit, rbounds)
# Quantile function for site 3, and bounds
sbounds <- sitequantbounds(simq, rfit, site=3)
evplot(rfit, sbounds)