plot.wd: Plot Method for a `wd' object

Description

Plot wavelet coefficients of an object of class "wd".

Usage

## S3 method for class 'wd':
plot(wd, xlabels, first.level = 1,
     main = "Wavelet Decomposition Coefficients",
     sub = wd$filter$name,
     xlab = "Translate", ylab = "Resolution Level",
     scaling="by.level", rhlab = FALSE, \dots)

Arguments

object of class "wd", containing a wavelet decomposition of a function.

xlabels

if supplied, this argument should be a vector containing the x-axis for the plot. For example, if you are trying to regress y on x, then you might want to put "x" in as the x-axis. Otherwise, the translates will be plotted.

first.level

integer, determining how many of the low resolution levels are plotted. The default, first.level=1 means that 1 coefficient is plotted.

main, sub, xlab, ylab

main and sub-title, x- and y- axis label of plot

scaling

type of scaling applied to levels within the plot. Either "by.level" or "global".

rhlab

logical; determines whether the scale factors applied to each level before plotting are printed as the right hand axis.

...

other arguments to be supplied to plot.wd, see plot.

Value

Axis labels to the right of the picture. These values are the maximum of the absolute value of the coefficients at that resolution level. They are returned because they are sometimes hard to read on the plot.

Side Effects

A plot of the wavelet coefficients at each resolution level is produced.

RELEASE

Details

The picture produced is similar to those in Donoho and Johnstone 1992. Wavelet coefficients for each resolution level are plotted one above the other, with the high resolution coefficients at the bottom, and the low resolution at the top. The coefficients are plotted using the "segment" function, with a large positive coefficient being plotted above an imaginary horizontal centre line, and a large negative coefficient plotted below it. The position of a coefficient along a line is indicative of the wavelet basis function's translate number.

The resolution levels are labelled on the left-hand side axis, and the maximum values of the absolute values of the coefficients for the particular level form the right-hand side axis.

The levels of coefficients can be scaled in two ways. If you are not interested in comparing the relative scales of coefficients from different levels, then the default "scaling" option, "by.level" is what you need. This computes the maximum of the absolute value of the coefficients at a particular level and scales the so that the fit nicely onto the plot. For this option, each level is scaled DIFFERENTLY. To obtain a uniform scale for all the levels specify the "global" option to the "scaling" argument. This will allow you to make inter-level comparisons.