VGAM (version 1.1-9)

seglines: Hauck-Donner Effects: Segmented Lines Plot

Description

Plots the piecewise segmented curve made up of Wald statistics versus estimates, using a colour code for the HDE severity.

Usage

seglines(x, y, dy, ddy, lwd = 2, cex = 2, plot.it = TRUE,
   add.legend = TRUE, cex.legend = 1,
   position.legend = "topleft", eta0 = NA, COPS0 = NA,
   lty.table = c("solid", "dashed", "solid", "dashed",
                 "solid", "dashed", "solid"),
   col.table = rainbow.sky[-5], pch.table = 7:1,
   severity.table = c("None", "Faint", "Weak", "Moderate",
   "Strong", "Extreme", "Undetermined"), FYI = FALSE, ...)

Value

This function returns the severity of the HDE, possibly invisibly.

Arguments

x, y, dy, ddy

Same as hdeffsev.

lwd, cex

Graphical parameters: line width, and character expansion.

plot.it

Logical, plot it? If FALSE then the other graphical arguments are ignored.

add.legend, position.legend

Logical and character; add a legend? The other argument is fed into legend.

cex.legend

Self-explanatory.

severity.table, eta0, COPS0

Same as hdeffsev.

lty.table, col.table, pch.table

Graphical parameters for the 7 different types of segments. Usually users should not assign anything to these arguments. Setting pch.table = NULL will suppress pch symbols from the legend.

FYI, ...

Should be ignored.

Author

Thomas W. Yee.

Details

This function was written to complement hdeffsev and is rough-and-ready. It plots the signed Wald statistics as a function of the estimates, and uses a colour-code to indicate the severity of the Hauck-Donner effect (HDE). This can be obtained from its first two derivatives.

See Also

hdeff, hdeffsev.

Examples

deg <- 4  # myfun is a function that approximates the HDE
myfun <- function(x, deriv = 0) switch(as.character(deriv),
  '0' = x^deg * exp(-x),
  '1' = (deg * x^(deg-1) - x^deg) * exp(-x),
  '2' = (deg * (deg-1) * x^(deg-2) - 2*deg * x^(deg-1) +
         x^deg) * exp(-x))
if (FALSE) {
curve(myfun, 0, 10, col = "white")
xgrid <- seq(0, 10, length = 101)
seglines(xgrid, myfun(xgrid), myfun(xgrid, deriv = 1),
         COPS0 = 2,
         myfun(xgrid, deriv = 2), pch.table = NULL,
         position = "bottom")
}