seglines {VGAM}

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, ...)

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.

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.

Value

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

Note

This function is likely to change in the short future because it is experimental and far from complete.

Author(s)

Thomas W. Yee.

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))
## Not run: 
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")

## End(Not run)