# seglines: Hauck-Donner Effects: Segmented Lines Plot In VGAM: Vector Generalized Linear and Additive Models

## Description

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

## Usage

 ```1 2 3 4 5 6 7 8``` ```seglines(x, y, dy, ddy, lwd = 2, cex = 2, plot.it = TRUE, add.legend = TRUE, position.legend = "topleft", 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"), tol0 = 0.1, 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`. `severity.table, tol0` 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. `FYI, ...` Should be ignored.

## Details

This function was written to complement `hdeffsev` and is rough-and-ready. It plots the 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.

`hdeff`, `hdeffsev`.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12``` ```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), myfun(xgrid, deriv = 2), position = "bottom") ## End(Not run) ```

### Example output ```Loading required package: stats4