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Last data update: 2014.03.03

R: Specify an Inflection-Point Category in a CHANGEPT Formula

ip	R Documentation

Specify an Inflection-Point Category in a CHANGEPT Formula

Description

A symbolic routine to define that the underlying mean curve has an inflection-point in the formula argument to changept.

Usage

ip(x, sh = 1)

Arguments

`x`	The predictor vector.
`sh`	If sh is 1, then the estimated curve is convex-concave; if sh is -1, it is concave-convex. Note that when the response is binomial or Poisson, sh is always 1. The default is sh = 1.

Value

The vector "x" with three attributes, i.e., nm: the name of x; categ: the category of the change-point, "inflect"; sh: the shape constraint on the estimated curve: 1 (convex-concave) or -1 (concave-convex).

The nm and categ attributes are used in the plot routine; the sh attribute is used to set up a shape-constrained regression.

Author(s)

Xiyue Liao

Examples

  # the underlying mean curve is a non-decreasing growth curve 
  # with an inflection point at .5 and it is convex-concave
  n = 100
  x = seq(1/n, 1, length = n)

  set.seed(123)
  y = 5 * (1 + tanh(10 * (x - .5)))  + rnorm(n, sd = 1)
  ans = changept(y ~ ip(x, sh = 1), fir = TRUE)

  plot(ans)

Results


R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

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> library(ShapeChange)
Loading required package: coneproj
Loading required package: quadprog
> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/ShapeChange/ip.Rd_%03d_medium.png", width=480, height=480)
> ### Name: ip
> ### Title: Specify an Inflection-Point Category in a CHANGEPT Formula
> ### Aliases: ip
> ### Keywords: symbolic routine
> 
> ### ** Examples
> 
>   # the underlying mean curve is a non-decreasing growth curve 
>   # with an inflection point at .5 and it is convex-concave
>   n = 100
>   x = seq(1/n, 1, length = n)
> 
>   set.seed(123)
>   y = 5 * (1 + tanh(10 * (x - .5)))  + rnorm(n, sd = 1)
>   ans = changept(y ~ ip(x, sh = 1), fir = TRUE)
> 
>   plot(ans)
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>