R: Draw Function Plots

curve {graphics}

R Documentation

Draw Function Plots

Description

Draws a curve corresponding to the given function or, for curve() also an expression (in x) over the interval [from,to].

Usage

curve(expr, from = NULL, to = NULL, n = 101, add = FALSE,
      type = "l", ylab = NULL, log = NULL, xlim = NULL, ...)

## S3 method for class 'function'
plot(x, y = 0, to = 1, from = y, xlim = NULL, ...)

Arguments

expr

an expression written as a function of x, or alternatively the name of a function which will be plotted.

x

a ‘vectorizing’ numeric R function.

from, to

the range over which the function will be plotted.

n

integer; the number of x values at which to evaluate.

add

logical; if TRUE add to already existing plot.

xlim

numeric of length 2; if specified, it serves as default for c(from, to).

type

plot type: see plot.default.

y

alias for from for compatibility with plot()

ylab, log, ...

labels and graphical parameters can also be specified as arguments. plot.function passes all these to curve.

Details

The evaluation of expr is at n points equally spaced over the range [from, to], possibly adapted to log scale. The points determined in this way are then joined with straight lines. x(t) or expr (with x inside) must return a numeric of the same length as the argument t or x.

For curve(), if either of from or to is NULL, it defaults to the corresponding element of xlim, and xlim defaults to the x-limits of the current plot. For plot(<function>, ..), the defaults for (from,to) are (0,1).

log is taken from the current plot only when add is true, and otherwise defaults to "" indicating linear scales on both axes.

This used to be a quick hack which now seems to serve a useful purpose, but can give bad results for functions which are not smooth.

For expensive-to-compute expressions, you should use smarter tools.

Examples

plot(qnorm)
plot(qlogis, main = "The Inverse Logit : qlogis()")
abline(h=0, v=0:2/2, lty=3, col="gray")

curve(sin, -2*pi, 2*pi)
curve(tan, main = "curve(tan)  --> same x-scale as previous plot")

op <- par(mfrow=c(2,2))
curve(x^3-3*x, -2, 2)
curve(x^2-2, add = TRUE, col = "violet")

## simple and sophisticated, quite similar:
plot(cos, -pi,  3*pi)
plot(cos, xlim = c(-pi,3*pi), n = 1001, col = "blue", add=TRUE)

chippy <- function(x) sin(cos(x)*exp(-x/2))
curve(chippy, -8, 7, n=2001)
plot (chippy, -8, -5)

for(ll in c("","x","y","xy"))
   curve(log(1+x), 1,100, log=ll, sub=paste("log= '",ll,"'",sep=""))
par(op)