curve {graphics}R Documentation

Draw Function Plots

Description

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

Usage

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

## S3 method for class 'function':
plot(x, from = 0, to = 1, 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, ylab, log, ... 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.

If add = TRUE, c(from,to) default to xlim which defaults to the current x-limits. Further, log is taken from the current plot when add is true.

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” expressions, you should use smarter tools.

See Also

splinefun for spline interpolation, lines.

Examples

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

plot(cos, xlim = c(-pi,3*pi), n = 1001, col = "blue")

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