curve {graphics}R Documentation

Draw Function Plots


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


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, ...)


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


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.


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=""))

[Package graphics version 2.5.0 Index]