R: Draw Function Plots

curve {base} | 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, ...)
    plot(x, from = 0, to = 1, xlim = NULL, ...)

### Arguments

`expr` | an expression written as a function of `x`, or alternatively 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'' `expr`essions, 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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