Draws a curve corresponding to a function over the interval
[from, to]. curve can plot also an expression in the variable
xname, default x.
curve(expr, from = NULL, to = NULL, n = 101, add = FALSE,
type = "l", xname = "x", xlab = xname, ylab = NULL,
log = NULL, xlim = NULL, …)# S3 method for function
plot(x, y = 0, to = 1, from = y, xlim = NULL, ylab = NULL, …)
The name of a function, or a call or an
expression written as a function of x which will
evaluate to an object of the same length as x.
a ‘vectorizing’ numeric R function.
alias for from for compatibility with plot
the range over which the function will be plotted.
integer; the number of x values at which to evaluate.
logical; if TRUE add to an already existing plot; if
NA start a new plot taking the defaults for the limits and
log-scaling of the x-axis from the previous plot. Taken as
FALSE (with a warning if a different value is supplied) if no
graphics device is open.
NULL or a numeric vector of length 2;
if non-NULL it provides the defaults for c(from, to)
and, unless add = TRUE, selects the x-limits of the plot -- see
plot.window.
plot type: see plot.default.
character string giving the name to be used for the x axis.
labels and graphical parameters
can also be specified as arguments. See ‘Details’ for the
interpretation of the default for log.
For the "function" method of plot, … can
include any of the other arguments of curve, except
expr.
A list with components x and y of the points that were
drawn is returned invisibly.
For historical reasons, add is allowed as an argument to the
"function" method of plot, but its behaviour may surprise
you. It is recommended to use add only with curve.
The function or expression expr (for curve) or function
x (for plot) is evaluated at n points equally
spaced over the range [from, to]. The points determined in
this way are then plotted.
If either from or to is NULL, it defaults to the
corresponding element of xlim if that is not NULL.
What happens when neither from/to nor xlim
specifies both x-limits is a complex story. For
plot(<function>) and for curve(add = FALSE) the defaults
are \((0, 1)\). For curve(add = NA) and curve(add =
TRUE) the defaults are taken from the x-limits used for the previous
plot. (This differs from versions of R prior to 2.14.0.)
The value of log is used both to specify the plot axes (unless
add = TRUE) and how ‘equally spaced’ is interpreted: if
the x component indicates log-scaling, the points at which the
expression or function is plotted are equally spaced on log scale.
The default value of log is taken from the current plot when
add = TRUE, whereas if add = NA the x component is taken
from the existing plot (if any) and the y component defaults to
linear. For add = FALSE the default is ""
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.
The way curve handles expr has caused confusion. It
first looks to see if expr is a name (also known as a
symbol), in which case it is taken to be the name of a function, and
expr is replaced by a call to expr with a single
argument with name given by xname. Otherwise it checks that
expr is either a call or an expression, and that
it contains a reference to the variable given by xname (using
all.vars): anything else is an error. Then expr
is evaluated in an environment which supplies a vector of name given
by xname of length n, and should evaluate to an object
of length n. Note that this means that curve(x, ...) is
taken as a request to plot a function named x (and it is used
as such in the function method for plot).
The plot method can be called directly as plot.function.
# NOT RUN {
plot(qnorm) # default range c(0, 1) is appropriate here,
# but end values are -/+Inf and so are omitted.
plot(qlogis, main = "The Inverse Logit : qlogis()")
abline(h = 0, v = 0:2/2, lty = 3, col = "gray")
curve(sin, -2*pi, 2*pi, xname = "t")
curve(tan, xname = "t", add = NA,
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 advanced versions, quite similar:
plot(cos, -pi, 3*pi)
curve(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 = paste0("log = '", ll, "'"))
par(op)
# }