# persp3d.function

##### Plot a function of two variables

Plot a function `z(x, y)`

or a parametric function
`(x(s, t), y(s, t), z(s, t))`

.

- Keywords
- graphics

##### Usage

```
# S3 method for function
persp3d(x,
xlim = c(0, 1), ylim = c(0, 1),
slim = NULL, tlim = NULL,
n = 101,
xvals = seq.int(min(xlim), max(xlim), length.out = n[1]),
yvals = seq.int(min(ylim), max(ylim), length.out = n[2]),
svals = seq.int(min(slim), max(slim), length.out = n[1]),
tvals = seq.int(min(tlim), max(tlim), length.out = n[2]),
xlab, ylab, zlab,
col = "gray", otherargs = list(),
normal = NULL, texcoords = NULL, …)
# S3 method for function
plot3d(x, …)
```

##### Arguments

- x
A function of two arguments. See the details below.

- xlim, ylim
By default, the range of x and y values. For a parametric surface, if these are not missing, they are used as limits on the displayed x and y values.

- slim, tlim
If not

`NULL`

, these give the range of s and t in the parametric specification of the surface. If only one is given, the other defaults to`c(0, 1)`

.- n
A one or two element vector giving the number of steps in the x and y (or s and t) grid.

- xvals, yvals
The values at which to evaluate x and y. Ignored for a parametric surface. If used,

`xlim`

and/or`ylim`

are ignored.- svals, tvals
The values at which to evaluate s and t for a parametric surface. Only used if

`slim`

or`tlim`

is not`NULL`

. As with`xvals`

and`yvals`

, these override the corresponding`slim`

or`tlim`

specification.- xlab, ylab, zlab
The axis labels. See the details below for the defaults.

- col
The color to use for the plot. See the details below.

- otherargs
Additional arguments to pass to the function.

- normal, texcoords
Functions to set surface normals or texture coordinates. See the details below.

- …
Additional arguments to pass to

`persp3d`

.

##### Details

The `"function"`

method for `plot3d`

simply passes
all arguments to `persp3d`

. Thus this description applies
to both.

The first argument `x`

is required to be a function. It
is named `x`

only because of the requirements of the S3
system; in the remainder of this help page, we will assume
that the assignment `f <- x`

has been made, and will
refer to the function `f()`

.

`persp3d.function`

evaluates `f()`

on a two-dimensional
grid of values, and displays the resulting surface. The values
on the grid will be passed in as vectors in the
first two arguments to the function, so `f()`

needs
to be vectorized. Other optional arguments to `f()`

can be specified in the `otherargs`

list.

In the default form where `slim`

and `tlim`

are both
`NULL`

, it is assumed that `f(x, y)`

returns heights,
which will be plotted in the z coordinate. The default axis labels
will be taken from the argument names to `f()`

and the
expression passed as argument `x`

to this function.

If `slim`

or `tlim`

is specified, a parametric
surface is plotted. The function
`f(s, t)`

must return a 3-column matrix, giving x, y and z
coordinates of points on the surface. The default axis
labels will be the column names if those are present.
In this case `xlim`

, `ylim`

and `zlim`

are used to define a clipping region only if specified;
the defaults are ignored.

The color of the surface may be specified as the name of a color, or a vector or matrix of color names. In this case the colors will be recycled across the points on the grid of values.

Alternatively, a function may be given: it should be a function
like `rainbow`

that takes an integer argument and
returns a vector of colors. In this case the colors are mapped
to z values.

The `normal`

argument allows specification of a function
to compute normal vectors to the surface. This function is
passed the same arguments as `f()`

(incuding `otherargs`

if present), and should produce a 3-column matrix containing the
x, y and z coordinates of the normals.

The `texcoords`

argument is a function similar to `normal`

, but
it produces a 2-column matrix containing texture coordinates.

Both `normal`

and `texcoords`

may also contain matrices,
with 3 and 2 columns respectively, and rows corresponding to the
points that were passed to `f()`

.

##### Value

This function constructs a call to `persp3d`

and returns the value from that function.

##### See Also

The `curve`

function in base graphics does
something similar for functions of one variable. See the
example below for space curves.

##### Examples

```
# NOT RUN {
# (1) The Obligatory Mathematical surface.
# Rotated sinc function, with colors
f <- function(x, y) {
r <- sqrt(x^2 + y^2)
ifelse(r == 0, 10, 10 * sin(r)/r)
}
open3d()
plot3d(f, col = colorRampPalette(c("blue", "white", "red")),
xlab = "X", ylab = "Y", zlab = "Sinc( r )",
xlim = c(-10, 10), ylim = c(-10, 10),
aspect = c(1, 1, 0.5))
# (2) A cylindrical plot
f <- function(s, t) {
r <- 1 + exp( -pmin( (s - t)^2,
(s - t - 1)^2,
(s - t + 1)^2 )/0.01 )
cbind(r*cos(t*2*pi), r*sin(t*2*pi), s)
}
open3d()
plot3d(f, slim = c(0, 1), tlim = c(0, 1), col = "red", alpha = 0.8)
# Add a curve to the plot, fixing s at 0.5.
plot3d(f(0.5, seq.int(0, 1, length.out = 100)), type = "l", add = TRUE,
lwd = 3, depth_test = "lequal")
# }
```

*Documentation reproduced from package rgl, version 0.100.50, License: GPL*