How to draw the graph of f(x,y) = x * y ?

You could always try
 F(x,y) = f(x) + 0*y

That is "zero out" the degenerate dimensions.  Of course you'll be
plotting what is essentially a two dimensional object as if it were
three dimensional.  The degeneracy in y means a 2-D curve will be
"extruded" along the Y dimension.

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Paul Smith
Sent: Wednesday, September 24, 2008 06:20
To: r-help at stat.math.ethz.ch
Subject: Re: [R] How to draw the graph of f(x,y) = x * y ?

On Wed, Sep 24, 2008 at 4:05 AM, Ben Bolker <bolker at ufl.edu> wrote:

The function curve() draws the graph of functions from R to R. Is
there some homologous function to curve() to draw functions from R^2
to R?

 There is a curve3d function in the emdbook package on CRAN.

Thanks, Ben and Robin. I think curve3d should be included in the base
of R. It would help many users, I believe.

I do not know whether curve3d could be extended to draw constant
functions and functions like f(x,y) = x. With the current version, I
get the following:

curve3d(1)

Error in curve3d(1) :
 'expr' must be a function or an expression containing 'x' and 'y'

curve3d(x)

Error in eval(expr, envir, enclos) : could not find function "x"