# [R] plot multivariate function with known coefficient.

Gavin Simpson gavin.simpson at ucl.ac.uk
Wed Dec 10 12:35:28 CET 2008

```On Tue, 2008-12-09 at 16:07 -0800, YIHSU CHEN wrote:
> Dear R users --
>
> I have a simple question that I cannot find the answers in the archive
> email:  how to plot a multivariate function if I know the coefficients
> already?  For instance, if I like to plot a 3D fig of Pi against X and
> Y with the function Pi = a0 + a1X + a2Y, where a0, a1 & a2 are known.
> Can "curve" do this?  So far, I have only seen univariate case.

Not sure about a "curve3D()" but you can do this yourself using
expand.grid (to give combinations of X and Y you wish to evaluate Pi at)
and then use the vectorised nature of R to compute Pi for the
combinations given known coefficients.

E.g.:

X <- seq(1, 100, by = 5)
Y <- seq(1, 100, by = 5)
XY <- expand.grid(X = X, Y = Y)
a0 <- 2
a1 <- 0.5
a2 <- -0.3
Pi <- with(XY, a0 + (a1 * X) + (a2 * Y))
Pi <- matrix(Pi, ncol = length(X), byrow = TRUE)
persp(X, Y, Pi)

HTH

G

>
> Thank you.
>
> Yihsu Chen
>
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Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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