R help - Aug 2011 - 2-dim density plot

Hi All,

I have a 2-dim density defined on 0<x<1, 0<y<1, x<y. I know the
exact
formula of the density. How can I visualize it? What plot functions can I
use?

Thanks,
Annie

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I'd suggest either a color plot as given by image() and related functions or
a 3d mesh-plot which you can get from persp()

E.g.,

x = seq(0,1,by=0.01); y = x
z = outer(x,y+1,"/") # z = x/(y+1) -- I know that's not a density
but you
can adapt as necessary

filled.contour(x,y,z)
persp(x,y,z)

There are many more functions like this available, but here's a start.

Good luck!

Michael Weylandt

On Thu, Aug 11, 2011 at 3:11 PM, annie Zhang
<annie.zhang2010@gmail.com>wrote:
> Hi All,
>
> I have a 2-dim density defined on 0<x<1, 0<y<1, x<y. I know
the exact
> formula of the density. How can I visualize it? What plot functions can I
> use?
>
> Thanks,
> Annie
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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On 11/08/2011 3:11 PM, annie Zhang wrote:
> Hi All,
>
> I have a 2-dim density defined on 0<x<1, 0<y<1, x<y. I know
the exact
> formula of the density. How can I visualize it? What plot functions can I
> use?

persp() or contour() are in the graphics package.  There are similar 
ones in lattice (and I think in ggplot2), but I forget their names.  
There's also persp3d() in the rgl package for a rotatable version of 
persp().

Supposing f(x,y) gives the density at (x,y) (or NA if x > y), you plot 
it as follows:

x <- seq(0, 1, len=30)
y <- seq(0, 1, len=30)
z <- outer(x, y, f)
persp(x,y,z)
contour(x,y,z)
persp3d(x,y,z)

This relies on f() being vectorized; if it's not, use

z <- outer(x,y, Vectorize(f))

instead.

Duncan Murdoch