[R] how to draw a multivariate function

Sun sun at cae.wisc.edu
Sun Oct 17 06:31:26 CEST 2004

```Thanks, Spencer. Turing it into a function seems really to make difference.

Well but I don't know what is the difference between

data1 = cbind (x, y, f(x,y))
cloud(data1)

and

cloud(f(x,y) ~ x *y)?

They draw different plots. I don't know which one is correct. I am really
confused.

Here are codes:
n = 30
lamdaa = 4
lamdab = 1.5

pa = lamdaa/n
pb = lamdab/n

x <- seq(0, n/2, len = n/2+1)
y <- seq(0, n/2, len = n/2+1)
f <- function(x,y) (factorial(n)/
(factorial(x) * factorial(y) * factorial(n-x-y))*
pa^x * pb^y * ((1-pa-pb)^(n-x-y)))

data1 = cbind (x, y, f(x,y))
cloud(data1)

cloud(f(x,y) ~ x *y)

------------------------

Thanks a lot
----- Original Message -----
From: "Spencer Graves" <spencer.graves at pdf.com>
To: "Sun" <sun at cae.wisc.edu>
Cc: "R-help mailing list" <R-help at stat.math.ethz.ch>
Sent: Saturday, October 16, 2004 11:06 PM
Subject: Re: [R] how to draw a multivariate function

>       Have you studied the documentation for "wireframe" including the
> examples?  See also the contour plot examples in Venables and Ripley
> (2002) Modern Applied Statistics with S, 4th ed. (Springer).
>
>       It might help if you write your function as follows:
>
> f <- function(x,y ,n, pa, pb) (factorial(n)/
>      (factorial(x) * factorial(y) * factorial(n-x-y))*
>                       pa^x * pb^y * ((1-pa-pb)^(n-x-y)))
>
>       I hope this fills in enough gaps that you will be able to complete
> the remaining steps.
>
>       Good luck.  spencer graves
>
> Sun wrote:
>
> >Hi, Rusers:
> >
> >Thanks for answering my last questions. I am frustrated in plotting a
trinomial pmf function
> >
> >f(x,y | n, pa, pb) = factorial(n)/ (factorial(x) * factorial(y) *
factorial (n-x-y))* pa^x * pb^y * ((1-pa-pb)^(n-x-y))
> >
> >obviously it is a bivariate function of x and y. But I have put a lot of
time on this.
> >
> >**********************************
> >x <- seq(0, n, len = n/2+1) # for now I set it to n/2 to control x+y <= n
> >y <- seq(0, n, len = n/2+1)
> >f = factorial(n)/ (factorial(x) * factorial(y) * factorial (n-x-y))* pa^x
* pb^y * ((1-pa-pb)^(n-x-y))
> >wireframe(f ~ x * y, shade = TRUE)
> >**********************************
> >
> >well, but it plots nothing out.
> >
> >I wonder if you could help me? Seems R is hard to learn without your
help.
> >
> >Many thanks,
> >
> >Sun
> > [[alternative HTML version deleted]]
> >
> >______________________________________________
> >R-help at stat.math.ethz.ch mailing list
> >https://stat.ethz.ch/mailman/listinfo/r-help
http://www.R-project.org/posting-guide.html
> >
> >
>
> --
> Spencer Graves, PhD, Senior Development Engineer
> O:  (408)938-4420;  mobile:  (408)655-4567
>
>
>

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