[R] how to draw a multivariate function

Spencer Graves spencer.graves at pdf.com
Sun Oct 17 06:06:39 CEST 2004

      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,
>	[[alternative HTML version deleted]]
>R-help at stat.math.ethz.ch mailing list
>PLEASE do read the posting guide! 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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