[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,
>
>Sun
> [[alternative HTML version deleted]]
>
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Spencer Graves, PhD, Senior Development Engineer
O: (408)938-4420; mobile: (408)655-4567
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