On 22-01-2012, at 19:25, Eliano wrote:
> People,
>
> I'm researching some Bayesian statistic topics and in the midle of my study
> i found a very simple problem and i'm trying to find a simple package to
> solve this type of equations:
>
> Lets say that i need to compute beta values for the beta distribution and i
> now for example:
>
> E(teta)=a/(a+b) = 0,5
> Var(teta)=ab/((a+b)^2(a+b+1))=0.05
>
> So if i want to solve this to non-linear system to find a,b for the beta
> distribution wich pack should i use?
>
> I know that a=2 and b=2 because i calculated it.
>
There is a package nleqslv which can handle you system.
library(nleqslv)
eqf <- function(x) {
a <- x[1]
b <- x[2]
y <- numeric(2)
y[1] <- a/(a+b) - 0.5
y[2] <- a*b/((a+b)^2 * (a+b+1)) -0.05
y
}
x.start <- c(1,1)
nleqslv(x.start,eqf)
Berend
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