There is one obvious way:
> test <- function(x, value = 0) {
a <- x[1]
b <- x[2]
ex <- if (all(x > 0))
(((a/(a+b))*(beta(a,b)/(beta(a,b)-beta(a,b+6))))-0.35259)
else Inf
(ex - value)^2
}
> opt <- optim(c(1,2),test)
>
> opt[c("par", "value")]
$par
[1] 0.5141272 2.4810257
$value
[1] 2.613923e-17
>
> originalTest <- function(x) {
a <- x[1]
b <- x[2]
if (all(x > 0))
(((a/(a+b))*(beta(a,b)/(beta(a,b)-beta(a,b+6))))-0.35259)
else Inf
}
>
> with(opt, originalTest(par))
[1] -5.112654e-09
Not bad.
Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
AUSTRALIA
Office Phone (email preferred): +61 7 3826 7251
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mailto:[EMAIL PROTECTED]
http://www.cmis.csiro.au/bill.venables/
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of francogrex
Sent: Sunday, 16 March 2008 3:24 AM
To: r-help@r-project.org
Subject: [R] Solving equations with optim
Hello, optim searches for min (or max) of a function, but is it possible
to
solve for a specific value? I mean, I want to find the value of a and b
that
give the function value closest to ZERO (and not min or max) in the
below.
is it possible? thanks
test=function(x){
a=x[1]
b=x[2]
if (all(x>0))(((a/(a+b))*(beta(a,b)/(beta(a,b)-beta(a,b+6))))-0.35259)
else Inf
}
optim(c(1,2),test)
--
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
