Hi:

This is pure speculation since you didn't provide a minimal data set to test
this with, but is it possible that theta is meant to be a parameter
*vector*? If so, then you should have

eta <- theta[1]
K <- theta[2]

The code theta[, 1] means that you want to extract the first column of the
_matrix_ theta. More below.

On Tue, Aug 3, 2010 at 2:44 PM, 楠 程 <jnjushi@yahoo.com.cn> wrote:

> Hi,
> How to solve this problem. The following is the code.
>
> betabinexch0=function(theta,data)
> + {
> + eta=theta[,1]
> + K=theta[,2]
> + y=data[,1]; n=data[,2]
> + N=length(y)
> + val=0*K;
>
+ for (i in 1:N)
> + val=val+lbeta(K*eta+y[i],K*(1-eta)+n[i]-y[i])
>

This indicates that n[i] and y[i] are scalars, but as you have it defined,
K*eta is a vector and so is K * (1 - eta). That's capable of causing
dimension problems.


> + val=val-N*lbeta(K*eta,K*(1-eta))
>

N * lbeta(K * eta, K * (1 - eta)) will yield a vector given the way you
defined K and eta.

+ val=val-2*log(1+K)-log(eta)-log(1-eta)   # Again, this part yields a
> vector.
> + return(val)
> + }
> > data(cancermortality)
> > mycontour(betabinexch0,c(.0001,.003,1,20000),cancermortality)
>

If eta and K are meant to be scalars, then the loop is unnecessary as you
can do everything using vectorized arithmetic, which in turn means that the
code should run faster.

Here's a modification, assuming theta is a vector rather than a matrix:

betabinexch0=function(theta,data)
 {
eta=theta[1]
K=theta[2]
y=data[,1]; n=data[,2]
N=length(y)
# val=0*K;
# for (i in 1:N)
val= lbeta(rep(K*eta, N) + y, rep(K*(1-eta), N) + n - y)
       - rep(N * lbeta(K*eta,K*(1-eta)), N)
       - rep(2*log(1+K)-log(eta)-log(1-eta), N)
ifelse(!any(is.nan(val)), sum(val), NaN)
 }

# The rep(whatever, N) trick is a cheap way of expanding a scalar into a
vector. (There are others...)

# Create some fake data and call the function:
d <- data.frame(y = rpois(10, 5), n = rpois(10, 10))
theta <- c(0.5, 10)

betabinexch0(theta, d)   # example
[1]  -127.1016

It is possible for the function to yield Inf or NaN as its result, so you
have to be careful about the inputs.

How this plays into your mycontour call I have no idea. I would expect that
the betabinexch0 argument would have at least an () at the end, if not two
arguments within parentheses, but again, without seeing what mycontour looks
like, it's hard to say.

HTH,
Dennis

Error in theta[, 1] : incorrect number of dimensions
>
>
>
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