R help - Apr 2011 - How do I modify uniroot function to return .0001 if error ?

I am calling the uniroot function from inside another function using these
lines (last two lines of the function) :

d <- uniroot(k, c(.001, 250), tol=.05)
return(d$root)

The problem is that on occasion there's a problem with the values I'm
passing to uniroot. In those instances uniroot stops and sends a message
that it can't calculate the root because f.upper * f.lower is greater than
zero.  All I'd like to do in those cases is be able to set the return value
of my calling function "return(d$root)" to .0001. But I'm not sure
how to
pull that off. I tried a few modifications to uniroot but so far no luck.

For convenience, the uniroot function is shown below:

uniroot <- function (f, interval, ..., lower = min(interval), upper
max(interval),
    f.lower = f(lower, ...), f.upper = f(upper, ...), tol
.Machine$double.eps^0.25,
    maxiter = 1000) 
{
    if (!missing(interval) && length(interval) != 2L) 
        stop("'interval' must be a vector of length 2")
    if (!is.numeric(lower) || !is.numeric(upper) || lower >= 
        upper) 
        stop("lower < upper  is not fulfilled")
    if (is.na(f.lower)) 
        stop("f.lower = f(lower) is NA")
    if (is.na(f.upper)) 
        stop("f.upper = f(upper) is NA")
    if (f.lower * f.upper > 0)
        stop("f.up * f.down > 0")
    val <- .Internal(zeroin2(function(arg) f(arg, ...), lower, 
        upper, f.lower, f.upper, tol, as.integer(maxiter)))
    iter <- as.integer(val[2L])
    if (iter < 0) {
        warning("_NOT_ converged in ", maxiter, "
iterations")
        iter <- maxiter
    }
    list(root = val[1L], f.root = f(val[1L], ...), iter = iter, 
        estim.prec = val[3L])
}

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eric <ericstrom <at> aol.com> writes:
> 
> I am calling the uniroot function from inside another function using these
> lines (last two lines of the function) :
> 
> d <- uniroot(k, c(.001, 250), tol=.05)
> return(d$root)
> 
> The problem is that on occasion there's a problem with the values
I'm
> passing to uniroot. In those instances uniroot stops and sends a message
> that it can't calculate the root because f.upper * f.lower is greater
than
> zero.  All I'd like to do in those cases is be able to set the return
value
> of my calling function "return(d$root)" to .0001. But I'm not
sure how to
> pull that off. I tried a few modifications to uniroot but so far no luck.
> 
Do not modify uniroot(). Use 'try' or 'tryCatch', for example

    	e <- try( d <- uniroot(k, c(.001, 250), tol=.05), silent = TRUE )
	if (class(e) == "try-error") {
		return(0.0001)
	} else {
		return(d$root)	
	}

--Hans Werner