# [R] How do I modify uniroot function to return .0001 if error ?

eric ericstrom at aol.com
Sun Apr 3 22:12:31 CEST 2011

```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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```