OptionalextendExtend the interval when f has the same sign at both ends: "yes" (both ways), "downX" (f decreasing),
"upX" (f increasing) or "no" (default). A unique prefix is accepted and anything else is an error, as in R.
Optionalff(lower), when already known.
Optionalff(upper), when already known.
OptionalmaxiterMaximum number of iterations. Default 1000.
OptionaltolAccuracy. Default eps^0.25.
Options for uniroot.