Hi all, I have a polynomial (a big one) and I would like to find a root of it between [-inf, -3] (it's known there is one root in this interval)... How to find that root? In using "uniroot" I need to supply the bounds.... In using "polyroot" I need to write it in the strict sens polynomial format... but I cannot... i.e. the polynomial is implicit... Thank you! [[alternative HTML version deleted]]
Petr Savicky
2012-Apr-19 17:03 UTC
[R] How to find a root for a polynomial between [-inf, -3]?
On Thu, Apr 19, 2012 at 08:59:34AM -0500, Michael wrote:> Hi all, > > I have a polynomial (a big one) and I would like to find a root of it > between [-inf, -3] (it's known there is one root in this interval)... > > How to find that root? > > In using "uniroot" I need to supply the bounds....Hi. Is the polynomial monotone in [-Inf, -3]? If it is, then it should not be too hard to find suitable bounds. An upper bound is -3. A lower bound may be derived analytically from the bounds on the coefficients, if you have some. Otherwise, derive a bound from the ranges of double values. The smallest negative double value is approximately -1.79e+308. The polynomial probably cannot be evaluated in this number, so use something smaller in absolute value, like -10^i, where i is something between 1 and 100. If the polynomial is not monotone in [-Inf, -3], which information on the polynomial you have, which implies that it has a root in this range? Petr Savicky.