[R] uniroot
Thomas Subia
tg@77m @end|ng |rom y@hoo@com
Fri Aug 27 19:30:38 CEST 2021
Colleagues,
I've been using uniroot to identify a root of an equation.
As a check, I always verify that calculated root.
This is where I need some help.
Consider the following script
fun <- function(x) {x^x -23}
# Clearly the root lies somewhere between 2.75 and 3.00
uniroot(fun, lower = 2.75, upper = 3.00, tol = 0.001)
# output
$root
[1] 2.923125
$f.root
[1] 0.0001136763
# Let's verify this root.
2.923125^2.923125 - 23
0.0001222225
This result is different than what was calculated with uniroot
0.0001222225 # verified check using x = 2.923125
0.0001136763 # using $f.root
Does this imply that the root output of 2.923125 may need more significant
digits displayed?
I suspect that whatever root is calculated, that root may well be dependent
on what interval one defines where the root may occur
and what tolerance one has input.
I am not sure that is the case, nevertheless, it's worth asking the
question.
Some guidance would be appreciated.
Thanks!
Thomas Subia
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