[R] question with uniroot function

Carl Witthoft
Mon, 05 Sep 2011 00:23:04 -0000

As others will tell you: you need to provide a reproducible example.
What are p1, u1, u2 ?

<quote>
Dear all,

    I have the following problem with the uniroot function. I want to
find roots for the fucntion "Fp2" which is defined as below.

Fz <- function(z){0.8*pnorm(z)+p1*pnorm(z-u1)+(0.2-p1)*pnorm(z-u2)}

Fp <- function(t){(1-Fz(abs(qnorm(1-(t/2)))))+(Fz(-abs(qnorm(1-(t/2)))))}

Fp2 <- function(t) {Fp(t)-0.8*t/alpha}

th <- uniroot(Fp2, lower =0, upper =1,

            tol = 0.0001)$root

The result is 0 as shown below.

 > th

[1] 0

However, there should be a root between 0.00952 and 0.00955, since the
function values are of opposite signs as below.

 > Fp2(0.00952)

[1] 2.264272e-05
 > Fp2(0.00955)

[1] -0.0003657404

Can any one give me a hand here? Thanks a lot.

        Hannah
--
-----
Sent from my Cray XK6