Hi Jeff,
Thanks for the reply. I am aware that the sign needs to be different at
the ends of the starting interval.
Another question:
Is there a way to set the right end point ( (the "upper" argument in the
uniroot function below) as the point where the function takes on its
minimun, for example my function f1 below?
Thanks very much!
u1 <- -3
u2 <- 4
pi0 <- 0.8
f1 <- function(lambda,z,p1){
lambda*(p1*exp(u1*z-u1^2/2)+(0.2-p1)*exp(u2*z-u2^2/2))-(1-lambda)*pi0}
x <- seq(-20,20, by=0.1)
y <- numeric(length(x))
for (i in 1:length(x)){y[i] <- f1(x[i],p1=0.15,lambda=0.998)}
plot(y ~ x, ylim=c(-1,1))
abline(h=0)
a <- uniroot(f1, lower =-10, upper = 0,
tol = 1e-20,p1=0.15,lambda=0.998)$root
2015-04-15 22:57 GMT-04:00 Jeff Newmiller <jdnew...@dcn.davis.ca.us>:
> You really need to read the help page for uniroot. The sign needs to be
> different at the ends of the starting interval. This is a typical
> limitation of numerical root finders.
> ---------------------------------------------------------------------------
> Jeff Newmiller The ..... ..... Go Live...
> DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live
> Go...
> Live: OO#.. Dead: OO#.. Playing
> Research Engineer (Solar/Batteries O.O#. #.O#. with
> /Software/Embedded Controllers) .OO#. .OO#. rocks...1k
> ---------------------------------------------------------------------------
> Sent from my phone. Please excuse my brevity.
>
> On April 15, 2015 7:20:04 PM PDT, li li <hannah....@gmail.com> wrote:
> >Hi all,
> >In the following code, I am trying to use uniroot function to solve for
> >the root (a and b in code below) for function f1.
> >I am not sure why uniroot function does not give the answer since when
> >we
> >look the graph, the function does cross 0 twice.
> >Any suggestion?
> > Thanks.
> > Hanna
> >
> >u1 <- -3
> >u2 <- 4
> >pi0 <- 0.8
> >
> >f1 <- function(lambda,z,p1){
> >lambda*(p1*exp(u1*z-u1^2/2)+(0.2-p1)*exp(u2*z-u2^2/2))-(1-lambda)*pi0}
> >
> >a <- uniroot(f1, lower =-10, upper = 0,
> > tol = 1e-20,p1=0.15,lambda=0.998)$root
> >
> >b <- uniroot(f1, lower =0, upper = 10,
> > tol = 1e-20,p1=0.15,lambda=0.998)$root
> >
> >x <- seq(-20,20, by=0.1)
> >y <- numeric(length(x))
> >for (i in 1:length(x)){y[i] <- f1(x[i],p1=0.15,lambda=0.998)}
> >plot(y ~ x, ylim=c(-1,1))
> >abline(h=0)
> >
> > [[alternative HTML version deleted]]
> >
> >______________________________________________
> >R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >https://stat.ethz.ch/mailman/listinfo/r-help
> >PLEASE do read the posting guide
> >http://www.R-project.org/posting-guide.html
> <http://www.r-project.org/posting-guide.html>
> >and provide commented, minimal, self-contained, reproducible code.
>
>
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
