R help - Apr 2012 - Find position of asymptote

Hi all,

I would like to find the x position of an two asymptotes.

Here is a sample of what I would like to do:

x <- seq(1, 153,, 153)
a <- 85
m <- 65
s =-1.5
fn <- function (x, a, m, s) { a * (exp((m - x)/s) * (1/s))/((1 +
exp((m - x)/s)))^2 }
plot.deriv1 <- fn(1:153, a, m, s)

I can find the midpoint/minimum of this function easily. However, I
can not find the start and end of the two asymptote position (along
the x).
mid.point <- optimize(f=fn.sslogis.deriv1, interval=c(1:153), a=a,
m=m, s=s)$minimum

Thanks for your assistance,

Katrina

On Apr 19, 2012, at 4:41 AM, Katrina Bennett wrote:
> Hi all,
>
> I would like to find the x position of an two asymptotes.
>
> Here is a sample of what I would like to do:
>
> x <- seq(1, 153,, 153)
> a <- 85
> m <- 65
> s =-1.5
> fn <- function (x, a, m, s) { a * (exp((m - x)/s) * (1/s))/((1 +
> exp((m - x)/s)))^2 }
> plot.deriv1 <- fn(1:153, a, m, s)
>
> I can find the midpoint/minimum of this function easily. However, I
> can not find the start and end of the two asymptote position (along
> the x).
This is not a homework help-line.
> mid.point <- optimize(f=fn.sslogis.deriv1, interval=c(1:153), a=a,
> m=m, s=s)$minimum
>
> Thanks for your assistance,
>
> Katrina
-- 

David Winsemius, MD
West Hartford, CT