[R] optimize

[David Winsemius]

On Jan 3, 2011, at 9:52 AM, Muhammad Rahiz wrote:

> Hi all,
>
> I'm trying to get the value of y when x=203 by using the intersect  
> of three curves. The horizontal curve does not meet with the other  
> two. How can I rectify the code below?

Extend the appropriate axes. xlim and ylim are the arguments to use.  
Looks too much like a homework problem for me to do the work for you,  
though.

>
> Thanks
>
> Muhammad
>
> ts <- 1:10
> dd <- 10:1
>
> ts <- seq(200,209,1)
> dd <- c(NA,NA,NA,NA,1.87,1.83,1.86,NA,1.95,1.96)
>
> plot(ts,dd,ylim=c(1.5,2))
> abline(lm(dd~ts),col="blue",lty=2)
> abline(v=203,col="blue",lty=2)
>
> xy <- lm(dd~ts)
> fc <- function(x) coef(xy)[1] + x*coef(xy)[2]
> val <- optimize(f=function(x) abs(fc(x)-203),c(1.5,2))
> abline(h=val,col="blue",lty=2)
>

David Winsemius, MD
West Hartford, CT