[R] plotting curve in xYplot -- using panel.curve

[John Poulsen]

Hello,

I am trying to plot a curve over points plotted with se's in xYplot (see 
example below).  I can get Figure 1 below to plot the data with error.  
However, I keep getting a the error message

"Error using packet 1 object "y" not found"

Can anyone see what I am doing wrong?

Thanks!
John

-------------------------------

 a=0.002; b=31.7; c=0.51
 sds=rep(c(0,3,5,10,20,50,200), each=3)
 y1=c(0,0,0.16, 0, 0.33,0.5, 0.16, 0.83, 1.16, 0.67, 0.5, 1.16, 0.83, 
2.33, 3.6, 5.5, 4.33, 1.16, 22, 13, 12)
 lo=y1-0.1*y1
 hi=y1+0.1*y1
 
# Figure 1
 xYplot(Cbind(y1, lo, hi)~jitter(sds, amount=1), 
method="bars",ylim=c(0,max(hi)+1),
       ylab="Y", xlab="X")

# Figure 2
 xYplot(Cbind(y1, lo, hi)~jitter(sds, amount=1), 
method="bars",ylim=c(0,max(hi)+1),
       ylab="Y", xlab="X",
     panel=function(...){
      panel.xYplot(x,y,...)
      panel.number=panel.number()
       panel.curve(curve(a*(x+c)/1+a*b*(x+c), from=0, type="l", lwd=2))
        }
         )