[R] Info

[Andrea Calandra]

Sorry

I'm student in biomedical engineer and i have to solve this formula
for immuno-assay. I need to design a calibration curve

But i don't understand How can i write this formula in R language:
y = a + (c - a) /(1+ e[-b(x-m])

where
x = ln(analyte dose + 1)
y = the optical absorbance data
a = the curves top asymptote
b = the slope of the curve
c = the curves bottom asymptote
m = the curve X intercept

I have to calculate the parameters (a,b,c,m).After with X that i know
i calculate the Y.


i try:


yeld.fit <- nls( y ~ a + (c.-a)/(1+exp(-b*(x-m))),
 data = yeld,
 start = list( a= 0, c.=2, b= 1, m=4 ),
 trace = TRUE )


where yeld is a data.frame
  x y
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5


but give me an error: << exceeded number of itwerations>>

thank you
Andrea