[R] Info

[Spencer Graves]

	  Thanks for providing data and sample command.  (In the future, please 
provide the data in the form of a "data.frame" commmand.  It is not as 
easy to read visually, but it is easier for others to copy into R.)

	  Please follow Doug Bates' advice:

	  1.  Plot the data.

	  2.  Play with the nonlinear formula to understand what the particular 
coefficients do.

	  3.  Use algorithm = "plinear".

	  ** If you did the above, you would find out that you "data" are 
entirely linear.  What values for the parameters to you need to make 
your nonlinear formula (approximately) linear?  I don't have time to 
analyze it right now, but you may need to send b to 0 and c. to Inf. 
Compute a second-order Taylor approximation to your formula to find out.

	  Also, please set "trace=TRUE":  Then the algorithm will tell you what 
it is trying to do with the parameter estimates.

	  You are persistent, Andrea:  You will get an answer.

Best Wishes,
Spencer Graves

Andrea Calandra wrote:
> 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
> 
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