[R] Fitting data from a spectrophotometer.

[Gabor Grothendieck]

Perhaps you really prefer something with a continuous first derivative?
In that case, all the continuous cumulative distribution functions have 
a sigmoidal shape and might be suitable.  You could fit pnorm, plogis or tanh
with suitable scaling and location parameters using nls.  An example
of fitting a logistic is at

https://stat.ethz.ch/pipermail/r-help/2004-April/048385.html 


TAPO (Thomas Agersten Poulsen <tapo <at> novozymes.com> writes:

: 
: Dear R-list,
: 
: 	It is not uncommon for laboratory equipment (e.g. spectrophotometers) 
to have a linear response in a
: certain interval and then go into saturation. I wonder if there is an R-
function that models this; for
: instance by estimating the breakpoint and fitting a line below the 
breakpoint and a constant above.
: 
: Best regards
: Thomas Poulsen