Andrea Calandra <[EMAIL PROTECTED]> writes: > I'm a student in chemical engineering, and i have to implement an algoritm about > FIVE PARAMETERS INTERPOLATION for a calibration curve (dose, optical density) > > 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 > > Have you never seen this formula, because i don't fine information or > lecterature about solution of this!!!
This is one parameterization of the four-parameter logistic growth curve. A slightly different version is available as the selfStart model SSfpl in the nls package. In R try library(nls) ?SSfpl example(SSfpl) to see how nls and SSfpl can be used. The example even produces a figure for you showing what the SSfpl parameters represent. A literature reference for the SSfpl form of the four-parameter logistic is Appendix C.6 in Pinheiro and Bates (2000), "Mixed-effects Models in S and S-PLUS", Springer. ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help