[R] nls: Fitting two models at once?

Martin Ballaschk qcumba at web.de
Fri Nov 7 22:33:40 CET 2008

```Dear Heather!

Thank you very, very much for your solution which also reproduces exactly
the results I get from the SigmaPlot analysises. :)

Martin

Heather Turner schrieb:
> Dear Martin,
>
> You can use the same idea of concatenating the data in R. The following
>
> spec <- c(asfe, dias)
> n1 <- length(asfe)
> n2 <- length(dias)
> CYT <- c(28 * CYTF, 24.6 * 2 * CYTB6)
> B559HP <- c(B559HP, numeric(n2))
> B559LP <- c(numeric(n1), B559LP)
> C550 <- c(numeric(n1), C550)
>
> spec.fit <-
> nls(
> 	spec ~ cyt.v*CYT + hp.v*B559HP + lp.v*B559LP + c550.v*C550,
> 	start = list(cyt.v = 0.00005, hp.v = 0.000003, lp.v = 1,
> 	             c550.v = 1) # arbitrary
> );
>
> or more efficiently, using lm
>
> spec.fit <- lm(spec ~ 0 + CYT + B559HP + B559LP + C550)
>
> # draw stuff
> plot(
> 	1, 2,
> 	type="n",
> 	xlim = c(540, 575),
> 	ylim=c(-0.002, 0.008),
> );
>
> # first spectrum and fit
> lines(wl, asfe, type="b", pch=19); # solid circles
> lines(wl, fitted(spec.fit)[1:n1], col = "red");
>
> # second spectrum and fit
> lines(wl, dias, type="b");
> lines(wl, fitted(spec.fit)[(n1 + 1):(n1 + n2)], col = "blue");
>
> Best wishes,
>
> Heather
>
> Dr H Turner
> Senior Research Fellow
> Dept. of Statistics
> The University of Warwick
> Coventry
> CV4 7AL
>
> Tel: 024 76575870
> Fax: 024 76524532
> Url: www.warwick.ac.uk/go/heatherturner
>
>
> Martin Ballaschk wrote:
>> Hello,
>>
>> I'm still a newbie user and struggling to automate some analyses from
>> SigmaPlot using R. R is a great help for me so far!
>>
>> But the following problem makes me go nuts.
>>
>> I have two spectra, both have to be fitted to reference data. Problem: the
>> both spectra are connected in some way: the stoichiometry of coefficients
>> "cytf.v"/"cytb.v" is 1/2.
>> {{In the SigmaPlot workflow one has to copy the two spectra into one column
>> beneath each other and the  two spectra are somehow treated as one curve -
>> like in http://home.arcor.de/ballaschk/cytbf-help/sigmaplot%20formula.png}}
>>
>> Can anybody help? :(
>>
>> I tried to condense everything to the "minimum" R script below to give an
>> impression of what I'm talking about.
>>
>> 	Martin
>>
>>
>>
>> ########################################################################
>> # "Minimal" R script reading remote data for convenience
>>
>> # first spectrum
>> # second spectrum
>>
>> # reference data for fit, wavelength = wl
>> attach(ref);
>>
>> ### FITTING, problem: 2*cytf.v == cytb.v
>>
>> # fit first spectrum to two reference spectra
>> asfe.fit <-
>> nls(
>> 	asfe ~ (cytf.v * 28) * CYTF + hp.v * B559HP,
>> 	start = list(cytf.v = 0.00005, hp.v = 0.000003) # arbitrary
>> );
>>
>> # fit second spectrum to three reference spectra
>> dias.fit <-
>> nls(
>> 	dias ~ (cytb.v * 24.6 * 2) * CYTB6 + lp.v * B559LP + c550.v * C550,
>> 	start = list(cytb.v = 1, lp.v = 1, c550.v = 1) # arbitrary
>> );
>>
>>
>> # draw stuff
>> plot(
>> 	1, 2,
>> 	type="n",
>> 	xlim = c(540, 575),
>> 	ylim=c(-0.002, 0.008),
>> );
>>
>> # first spectrum and fit
>> lines(wl, asfe, type="b", pch=19); # solid circles
>> lines(wl, fitted(asfe.fit), col = "red");
>>
>> # second spectrum and fit
>> lines(wl, dias, type="b");
>> lines(wl, fitted(dias.fit), col = "blue");
>>
>> ______________________________________________
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