Hi. I am trying to do a nonlinear regression on a set of data with Monod
kinetics and Haldane inhibition. I am using the following commands to do
the nonlinear regression:
dce<-read.delim("data.txt", header = TRUE, sep = "\t", quote="\"", dec=".",
fill = TRUE, comment.char="")
dce.m1<-nls(rate~kmax*conc/(Ks+conc+((conc^2)/Ki),data=dce
,start=list(Ks=1000,kmax=6000,Ki=10000),trace=TRUE)
I get reasonable answers for Ks, kmax and Ki from this.
However, I want to find the 95% confidence intervals for each of these
values. So I first use the command profile:
(pr <- profile(dce.m1))
And then I ususally use the following command to get the confidence
intervals:
confint(pr, level=0.95)
However, when I run the profile command, I am getting the following error:
Error in prof$getProfile() : singular gradient
Do you have any idea what this means, or what I can do to fix it?
I have attached the corresponding file with the data I'm using in case that
helps.
Thanks!
Gretchen Heavner
conc rate
1.642954108 4.460677577
1.96419336 5.369018741
2.411233484 303.4816161
2.083860628 406.5940798
3.237105618 332.5106627
1.541574251 310.1025388
0 2.746097252
0 3.236122145
0 5.387406642
2.613273505 544.3881261
1.674376521 535.2056647
1.272419565 688.773693
6506.124712 3193.54196
636.4890845 534.5243761
179.4848649 642.7148796
394.8780499 536.3999568
821.4336211 3018.968118
1985.399238 2880.47305
203.254026 1030.660214
11.6416869 446.6209406
1159.841416 2240.487362
179.1906363 1245.802977
25.32770902 562.8883166
278.1572449 709.1081229
24.3055219 249.1544286
187.6656906 678.752123
8.881946288 350.5795416
7554.586825 2724.21323
7430.314722 2745.073389
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