----
n1 <- nlxb(y~theta1 - theta2*exp(-theta3*(x-8)),
start = list(theta1 = 0.4, theta2 = -0.1, theta3 = 1/5),
data = dd2)
cc <- coef(n1)
start2 <- with(as.list(cc),
list(theta1 = theta1,
theta2 = theta2*exp(theta3*8),
theta3 = theta3))
unlist(start2)
n2 <- nlxb(y~theta1 - theta2*exp(-theta3*x),
start = start2,
data = dd2)
all.equal(unlist(start2), c(coef(n2)), tolerance = 1e-7)
cc2 <- coef(n2)
nlregmod2 <- nls(y ~ theta1 - theta2*exp(-theta3*x),
start =
list(theta1 = cc2[["theta1"]],
theta2 = cc2[["theta2"]],
theta3 = cc2[["theta3"]]), data=dd2)
On 2023-08-20 2:50 p.m., Paul Bernal wrote:
Dear Bert, Thank you so much for your kind and valuable feedback. I tried finding the starting values using the approach you mentioned, then did the following to fit the nonlinear regression model: nlregmod2 <- nls(y ~ theta1 - theta2*exp(-theta3*x), start = list(theta1 = 0.37, theta2 = exp(-1.8), theta3 = -0.05538), data=mod14data2_random) However, I got this error: Error in nls(y ~ theta1 - theta2 * exp(-theta3 * x), start = list(theta1 = 0.37, : step factor 0.000488281 reduced below 'minFactor' of 0.000976562 nlregmod2 <- nlxb(y ~ theta1 - theta2*exp(-theta3*x), start = list(theta1 = 0.37, theta2 = exp(-1.8), theta3 = -0.05538), data=mod14data2_random) summary(nlregmod2) Object has try-error or missing parameters nlregmod2 And I get some NA values when retrieving the statistics for the fitted model: residual sumsquares = 0.0022973 on 15 observations after 2235 Jacobian and 2861 function evaluations name coeff SE tstat pval gradient JSingval theta1 9330.89 NA NA NA 5.275e-11 967470 theta2 9330.41 NA NA NA -5.318e-11 1.772 theta3 -3.0032e-07 NA NA NA 1.389e-05 8.028e-12 Kind regards, Paul El dom, 20 ago 2023 a las 13:21, Bert Gunter (<bgunter.4...@gmail.com>) escribió:I got starting values as follows: Noting that the minimum data value is .38, I fit the linear model log(y - .37) ~ x to get intercept = -1.8 and slope = -.055. So I used .37, exp(-1.8) and -.055 as the starting values for theta0, theta1, and theta2 in the nonlinear model. This converged without problems. Cheers, Bert On Sun, Aug 20, 2023 at 10:15 AM Paul Bernal <paulberna...@gmail.com> wrote:Dear friends, This is the dataset I am currently working with:dput(mod14data2_random)structure(list(index = c(14L, 27L, 37L, 33L, 34L, 16L, 7L, 1L, 39L, 36L, 40L, 19L, 28L, 38L, 32L), y = c(0.44, 0.4, 0.4, 0.4, 0.4, 0.43, 0.46, 0.49, 0.41, 0.41, 0.38, 0.42, 0.41, 0.4, 0.4 ), x = c(16, 24, 32, 30, 30, 16, 12, 8, 36, 32, 36, 20, 26, 34, 28)), row.names = c(NA, -15L), class = "data.frame") I did the following to try to fit a nonlinear regression model: #First, Procedure to Find Starting (initial) Values For Theta1, Theta2, and Theta3 mymod2 <- y ~ theta1 - theta2*exp(-theta3*x) strt2 <- c(theta1 = 1, theta2 = 2, theta3 = 3) trysol2<-nlxb(formula=mymod2, data=mod14data2_random, start=strt2, trace=TRUE) trysol2 trysol2$coefficients[[3]] #Fitting nonlinear Regression Model Using Starting Values From Previous Part nonlinearmod2 <- nls(mymod2, start = list(theta1 = trysol2$coefficients[[1]], theta2 = trysol2$coefficients[[2]], theta3 = trysol2$coefficients[[3]]), data = mod14data2_random) And I got this error: Error in nlsModel(formula, mf, start, wts, scaleOffset = scOff, nDcentral = nDcntr) : singular gradient matrix at initial parameter estimates Any idea on how to proceed in this situation? What could I do? Kind regards, Paul [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.[[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
