Hello there, I am trying to fit an exponential model using nls to some data.
#data t <- c(0,15,30,60,90,120,240,360,480) var <- c(0.36,9.72,15.50,23.50,31.44,40.66,59.81,73.11,81.65) df <- data.frame(t, var) # model # var ~ a+b*(1-exp(-k*t)) # I'm looking for values of a,b and k # formula # mod <- nls(formula = var ~ a+b *(1-exp((-k)*t)), start=list(a=0, b=10, k=0), trace=T) # It fails and I get the following error - Error in nlsModel(formula, mf, start, wts) : singular gradient matrix at initial parameter estimates I was trying different methods and looking for some solutions but nothing is working... Any suggestions how I can fix this? I appreciated any help Thanks in advance. -- View this message in context: http://r.789695.n4.nabble.com/fitting-an-exp-model-tp4310752p4310752.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list 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.
