Use a grid search to get the starting values in which case you will likely be close enough that you won't run into problems even without derivatives:
attach(fldgd) grid <- expand.grid(Vr = seq(0,.3,.1), Vm = seq(.45, 1, .05), alpha = seq(1,2,.25), lamda = seq(1,2,.25)) ss <- function(p) sum((Moisture - vanGen(Suction, p[1], p[2], p[3], p[4]))^2) idx <- which.min(apply(grid, 1, ss)) startval <- grid[idx,] nls(Moisture ~ vanGen(Suction, Vr, Vm, alpha, lamda), start = startval) On 9/26/05, Tony Meissner <[EMAIL PROTECTED]> wrote: > I am trying to it a particular nonlinear model common in Soil Science to > moisture release data from soil. I have written the function as shown > below according to the logist example in Ch8 of Pinheiro & Bates. I am > getting the following error (R version 2.1.1) > > *Error in qr(attr(rhs, "gradient")) : NA/NaN/Inf in foreign function > call (arg 1)* > > Below is the function and data. > > /# the van genuchten moisture release function > vanGen <- function(x, Vr, Vm, alpha, lamda) { > if (Vr < 0) Vr <- 0 > Vr + (Vm - Vr)/((1+(alpha*x)^lamda)^(1-1/lamda)) > } > vanGen <- deriv(~Vr + (Vm - Vr)/((1+(alpha*x)^lamda)^(1-1/lamda)), > c("Vr", "Vm", "alpha", "lamda"), function(x, Vr, Vm, alpha, lamda) {} )/ > > > the call in R > > /> fm1fld.nls <- nls(Moisture ~ vanGen(Suction, Vr,Vm,alpha,lamda), > + data=fldgd, start=c(Vr=0.229, Vm=0.433, alpha=0.2, lamda=1.5)) > > /and the data:/ > > /* Suction Moisture > 1 0 0.433 > 2 1 0.421 > 3 4 0.400 > 4 10 0.379 > 5 20 0.366 > 6 30 0.362 > 7 40 0.358 > 8 50 0.353 > 9 60 0.351 > 10 70 0.349 > */ > /can anyone offer any suggestions. The parameters Vr, Vm >= 0, alpha > > 0, and > lamda > 1 > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html