[R] nls and na/Nan/Inf error

[Gabor Grothendieck]

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 <tony.meissner at bigpond.com> 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
>
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