nlregb error message

["Meissner, Tony (DWLBC)" <Meissner.Tony@saugov.sa.gov.au>]

G'day,

I am attempting to do some constrained non-linear regression using the routine nlregb.  I have defined the jacobian, but when I use in in the call, it returns the error message

Problem in nlregb.1(temp, nres, npar, liv, lv, residuals, jaco..: incorrect dimensions for Jacobian

I am running a script file listed below:

# Example SPlus script to determine contrained least squares regression

# using nlregb function. The underlying non-linear model is the Campbell

# model for modelling the moisture release curve:

# Theta(Psi) <- Theta_sat * (Psi/Psi_air)^(-1/b)

#

Campbell <- function(x, y, p) {

p[1] * (x/p[2])^(-1/p[3]) - y

}

#

# define the Jacobian ie the first derivatives wrt p[]

#

Campbell.jac <- function(x, y, p) {

dydp <- matrix(0, nrow=length(x), ncol=length(p))

tmp <- (x/p[2])^-(1/p[3])

dydp[,1] <- tmp

dydp[,2] <- p[1]*tmp/(p[2]*p[3])

dydp[,3] <- p[1]*tmp*log(x/p[2])/p[3]^2

}

#

# try unbounded first

#

x <- Psi

y <- Soil01

p <- c(0.5, 1.0, 3.0)

n <- length(x)

np <- length(p)

nlregb(nres=n, npar=np, start=p, res=Campbell,

jac=Campbell.jac, y=y,x=x,p=p)

 

Can anyone help?

Cheers
Tony Meissner
Manager - Technical Services
NRM Services
Tel: +61 8 8595 2257

Mob: +61 0401 124 971