Full_Name: Carsten Urbach Version: 2.1.1 (2005-06-20) OS: Linux Submission from: (NULL) (141.34.5.241)
I observed one case where nls failed to return the correlation matrix, while the parameter estimates were computed correctly. In the follwing I include all the commands leading to this problem. R was started with 'R --vanilla': > version _ platform i686-pc-linux-gnu arch i686 os linux-gnu system i686, linux-gnu status major 2 minor 1.1 year 2005 month 06 day 20 language R > data <- read.table(file="zp.dat", header=F) > data V1 V2 V3 V4 1 4 5.6791 0.80709 0.00094 2 6 5.8636 0.71202 0.00083 3 8 6.0219 0.67844 0.00139 4 10 6.1628 0.65797 0.00130 5 12 6.2885 0.64604 0.00119 6 16 6.4956 0.63047 0.00112 > df <- data.frame(x=data$V2-6, y=data$V3) > df x y 1 -0.3209 0.80709 2 -0.1364 0.71202 3 0.0219 0.67844 4 0.1628 0.65797 5 0.2885 0.64604 6 0.4956 0.63047 > fit4 <- nls(y ~ a+b*x+c*x^2+d*x^3+e*x^4, data = df, start = list(a = 1., b = -1., c = 1., d=-1., e=1.)) > summary(fit4) Formula: y ~ a + b * x + c * x^2 + d * x^3 + e * x^4 Parameters: Estimate Std. Error t value Pr(>|t|) a 0.680936 0.001327 513.002 0.00124 ** b -0.168167 0.010660 -15.775 0.04030 * c 0.325593 0.047433 6.864 0.09210 . d -0.860767 0.117710 -7.313 0.08652 . e 0.957177 0.319101 3.000 0.20486 --- Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1 Residual standard error: 0.001722 on 1 degrees of freedom Correlation of Parameter Estimates: a b c d b 1 c , , 1 d * , 1 e . , * * attr(,"legend") [1] 0 0.3 . 0.6 , 0.8 + 0.9 * 0.95 B 1 > fit4 Nonlinear regression model model: y ~ a + b * x + c * x^2 + d * x^3 + e * x^4 data: df a b c d e 0.6809363 -0.1681674 0.3255929 -0.8607670 0.9571768 residual sum-of-squares: 2.966569e-06 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel