[R] Complicated nls formula giving singular gradient message

[dave fournier]

I always enjoy these direct comparisons between different software packages.
I coded this up in AD Model Builder which is freely available at
http://admb-project.org   ADMB calculates exact derivatives via automatic
differentiation so it tends to be more stable for these difficult problems.

The parameter estimates are
# Number of parameters = 3
Objective function value = 307873.  Maximum gradient component = 1.45914e-06
# NS:
0.00865232633386
# LogKi:
-8.98700621813
# BMax:
237135.365156
The objective function is just least squares.
So it looks like SAS did pretty well before dying.