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sumfun
2008 May 23
3
nls diagnostics?
...la, mf, start, wts) :
singular gradient matrix at initial parameter estimates
This example is obviously stupid, but other singular gradient
problems are not so obvious.
If we transfer this problem to 'optim', we can get diagnostics
from an eigen analysis of the hessian:
dumfun <- function(x, y, one){
d <- y-(x[1]+2*x[2])*one
sum(d^2)
}
optimToyProblem <- optim(c(a=1, b=1), dumfun, hessian=TRUE,
y=DF1$y, one=DF1$one)
eigen(optimToyProblem$hessian, symmetric=TRUE)
$values
[1] 9.000000e+01 -7.105427e-10
$vectors
[,1] [...