[R] nls() singular graident matrix error

[Dieter Menne]

Richard,


Trying to duplicate the model in R using nls(), I took the following  steps:
        Foo <- deriv( ~ tph1 * ((1 - exp(-(a1*N^a2)*age2))/ (1 -
exp(-(a1*N^a2)*age)))^(-(b1*N + b2*T +
            b3*F*T)), c("a1","a2","b1","b2","b3"), function(tph1, age2, age,
T, N, a1, a2, b1, b2, b3) {})


I had a similar problem, and tracked it down to a known bug in deriv, which
does not correctly handle unary minus signs. To check is this is the
problem,
rewrite
  exp(-(a1*N^a2)*age2))
as

  exp((-1)*(a1*N^a2)*age2))

(for all similar cases)

Even if this does not help (there might be other errors around), check
the resulting derivatives if they are correct. I never use derive unchecked,
but only to generate an expression and paste that expression into my
program.

Dieter

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