Laura,

Hacking the function is straightforward. Change this line:

hessian <- control$hessian

into

hessian <- FALSE

and then this one:

vc <- -solve(as.matrix(fit$hessian))

as

vc <- diag(1, length(fit$par), length(fit$par))

Then you take care of the unexported model_offset_2 function as
pscl:::model_offset_2 and you are good to go.

*BUT*, is this really what you want? Maybe you want to get around
asymptotics by doing bootstrap.

Cheers,

Peter

--
Péter Sólymos, Dept Biol Sci, Univ Alberta, T6G 2E9, Canada AB
solymos@ualberta.ca, Ph 780.492.8534, http://psolymos.github.com
Alberta Biodiversity Monitoring Institute, http://www.abmi.ca
Boreal Avian Modelling Project, http://www.borealbirds.ca


On Mon, Sep 23, 2013 at 9:29 AM, Lee, Laura <laura.lee@ncdenr.gov> wrote:

> Hi all!
>
> I'm using a zero-inflated model using the function 'zeroinfl' and running
> into convergence problems (system is computationally singular). How can I
> modify the code so it does not calculate a Hessian matrix?
>
> Thanks,
>
> Laura
>
>
>
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