[R] Interpreting negative diagonal values in a hessian

[Andrew Robinson]

Hi R-community,

I've been trying to fit a model using maximum likelihood in nlm.  Upon convergence I examine the hessian and it has a few (not all) positive values on its diagonal, as does its inverse.  I am minimizing the negative log likelihood, so I would expect all the members of the diagonal to be negative (I think).

Can anyone shed light on how this might be interpreted?

Thanks much,

Andrew