This function computes the Fisher information matrix log likelihood term with respect to beta.
marg_loglike_poisson_fisher(beta, reported, Q, lnPmat)
A spline parameter vector length num_params.
An integer vector of reported cases.
A spline basis matrix Tmod x num_params.
A matrix size Tobs x Tobs, log of make_likelihood_matrix.
A numeric vector, gradient of log likelihood value with respect to beta.