Blurb::
Hessians are needed and will be approximated by secant updates (BFGS
or SR1) from a series of gradient evaluations
Description::
The ``quasi_hessians`` specification means that Hessian information is
needed and will be approximated using secant updates (sometimes called
"quasi-Newton updates", though any algorithm that approximates
Newton's method is a quasi-Newton method).

Compared to finite difference numerical Hessians, secant
approximations do not expend additional function evaluations in
estimating all of the second-order information for every point of
interest. Rather, they accumulate approximate curvature information
over time using the existing gradient evaluations.

The supported secant approximations include the
Broyden-Fletcher-Goldfarb-Shanno (BFGS) update (specified with the
keyword ``bfgs``) and the Symmetric Rank 1 (SR1) update (specified with
the keyword ``sr1``).
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