Blurb::
Hessians are needed and will be obtained from a mix of numerical,
analytic, and "quasi" sources

Description::
The \c mixed_hessians specification means that some Hessian
information is available directly from the simulation (analytic)
whereas the rest will have to be estimated by finite differences
(numerical) or approximated by secant updating. As for
mixed gradients, this specification allows the user to make use of as
much analytic information as is available and then
estimate/approximate the rest. 

The \c id_analytic_hessians list
specifies by number the functions which have analytic Hessians, and
the \c id_numerical_hessians and \c id_quasi_hessians lists specify by
number the functions which must use numerical Hessians and
secant Hessian updates, respectively. Each function identifier,
from 1 through the total number of functions, must appear once and
only once within the union of the \c id_analytic_hessians, \c
id_numerical_hessians, and \c id_quasi_hessians lists. 

The \c
fd_hessian_step_size and \c bfgs, \c damped \c bfgs, or \c sr1
secant update selections are as described previously in \ref
responses and pertain to those functions
listed by the \c id_numerical_hessians and \c id_quasi_hessians
lists.


Topics::	
Examples::
Theory::
Faq::
See_Also::	responses-no_hessians, responses-numerical_hessians, responses-quasi_hessians, responses-analytic_hessians
