.. _responses-mixed_gradients:

"""""""""""""""
mixed_gradients
"""""""""""""""


Gradients are needed and will be obtained from a mix of numerical and
analytic sources


.. toctree::
   :hidden:
   :maxdepth: 1

   responses-mixed_gradients-id_numerical_gradients
   responses-mixed_gradients-id_analytic_gradients
   responses-mixed_gradients-method_source
   responses-mixed_gradients-dakota
   responses-mixed_gradients-vendor
   responses-mixed_gradients-interval_type
   responses-mixed_gradients-forward
   responses-mixed_gradients-central
   responses-mixed_gradients-fd_step_size


**Specification**

- *Alias:* None

- *Arguments:* None


**Child Keywords:**

+-------------------------+--------------------+----------------------------+---------------------------------------------+
| Required/Optional       | Description of     | Dakota Keyword             | Dakota Keyword Description                  |
|                         | Group              |                            |                                             |
+=========================+====================+============================+=============================================+
| Required                                     | `id_numerical_gradients`__ | Identify which numerical gradient           |
|                                              |                            | corresponds to which response               |
+----------------------------------------------+----------------------------+---------------------------------------------+
| Required                                     | `id_analytic_gradients`__  | Identify which analytical gradient          |
|                                              |                            | corresponds to which response               |
+----------------------------------------------+----------------------------+---------------------------------------------+
| Optional                                     | `method_source`__          | Specify which finite difference routine is  |
|                                              |                            | used                                        |
+-------------------------+--------------------+----------------------------+---------------------------------------------+
| Optional (Choose One)   | Gradient Source    | `dakota`__                 | (Default) Use internal Dakota finite        |
|                         |                    |                            | differences algorithm                       |
|                         |                    +----------------------------+---------------------------------------------+
|                         |                    | `vendor`__                 | Use non-Dakota fd algorithm                 |
+-------------------------+--------------------+----------------------------+---------------------------------------------+
| Optional                                     | `interval_type`__          | Specify how to compute gradients and        |
|                                              |                            | hessians                                    |
+-------------------------+--------------------+----------------------------+---------------------------------------------+
| Optional (Choose One)   | Finite Difference  | `forward`__                | (Default) Use forward differences           |
|                         | Type               +----------------------------+---------------------------------------------+
|                         |                    | `central`__                | Use central differences                     |
+-------------------------+--------------------+----------------------------+---------------------------------------------+
| Optional                                     | `fd_step_size`__           | Step size used when computing gradients and |
|                                              |                            | Hessians                                    |
+----------------------------------------------+----------------------------+---------------------------------------------+

.. __: responses-mixed_gradients-id_numerical_gradients.html
__ responses-mixed_gradients-id_analytic_gradients.html
__ responses-mixed_gradients-method_source.html
__ responses-mixed_gradients-dakota.html
__ responses-mixed_gradients-vendor.html
__ responses-mixed_gradients-interval_type.html
__ responses-mixed_gradients-forward.html
__ responses-mixed_gradients-central.html
__ responses-mixed_gradients-fd_step_size.html



**Description**


The ``mixed_gradients`` specification means that some gradient
information is available directly from the simulation (analytic)
whereas the rest will have to be finite differenced (numerical). This
specification allows the user to make use of as much analytic gradient
information as is available and then finite difference for the
rest.

The ``method_source``, ``interval_type``,
and ``fd_gradient_step_size`` specifications
pertain to those functions listed
by the ``id_numerical_gradients`` list.



**Examples**


For example, the objective function may be a simple analytic
function of the design variables (e.g., weight) whereas the
constraints are nonlinear implicit functions of complex analyses
(e.g., maximum stress).