.. _elements-derived:

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Explicitly Computing Derived Quantities
***************************************

.. code-block:: sierrainput

   BEGIN DERIVED OUTPUT
     COMPUTE AND STORE VARIABLE =
       <string>derived_quantity_name
   END DERIVED OUTPUT

The above command block is used to explicitly compute and store a derived quantity into an internal field. This is useful if the field is needed by an outside capability such as a transfer or error estimation.

For example, to use a derived quantity in a transfer, a ``DERIVED OUTPUT`` command block must be used. For instance, to transfer the von Mises stress norm:

.. code-block:: sierrainput

   BEGIN DERIVED OUTPUT
     COMPUTE AND STORE VARIABLE = von_mises
   END DERIVED OUTPUT

Tables :numref:`tab-output-variables-elements` through :numref:`output-tab-elevarsh` in :numref:`output` list element variables available for different types of elements. Variables that are only computed at user request are designated with a ``yes`` in the ``Derived`` column of these tables. These are the quantities that must be listed in a ``BEGIN DERIVED OUTPUT`` command block if they are to be transferred during a coupled analysis.
