- Postprocessors are used to compute aggregate values from solution fields.  For example: average velocity, total heat flux, maximum temperature, etc.
 - MOOSE comes with several standard Postprocessors, but you can also inherit from the Postprocessor class and customize it for a particular problem.
 - Here, an `ElementAverageValue` is used to compute the average temperature of the column:
$$$
T_{avg} \equiv \frac{1}{|\Omega|} \int_{\Omega}T \; dx
$$$
where $$|\Omega|$$ is the "volume" of the domain.
 - Additionally, the `SideFluxIntegral` `Postprocessor` is used to compute the flux through the outlet:
$$$
q_{out} \equiv \int_{\partial \Omega} -k \nabla T \cdot \mathbf{n} \; ds
$$$

[Postprocessors](/wiki/MooseSystems/Postprocessors)

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## Postprocessor Source Code 

[framework/include/postprocessors/ElementAverageValue.h](https://github.com/idaholab/moose/blob/devel/framework/include/postprocessors/ElementAverageValue.h)

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[framework/src/postprocessors/ElementAverageValue.C](https://github.com/idaholab/moose/blob/devel/framework/src/postprocessors/ElementAverageValue.C)

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[framework/include/postprocessors/SideFluxIntegral.h](https://github.com/idaholab/moose/blob/devel/framework/include/postprocessors/SideFluxIntegral.h)

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[framework/src/postprocessors/SideFluxIntegral.C](https://github.com/idaholab/moose/blob/devel/framework/src/postprocessors/SideFluxIntegral.C)

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[step08_postprocessors/problems/step8.i](https://github.com/idaholab/moose/blob/devel/tutorials/darcy_thermo_mech/step08_postprocessors/problems/step8.i)