# AuxKernels System

## Overview

• AuxKernel objects should go under include/auxkernels and src/auxkernels.

• They are similar to regular kernels except that they override computeValue() instead of computeQpResidual().

• They don't have Jacobians.

• Note, there is no difference between a nodal auxiliary kernel and an elemental.

• The difference is only the input file.

• An AuxKernel operates on an Auxiliary Variable.

## (Some) Values Available to AuxKernels

• _u, _grad_u

• Value and gradient of variable this AuxKernel is operating on.

• _q_point

• XYZ coordinates of the current q-point.

• Only valid for element AuxKernel !

• _qp

• Used even for nodal AuxKernels! (Just for consistency)

• _current_elem

• A pointer to the current element that is being operated on.

• Only valid for element AuxKernels!

• _current_node

• A pointer to the current node that is being operated on.

• Only valid for element AuxKernels!

• And more !

## Example 10

Look at Example 10