RayKernel

Description

RayKernel is the base class for the objects that calculate residual vector contributions of non-linear scalar field variables along a Ray. See also ADRayKernel for the AD version of this object. The most simple form of a RayKernel is a LineSourceRayKernel, which implements a line source along a Ray.

The use of a RayKernel is the same of a standard Kernel. In a RayKernel subclass the computeQpResidual() function must be overridden. This is where you implement your PDE weak form terms. For non-AD objects the following member functions can optionally be overridden:

• computeQpJacobian()

• computeQpOffDiagJacobian()

These two methods provide extra information that can help the numerical solver(s) converge faster and better.

Inside your RayKernel class, you have access to several member variables for computing the residual and Jacobian values in the above mentioned functions:

• _i, _j: indices for the current test and trial shape functions respectively.

• _qp: current quadrature point index.

• _u, _grad_u: value and gradient of the variable this Kernel operates on; indexed by _qp (i.e. _u[_qp]).

• _test, _grad_test: value () and gradient () of the test functions at the q-points; indexed by _i and then _qp (i.e., _test[_i][_qp]).

• _phi, _grad_phi: value () and gradient () of the trial functions at the q-points; indexed by _j and then _qp (i.e., _phi[_j][_qp]).

• _q_point: XYZ coordinates of the current quadrature point.

• _current_elem: pointer to the current element being operated on.

Also available for override are:

• precalculateResidual()

• precalculateJacobian()

• precalculateOffDiagJacobian()

which are insertion points immediately before computing residuals and Jacobians. These methods can be useful when computing cached values that are valid for all quadrature points.

Many other useful member variables exist that describe the Ray segment. For more information, see Using a RayKernel.