doc_Bb_bcs.h

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/** \page LBSBCs Boundary Conditions
 
LBS supports the boundary condition `"incident_anisotropic_heterogeneous"`,
which allows for a very intricate type of boundary condition to be specified.
 
For example, consider the boundary condition applied to boundary `zmax` below:
\code
chiLBSSetOptions(phys1,
{
  spatial_discretization = "pwld",
  scattering_order = 2,
  boundary_conditions =
  {
    { name = "zmax", type = "incident_anisotropic_heterogeneous",
      function_name = "luaBoundaryFunctionA"},
  }
})
\endcode
 
It points to the lua function `"luaBoundaryFunctionA"`. This lua function will
be called with the following parameters:
```
size_t        cell_global_id,
int           cell_material_id,
unsigned int  face_index,
unsigned int  face_node_index,
const chi_mesh::Vector3& face_node_location,
const chi_mesh::Vector3& face_node_normal,
const std::vector<int>& quadrature_angle_indices,
const std::vector<chi_mesh::Vector3>& quadrature_angle_vectors,
const std::vector<std::pair<double,double>>& quadrature_phi_theta_angles,
const std::vector<int>& group_indices,
double evaluation_time;
```
and must return a 1D array of data-values ordered first by angle index, then
by group index, e.g., n0g0, n0g1, n0g2, n1g0, n1g1, n1g2, etc.
 
Example lua function:
\code
function luaBoundaryFunctionA(cell_global_id,
                              material_id,
                              location,
                              normal,
                              quadrature_angle_indices,
                              quadrature_angle_vectors,
                              quadrature_phi_theta_angles,
                              group_indices)
    num_angles = rawlen(quadrature_angle_vectors)
    num_groups = rawlen(group_indices)
    psi = {}
    dof_count = 0
 
    for ni=1,num_angles do
        omega = quadrature_angle_vectors[ni]
        phi_theta = quadrature_phi_theta_angles[ni]
        for gi=1,num_groups do
            g = group_indices[gi]
 
            value = 1.0
 
            dof_count = dof_count + 1
            psi[dof_count] = value
        end
    end
 
    return psi
end
\endcode
 
An example of a very intricate use of this functionality can be seen in the
test \ref tests_Transport_Steady_Transport2D_5PolyA_AniHeteroBndry_lua
 
\ingroup LBSUtilities */