## Problem description

This is a standard nuclear engineering benchmark (IAEA number EIR-2) describing
an external-force-driven configuration without fissile materials present, using one-group
neutron diffusion approximation

(1)

The domain of interest is a 96 x 86 cm rectangle consisting of five regions:

The unknown is the neutron flux . The values of the diffusion coefficient
, absorption cross-section and the source term
are constant in the subdomains. The source in areas 1 and 3 and zero
elsewhere. Boundary conditions for the flux are zero everywhere.

This example uses multiple weak forms that are associated with different material
markers.

## Sample results

Solution:

Final mesh (h-FEM with linear elements):

Final mesh (h-FEM with quadratic elements):

Final mesh (hp-FEM):

DOF convergence graphs:

CPU time convergence graphs: