r"""
Diametrically point loaded 2-D disk with postprocessing. See
:ref:`sec-primer`.

Find :math:`\ul{u}` such that:

.. math::
    \int_{\Omega} D_{ijkl}\ e_{ij}(\ul{v}) e_{kl}(\ul{u})
    = 0
    \;, \quad \forall \ul{v} \;,

where

.. math::
    D_{ijkl} = \mu (\delta_{ik} \delta_{jl}+\delta_{il} \delta_{jk}) +
    \lambda \ \delta_{ij} \delta_{kl}
    \;.
"""

from its2D_1 import *

from sfepy.mechanics.matcoefs import stiffness_from_youngpoisson

def stress_strain(out, pb, state, extend=False):
    """
    Calculate and output strain and stress for given displacements.
    """
    from sfepy.base.base import Struct

    ev = pb.evaluate
    strain = ev('ev_cauchy_strain.2.Omega(u)', mode='el_avg')
    stress = ev('ev_cauchy_stress.2.Omega(Asphalt.D, u)', mode='el_avg')

    out['cauchy_strain'] = Struct(name='output_data', mode='cell',
                                  data=strain, dofs=None)
    out['cauchy_stress'] = Struct(name='output_data', mode='cell',
                                  data=stress, dofs=None)

    return out

asphalt = materials['Asphalt'][0]
asphalt.update({'D' : stiffness_from_youngpoisson(2, young, poisson)})
options.update({'post_process_hook' : 'stress_strain',})