Yes - it works.  Thanks!

On Friday, August 8, 2014 4:38:10 AM UTC-4, Robert Cimrman wrote:

On 08/07/2014 10:43 PM, Geoff Wright wrote:
> Hi Robert,
>
> Me again :) but I think this one is easy...  in the previous thread about
> flux I was computing electric field from voltage in the post processing
> step.  I would like to compute energy density also, from electric field.  I
> believe its something like this, in the post_process hook:

Yes, this is easy.

>      # compute the electric field
>      electric_field = pb.evaluate('ev_grad.i1.Omega( v )', mode='el_avg')
>      electric_field *= -1.0
>      out['electric_field'] = Struct(name='Electric field', mode='cell',
> data=electric_field, dofs=None)
>
>      # compute the energy density
>      energy_density = pb.evaluate('dw_volume_dot.i1.Omega(p.sigma, ef, ef)',
> ef=electric_field)
>      out['energy_density'] = Struct(name='Energy density', mode='cell',
> data=energy_density, dofs=None)
>
>
> However, I get an error when its parsing the variables.  How do I specify
> ef variable properly?  I attached the relevant files in case its necessary.

You cannot use values in QP or element averages (energy_density) in place of
term arguments - those has to be field variables. It is possible to get QP
values back into a variable, but I would not recommend it - there would be
interpolation involved and precision loss. Instead, compute all the derived
quantities in QP:

     from sfepy.linalg import dot_sequences
     from sfepy.discrete.common.mappings import get_jacobian

     # Electric field E in QP.
     ef = pb.evaluate('ev_grad.i1.Omega(v)', mode='qp')

     # E^T E in QP.
     ed = dot_sequences(ef, ef, 'ATB')

     # Scalar sigma in QP.
     mat = pb.get_materials()['p']
     sigma = mat.get_data(('Omega', 'i1'), 0, 'val')

     # Energy density in QP.
     ed = sigma * ed

     # Jacobian in QP.
     var = pb.get_variables()['v']
     det = get_jacobian(var.field, pb.integrals['i1'])

     # Element averages.
     energy_density = (ed * det).sum(1) / det.sum(1)
     energy_density = energy_density[..., None]
     out['energy_density'] = Struct(name='Energy density', mode='cell',
                                    data=energy_density, dofs=None)

     # Total energy.
     total_energy = (ed * det).sum()

I tried the above in the sphere_disc_inside_sphere.py and it worked. Let me
know it if is what you need.

r.