[firedrake] RT/BDM works but not TH/VMS

[Justin Chang]

Hi all,

So given this Darcy problem:

  a = (dot(v, w) - p*div(w) - div(v)*q)*dx
  L = f*q*dx

where f = "12*pi*pi*sin(pi*x[0]*2)*sin(pi*x[1]*2)*sin(2*pi*x[2])" and with
these solver options:

'ksp_type': 'gmres',
    #'ksp_monitor_true_residual': True,
    'pc_type': 'fieldsplit',
    'pc_fieldsplit_type': 'schur',
    'pc_fieldsplit_schur_fact_type': 'upper',
    'pc_fieldsplit_schur_precondition': 'selfp',
    'fieldsplit_0_ksp_type': 'preonly',
    'fieldsplit_0_pc_type': 'bjacobi',
    'fieldsplit_0_sub_pc_type': 'ilu',
    'fieldsplit_1_ksp_type': 'preonly',
    'fieldsplit_1_pc_type': 'hypre',
    'fieldsplit_1_pc_hypre_type': 'boomerang'

And without specifying any boundaries (my forcing function f is chosen so
that the pressure is homogeneous on the boundary), RT0 and BDM works
beautifully.

However, with Taylor-Hood elements and VMS (which is equal order CG1 plus a
least squares stabilization), the velocity works but the pressure solution
is screwed up.

Why is that?

Thanks,
Justin
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