Purge .join() from mirgecom

[thomasgibson]

This PR does exactly what the title suggests. It removes all .join() calls!

Questions for the review:

• Is the scope and purpose of the PR clear?
  • The PR should have a description.
  • The PR should have a guide if needed (e.g., an ordering).
• Is every top-level method and class documented? Are things that should be documented actually so?
• Is the interface understandable? (I.e. can someone figure out what stuff does?) Is it well-defined?
• Does the implementation do what the docstring claims?
• Is everything that is implemented covered by tests?
• Do you see any immediate risks or performance disadvantages with the design? Example: what do interface normals attach to?

[majosm]

Looks good, just added a couple of questions/comments.

[majosm]

Can the @obj_array_vectorize_n_args be removed after this change? Also, the docstring should probably be updated to reflect that fields and the return value can be object arrays now.

I think with inducer/arraycontext#128 it may be possible to implement this function as something along the lines of:

    def filter_scalar(f):
        dd_nodal = dof_desc.as_dofdesc(dd)
        dd_modal = dof_desc.DD_VOLUME_MODAL
        discr = dcoll.discr_from_dd(dd_nodal)
        actx = f.array_context
        modal_map = dcoll.connection_from_dds(dd_nodal, dd_modal)
        nodal_map = dcoll.connection_from_dds(dd_modal, dd_nodal)
        f = modal_map(f)
        f = apply_spectral_filter(actx, f, discr, cutoff, mode_resp_func)
        return nodal_map(f)

    from arraycontext import rec_map_array_container
    return rec_map_array_container(filter_scalar, field, leaf_class=DOFArray)

[thomasgibson]

You're totally right that @obj_array_vectorize_n_args can be removed, thanks for pointing that out. I also updated the docs to reflect the changes: 74558fa

I think with inducer/arraycontext#128 it may be possible to implement this function as something along the lines of:

    def filter_scalar(f):
        dd_nodal = dof_desc.as_dofdesc(dd)
        dd_modal = dof_desc.DD_VOLUME_MODAL
        discr = dcoll.discr_from_dd(dd_nodal)
        actx = f.array_context
        modal_map = dcoll.connection_from_dds(dd_nodal, dd_modal)
        nodal_map = dcoll.connection_from_dds(dd_modal, dd_nodal)
        f = modal_map(f)
        f = apply_spectral_filter(actx, f, discr, cutoff, mode_resp_func)
        return nodal_map(f)

    from arraycontext import rec_map_array_container
    return rec_map_array_container(filter_scalar, field, leaf_class=DOFArray)

I think it's certainly an option. However, I'd prefer not to tackle that in this PR.

[MTCam]

🎉 This is terrific! Thanks @thomasgibson!