* Boundary lazy comm v2

* fixes

* use pytato branch

* use staple_distributed_send

* add lazy option to wave-op-mpi

* ci fix

* initial actx support

* _RankBoundaryCommunicationLazy: do not convert to/from numpy, flatten

* Prototype MPIPytatoPyOpenCLArrayContext

* Drop evt.wait in distributed actx

* cross_rank_trace_pairs: set 'unique' tag per obj array component

* Drop commented-out graph vis from mpi+lazy actx

* add clone()

* only use Lazy boundary comm when running with lazy actx

* fix git branch

* remove duplicate requirement

* accept distributed+parallel actx

* wave-op-mpi: add simple timing

* fix MPISingleGridWorkBalancingPytatoArrayContex

* fix spelling

* initial lazy batched comm

* select comm class based on actx

* flake8

* use meshmode lazy actx

* test: use random tag

* undo random tag change

* use random tag again

* another tag fix

* debug tracepair

* add dbg

* more dbg

* Use structured tags for lazily-communicated array containers

* MPISingleGridWorkBalancingPytatoArrayContext: Convert symbolic to numeric comm tags

* more type annotation

* support running eager comm as well

* force SingleGridWorkBalancingPytatoArrayContext

* wave-op-mpi: Fix name of MPI+Pytato array context

* wave-op-mpi: Add missing mpi_communicator arg to DiscretizationCollection

* Distributed actx: deduplicate data wrappers before partitioning

* undo pytato branch

* add loopy req

* test with MPI

* use serial actx if parallel not available

* rework dependency chain

* fix lint

* make wave-op-mpi run without older lazy actx

* adapt to recent arraycontext changes

* use DistributedLazyArrayContext to simplify lazy detection

* document tag arg

* Simplify distributed-lazy array context usage (#218)

* add get_reasonable_array_context_class

* add get_reasonable_array_context_class

* document tag in interior_trace_pairs

* update MPI test infrastructure

* restructure tests

* Weak wave operator: add comm tag

* Generalize MPI test orchestration for lazy

* MPI test: use actx.compile

* test fixes

* fix sin()

* Drop leap from test_mpi_communication

* Add norm assert to test_mpi_communication

* restore final_t

* Introduce an eager-MPI array context with a sym->num tag map

Co-authored-by: Andreas Kloeckner <inform@tiker.net>

* Add Euler module

* Add simple vortex example

* Document Euler operator and add pulse experiment

* Test euler examples in lazy mode

* Make rk4_step importable

* Remove copypasta from example headers

* Make vortex initial condition importable

* Add Euler convergence test to test suite

* Rename: EulerContainer -> EulerField

* Clean up vortex initial condition

* Add type annotations and rename array container

* Clean up helper functions

* Add Euler module to the docs

* Update function: dt_non_geometric_factor -> dt_non_geometric_factors

* Add timestep estimation helper function

* Add clarifying remark about timestep estimation

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* Make wavespeed argument option

* Drop dt estimator; provide characteristic lengthscales

* Expand and update documentation

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* Allow HyperbolicOperator.max_characteristic_velocity to return local data

* Add warning to dt_geometric_factors about non-volume discretizations

* Add fudge factor to surface advection time step

* Time step estimation: clean up freeze/thaw semantics

* Wave models: clean up freeze/thaw

* Variable coefficient wave model: do not nodal-reduce characteristic velocity

* Add missing freeze(...) for dim=1 case

* Add missing thaw in dt utils unit test

* Fix variable coefficient wave example

* Memoize characteristic lengths rather than geometric factors

* Use actx from wave speed DOFArray in variable coefficient operator

* Pass array context to estimate_rk4_timestep

* Ensure application actx is passed through to timestep estimation

* Update Operator method interfaces for timestepping

* Always return thawed characteristic lengthscales

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* Make nodal reductions mpi-aware

* Add clarifying remark for nodal reductions

Co-authored-by: Andreas Klöckner <inform@tiker.net>

* Use timestep estimation in mpi wave test

Co-authored-by: Andreas Klöckner <inform@tiker.net>

Co-authored-by: Alex Fikl <alexfikl@gmail.com>

Co-authored-by: Andreas Klöckner <inform@tiker.net>

For 687a28bf: Drop StrongWaveOperator, fix WeakWaveOperator, retool dagrt-fusion to use that directly

Rename grudge.Discretization to DGDiscretizationWithBoundaries, refactor sub-discr/conn getter interfaces