Nek5000/Nek5000#504

• add dt = targetCFL(+max=...) to par
• add targetCFL key to par

For reference:
https://github.com/Nek5000/Nek5000/blob/master/core/subs1.f#L178

• MPI
• gslib's sarray_transfer

Currently our jit-compilation relies on system(). This can be troublesome (see e.g. #166) and lead to an undefined behaviour.

Updates:
d39e9d3: This commit ensures that we don't call system() provided that the user runs nrspre first.

1. Cross compilation
   Our current --build-only will not work in a cross compiling context using a different front end (compiler, CPU-arch, GPU etc). In this case one has precompile on the compute node provided this is supported.

2. OCCA relies on system() to jit-compile kernels. Using nrspre will precompile all required kernels. The actual will then load the kernels from cache. Another option (not available yet) would be to switch a true runtime compilation (e.g. NVRTC for Cuda). However this might be not supported for all backends. Moreover it doesn't allow caching.

There is some libP legacy during the setup phase:

Non-scaleable communication:

• non-scaleable MPI_Allgather(...)
• non-scaleable MPI_AllToAll(ellipticBuildContinuousHex3D, meshParallelConnect)

Non-scaleable data:

• mesh->boundaryInfo holds (face vertex ids, boundaryID) for the whole mesh

To support 2D and 3D at the same time:
insVelocityDirichletConditions3D -> insVelocityDirichletConditions

• switch to new bcData struct for all elements types
• disable TOMBO support for tris, tets
• remove makefile changes (except if they are HYPRE related)
• don't build HYPRE by default
• merge our libP changes into libP's experimental branch
• port ins to staging (Noel)
• update nekRS to staging

We have observed a few cases where HYPRE's BoomerAMG is diverging.

• TOMBO + HEX only
• including okl

Encapsulate into a namespace and load needed function dynamically at runtime.

Current dependencies:

• mesh struct
• setupAide struct
• elliptic struct

Currently I cannot think of a way to sync them.

This can include libP's linAlg (available in staging) and our own operations.

• merge CDS PR into our libP next branch

• update to latest BC treatment
• add tolerance and diffusitivty to cds struct
• add pointer to cds struct to ins struct

• Integrate CDS solver into nekRS

• add our own insSetup() and clean it up
• add CDS to nekRS build system
• pass number of scalars to mkSIZE
• set nek's ifheat and npscal
• read nek's boundaryID into mesh->EtoB
• read in insSetup nek's cbc (for field 1 and 2) into ins->EtoB and cds->EtoB
• add scalar support to nek_copyTo() and nek_copyFrom ()
• call cdsSetup in nekrs.cpp:main
• call cdsSolveStep in timerstepper:runPlan4

• BC Treatment

• Introduce ins->EtoB and cds->EtoB
• Support Dirichlet + non-zero Neumann (cdsDirichletCondition/cdsNeumannCondition)
• Add sM and sP to bcData struct
• velocity value shall be accessible in cdsDirichletCondition and cdsNeumannCondition
• scalar value shall be accessible in insDirichletCondition and insNeumannCondition

• Support user specified source term

• add scalarSource function pointer to udf sturct
• call function pointer in timerstepper:runPlan4

• Extend par reader

• read tolerance and diffusivity and set correspondig internal libP parameter

• Add RBC example