Tree-based neighbor search

Performance enhancements:

• Octree-based warp-aware neighbor searches for better performance and quasi-2D geometry support
• Adaptive target particle groups for gravity traversal based on bounding volumes relative to volumes of local leaf cells. Avoids large traversal stacks.
• Support for multi-level tree merges for faster octree rebalancing. Avoids a rare issue where LET updates couldn't keep up
  with changing domain boundaries. (Loss of a peer rank followed by inability to scale back the octree to the global resolution in a single step)

New features:

• Support for particle splitting when initializing from a checkpoint file.
• Support for initialization of rectangular domains at scale for Kelvin-Helmholtz and Wind-shock
• Pure N-body gravity propagator
• Coupled update of neighbor counts and smoothing lengths

Minor fixes and enhancements:

• IAD tau determinants with normalization factors for better over/underflow resilience
• Correct observable selection handling and settings parameter when writing and restoring from file
• More robust initial domain synchronization that avoids the MPI_Send limit of MPI_INT32 elements per message.
• Modify signalling velocity for larger time-steps
• Added divergence of velocity based minDtRho criterium to time-step control
• Added acceleration-based time-step control

AV cleaning

• Added artificial viscosity cleaning as a feature
• Added interface to GRACKLE for radiative cooling
• Improvements to Domain: perform octree updates and halo discovery on GPUs
• Bugfix: added missing device synchronization points in domain and halo exchange when using GPU_DIRECT=ON

v0.6

• Volume elements are now the default type of SPH, implemented on the GPU
• Support for large-scale gravity through Ryoanji
• HIP-support
• GPU-direct halo exchange
• Expanded test case selection
• Turbulence stirring

Unified application front-end

Introduces a single SPH application with support for

• named test cases without input files
• initialization from HDF5 files
• parallel HDF5 output with runtime selectable particle fields
• glass-like initial conditions (isotropic mean inter-particle distances)
• insitu visualization interfaces

Hilbert curve

• Adds support for using a Hilbert instead of Z-curve. Enabled by default, but switchable to Z-curve
• Fixed a GPU memory leak
• Partial support for HIP

Focused Octree

This release adds a new domain class that builds a locally focused octree based on
a slim coarse global octree and point-to-point communication.

Scaling test outputs:

SPH-EXA/v0.2.2

Merge pull request #82 from unibas-dmi-hpc/fix-cmake-cuda

fix CMake CUDA language detection

v0.2

Working Sedov and Evrard with MPI, OMP and CUDA.
The kernels uses a tree to perform all operations (neighbors, gravity, etc)