Status of the spectral solver

[RemiLehe]

This issue keeps track of the progress on the spectral solver, and what remains to be done:

• Port the non-hybrid solver from Fortran to C++ Implement PSATD solver in C++ #95
• Implement real-to-complex FFT Implement real-to-complex FFT #98
• Have the solver work on GPU, by linking cuFFT Add cuFFT code to spectral solver #96 - implemented in Spectral cufft on gpu #177
• Allow the spectral solver to compile for GPU without FFTW being installed (i.e. put all FFTW include/calls inbetween #ifdef)
• Implement OpenMP parallelization and tiling, for the relevant parts of the spectral solver
• Stop using the hybrid decomposition, when only local FFT are performed Execute spectral solver from the regular grid, instead of the dual grid #99
• Implement spectral solver with PML PSATD solver in PML #122
• Have the spectral solver work with mesh refinement Enable mesh refinement with PSATD #251
• Have the spectral solver work with load-balancing Regrid the spectral solver object when doing load-balancing #1139
• Implement the Galilean algorithm Galilean PSATD with shift  #704
• Implement more advanced Galilean-like algorithms Averaged Galilean PSATD #869
• Investigate and fix the small differences (typically 1.e-3 relative difference) between the psatd.hybrid_mpi_decomposition=0 (using C++ code) and psatd.hybrid_mpi_decomposition=1 (using PICSAR Fortran code) - see Fix bugs in the spectral solver #104

[mrowan137]

PR #1815 may partially address "Have the spectral solver work with load-balancing #1139".