Commit f69d0401 authored by Volker Springel's avatar Volker Springel
Browse files

added README

To build a local copy of the documentation:
- run `doxygen`
- open `doxygen/html/index.html` in a browser
See the file DEVELOPERS.
* Maximum number of particles per MPI-rank is restricted to 2^31 ~ 2 Billion
* Maximum number of groups/subhalos per MPI-rank is restricted to 2^31 ~ 2 Billion
* The total number of particles, and the total number of groups/subhalos, can however
be much larger than this if a sufficiently large number of MPI ranks is used.
* Maximum particle number in a single group or subhalo is for the default setting 2^31 ~ 2 billion,
but this can be enlarged if needed by setting the option FOF_ALLOW_HUGE_GROUPLENGTH
* The maximum number of subhalos per group is restricted nevertheless to 2^31 ~ 2 billion.
* If the legacy output formats 1/2 are used, each block in the output is restricted to 2 Gbyte in
size or less. This also means that the maximum number of particles per single output file, and the
maximum number of groups/subhalos per single group catalogue file can be at most of order 2 Billion,
normally substantially less than that. While this restriction can be circumvented by splitting output
over enough files, it provides one further motivation to use the HDF5 formay!
* Maximum number of lightcones: 256
* If more MPI-ranks than PMGRID are used, not all MPI tasks get anything to do in FFT calculations, which severely
compromises achievable work-load and memory balance. In this case, the column-based FFT algorithm is
a way out (it incurs higher cost however, as twice as many transpose operations are needed)
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