This is Nbody6++GPU, an N-body star cluster simulation code, maintained by Rainer Spurzem's team. The starting 13 commits of this repo put all old versions of Nbody6++GPU from Dec 2017 into Git system for version control.


 June 2021

 NBODY6++GPU-Dec2020 - Beijing version Dec2020 - maintained by R. Spurzem and team spurzem@nao.cas.cn
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 Note that this version has a common origin with Long Wang's github version https://github.com/nbodyx/ ,
 but it differs in quite a number of technical and a few astrophysical issues. 

 This tarball distribution is preliminary and should be replaced by a proper svn service at the same
 location in the future: http://silkroad.bao.ac.cn/repos/Nbody6++GPU-Dec2020/ 

 Recommended usage:
 
 ./configure --with-par=b1m --enable-simd=sse --enable-mcmodel=large
 make clean ; make -j 

 It is for up to one million bodies with many initial binaries. The configure script written by 
 Long Wang has a multitude of further options, check in it or ask.

 Sources are in src/Main/ . Due to urgent bugfixes few routines are later then Dec2020. 

 After make you find the executable and object files in build/  .
 
 This tarball provides two run directories: 16k_sse/ and 100k_sse/  - just test runs for 16k and 100k 
 single particles, 100 N-body time units. You have to copy the executable file to the run directories. 
 There is a little script @nb6++.run, which shows an example how to run the code on one (16k) or two 
 (100k) MPI processes. The environment variable OMP_NUM_THREADS has to be set to the desired value of 
 OpenMP threads per MPI process. (Maybe your system has it predefined). I also recommend to set
 OMP_STACKSIZE=4096M the shell where you run the code.

 Documentation: Manual in doc/nbody6++_manual.pdf  

 This code and the documentation is given without warranty, hopefully it is helpful. All may contain errors.
 The code is an offspring of Sverre Aarseth's direct N-body codes see www.sverre.com . 
 This is the code suitable for parallel and GPU accelerated runs on supercomputers and workstations. 
 It is inefficient (and even more error prone) for particle numbers below about 50k-100k particles 
 (depending on hardware). For smaller N you are advised to use Nbody6 and Nbody6GPU for single node/process.
 
 The test runs provided are just creating Plummer models and have initially only single particles. For any
 other initial model (special density profiles, initial binaries) it is recommended to provide a dat.10
 file in N-body input format (see manual). Such file can be produced by other prograns, like Mccluster.

 Seleted References:
 https://ui.adsabs.harvard.edu/abs/1999PASP..111.1333A/abstract (Aarseth: NBODY1 to NBODY6)
 https://ui.adsabs.harvard.edu/abs/1999JCoAM.109..407S/abstract (Spurzem on NBODY6++)
 https://ui.adsabs.harvard.edu/abs/2005MNRAS.363..293H/abstract (Hurley+ on SSE/BSE, earlier references therein)
 https://ui.adsabs.harvard.edu/abs/2012MNRAS.424..545N/abstract (Nitadori+: NBODY6GPU)
 https://ui.adsabs.harvard.edu/abs/2015MNRAS.450.4070W/abstract (Wang+: NBODY6++GPU)
 https://ui.adsabs.harvard.edu/abs/2021arXiv210508067K/abstract (Kamlah+: More on current stellar evol.)


  Known Problems:

  1. For systems with more than one GPU on one node the association of MPI rank id and GPU bus id is not 
     well defined, will be improved in next version.
  2. Runs with a million or more bodies and huge numbers of binaries (5% or more) use extreme amounts of
     computing time for the KS binaries (much much more than should be expected). We work on this. 
  3. On some systems heap and stack management when using OpenMP and MPI together seem to produce very
     strange errors and segmentation faults. The exact reason is not known; we work on this.

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