rebound should have some --help ?

[teuben]

Currently the system seems to promote a single binary "rebound" (athena does something similar). In athena we have a self-describing feature, in that case -h will describe for which kind of physics it was compiled. With a little extra requiremenrt in the problem.c one could make the executable a little more self-describing.

Alternatively, I could rename the binary to rebound_ or something like it.

as i'm writing this, I have a deja-vu on this issue.

[hannorein]

I'm not sure it's the same as for ATHENA. REBOUND is a shared library. It is only compiled once. Almost all options (collision routines, integrators, etc) are set at runtime. There are only a few options that are set at compile time (whether MPI or OpenMP are used). What the user does with the library is out of REBOUND's control. The examples provide a simple Makefile and a problem.c file with a main routine. That would be the place to implement the self-describing feature you're suggesting. But that's really up to the user.

[hannorein]

Two more thoughts:

• The git hash is included as a string constant in the shared library. That is helpful if one is lost where the binary comes from (assuming one is using git). The constant is called reb_githash_str. To print it in a program use printf("%s\n", reb_githash_str);. To print it from the command line one can use for example strings librebound.so | grep -x '.\{40\}'.
• If one wants to find out what settings have been used for a given simulation, then one can use the reb_simulation_diff function. This will print all changes that a user has made to a vanilla simulation:

  #include "rebound.h"
  #include <stdio.h>
  #include <stdlib.h>
  
  int main(int argc, char* argv[]) {
      struct reb_simulation* r = reb_simulation_create();
      r->G = 2.;
      reb_simulation_add_fmt(r, "m", 1.);
      reb_simulation_add_fmt(r, "m a e", 1e-3, 1., 0.1);
  
      struct reb_simulation* r_empty = reb_simulation_create();
      reb_simulation_diff(r, r_empty, 1);
  }

[teuben]

Understood. I took the plummer example in rebound, and nemo-fied this as an example how a 3rd party could use it. In case I wind up giving this hypothetical talk, it would be my NEMO example. Looks promising so far.