Comment (by Gabriele Bozzola):

        CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
                    "VolumeIntegrals_GRMHD:file_output_routines.C Problem creating directory '%s' "
                    "for output", actual_dir);

The thorn name here is VolumeIntegrals_GRMHD which is not the correct one.

The thorn’s output is non-standard because it deals with arrays, not grid functions. Each particles' position is evolved using the thorn’s own RK method. Thus each line of the output file looks like “time x_1 y_1 z_1 x_2 y_2 z_2 …” where the subscript is the particle ID and (x,y,z) the particle position.

The positions are already grid arrays, why not outputting those with Carpet directly? E.g., one could directly output particle_tracerET::particle_position_xas an HDF5 file in CarpetIOHDF5 (or as an ASCII file in CarpetIOASCII). (In that case, it would be nice if the size of the array was not hardcoded in the interface.ccl).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2691/new-features-to-particle_traceret