Updates

[jeffriley]

I have made significant changes to BaseBinaryStar::Evolve(). In its current form, even when the option --emit-gravitational-radiation is not selected, COMPAS v03.01.00 creates a different detailed output file file from COMPAS v03.00.05 for the command:

./compas -n 1 --random-seed 0 --logfile-type csv --detailed-output

The value of dt is calculated differently in v03.01.00 even when --emit-gravitational-radiation is not selected. My changes reinstate the code so that v03.01.00 and v03.00.05 calculate dt in the same way (and produce identical detailed output files) when --emit-gravitational-radiation is not selected.

I believe my changes preserve the dt calculation for GW emission, but you should check this. I have checked for the command shown above, and the detailed output files when --emit-gravitational-radiation is selected are identical - EXCEPT that I have changed the code to reduce the duration of the first timestep (see comments in code). If you remove the reduction of the first timestep, the detailed output files are identical my updates vs your original code (if you choose to remove the reduction of the duration of the first timestep, you should only remove it for the GW case - it should be retained for the non-GW case).

As part of those changes I also changed BaseBinaryStar::ChooseTimestep().

I do not like this line in the code:

m_SemiMajorAxis = utils::Compare(aNew, 0.0) > 0 ? aNew : 1E-20;  // if <0, set to arbitrarily small number

Can we not avoid this kludge? Perhaps if we change the definition of HasStarsTouching() from

return (utils::Compare(m_SemiMajorAxis, 0.0) > 0) && (m_SemiMajorAxis <= RSOL_TO_AU * (m_Star1->Radius() + m_Star2->Radius()));

to

return (utils::Compare(m_SemiMajorAxis, 0.0) >= 0) && (m_SemiMajorAxis <= RSOL_TO_AU * (m_Star1->Radius() + m_Star2->Radius())); 

I don't think that will have adverse effects in other places that HasStarsTouching() is used - thoughts?

[jeffriley]

Actually, the code and comment here:

m_SemiMajorAxis = utils::Compare(aNew, 0.0) > 0 ? aNew : 1E-20; // if <0, set to arbitrarily small number

don't match. The comment says <0, but the code is <= 0. My suggested change to HasStarsTouching() will work for equals 0, but not less than 0. Still, my objection stands - surely there's a better way...

EDIT: In view of the need to get this done this weekend I'm ok to let this go and fix it later.

[ilyamandel]

Hi @jeffriley ,

I am happy with your change, modulo a request to update the declaration of ChooseTimestep() in BaseBinaryStar.h. (It will happily compile without an update because the signature stayed the same, with a const double argument, but it'll be confusing for future developers otherwise.)

I agree with your unhappiness about the kludge for "over-tightened" binaries -- see my comments on the original PR -- but that can be fixed later (the right fix is, IMHO, to stop using a negative semi-major axis as a proxy for an unbound binary).

[ilyamandel]

Thanks, @jeffriley !

I'm not sure if Adam is still online, so I'll merge this in (Adam can always check later, but I don't see anything objectionable here); please go ahead and approve Adam's original PR afterwards if you are OK with it [note my three caveats there on things to work on in the future, one of which matches yours].

[ilyamandel]

Ahh, never mind, can't roll it in -- claims I don't have write access... Which is strange, because I was able to edit Adam's PR directly on his branch via github?

[jeffriley]

Odd - I can't pull it in either. I was also able to edit Adam's branch...

[ilyamandel]

OK, I can just apply the same edits by hand to Adam's branch. ;-)