Enable adding 4 sink particles to a disc setup

[amenafaruqi]

Type of PR:

Modification to the disc setup type to allow the following configurations:

• A system with 4 sink particles (double binary), with a circumbinary disc around the first hierarchical level secondary.
• A system with 3 sink particles, with a circumbinary disc around the first hierarchical level secondary.

Description:

• Variables added to define the orbital parameters of the second binary.
• Two new variables, discpos and discvel defined to set the position and velocity of the disc. This was needed so the disc could be centred on a binary that is not located at the origin, rather than the centre-of-mass of the entire system.
• set_multiple subroutine call added to set up a second binary.
• Command line prompts updated to include new configurations.

The last 2 rows of this table summarise the added configurations:

No. of Sinks	Disc Type	Disc Centred On
1	circumstellar	origin
2	circumprimary	primary star
2	circumsecondary	secondary star
2	circumbinary	origin
3	circumtriple	origin
3	circumbinary	first hierarchical level secondary
4	circumbinary	first hierarchical level secondary

Testing:

• Ran make SETUP=test phantomtest && ./bin/phantomtest derivs (running the full test suite was taking too long for me to see it through to the end I'm afraid!). No issues raised.
• Manually initialised 1 simulation of every possible configuration in the table above and used splash to visualise the .tmp file to check for any obvious issues. No issues raised.

Did you run the bots?

• Buildbot run (with maxdim = 1000000). No issues raised.

[danieljprice]

looks good to me, thanks Amena!