Conservation checks

Phantom verifies the main conservation laws at every time step. While these quantities cannot be exactly conserved, Phantom requires that the conservation error remains below a certain threshold. The limits on conservation errors enforced by the code are listed in the table below, as well as the references to justify them and where to find them in code. Since Phantom will stop if any of these thresholds are reached, you may wish to turn these checks off (e.g. when testing something). To do so, set the I_WILL_NOT_PUBLISH_CRAP environment variable to “yes”:

export I_WILL_NOT_PUBLISH_CRAP=yes

You can also change the value of the thresholds where they are defined in the code, although this is not recommended unless you know what you are doing. These checks are turned off automatically in some setups that use more advanced features in Phantom, more details on this below.

Name	Meaning	Value	Reference	Where in the Code	Extra Information
hdivBonB_ave	Stability check for the mean divergence error \(h|\nabla\cdot \mathbf{B}|/\mathbf{B}_{(ave)}\)	0.1	Tricco+2016; Price+2018	src/main/checkconserved.f90	Suggested value for simulation to remain unaffected by divergence errors. Only used in MHD setups.
hdivBonB_max	Stability check for the maximum divergence error \(h|\nabla\cdot \mathbf{B}|/\mathbf{B}_{(max)}\)	100	Tricco+2016; Price+2018	src/main/checkconserved.f90
totmom	Check conservation of momentum	0.1	Price+2018	src/main/evolve.90	Value is somewhat arbitrary. With default settings, expect energy conservation to \(\approx 10^{-3}\), momentum to \(\approx 10^{-6}\).
angmom	Check conservation of angular momentum	0.1	Price+2018	src/main/evolve.90	Same expectations as for totmom.
etot	Check conservation of total energy	0.1	Price+2018	src/main/evolve.90	Expected to be conserved to \(\approx 10^{-3}\) with default code settings.
mdust	Check conservation	0.1	Price+2018; Ballabio+2018	src/main/evolve.90	Purpose unclear. Possibly related to dust mass conservation.

Some of the conservation checks listed above are automatically turned off when using some specific features of Phantom:

• Total energy conservation is checked only when using an adiabatic EoS with NO cooling processes and ALL the heating terms (PdV work, shock heating, resistive heating when using MHD)

• Linear momentum conservation is not checked as long as boundary particles are used.

• Angular momentum is checked only if no boundaries are used, and no non-radial forces (iexternalforce>1) are used.

• Energy, momentum and angular momentum conservation are not checked if particle injection, dynamic boundaries, or APR (adaptive particle refinement) are used.