sph.input

Every run is controlled by a Fortran namelist in sph.input. A minimal file sets only what it needs, and anything omitted takes the default below. The file begins with &input and ends with &end:

&input
 tf=200,
 n=20000,
&end

Note

The variables, defaults and descriptions on this page are read directly from the namelist declaration and the default-initialisation block in parallel_bleeding_edge/src/init.f. There are 102 settings.

Time and output

Variable	Default	Applies to	Meaning
tf	50000	every run	desired final time to stop simulation
dtout	100	every run	how often an out*.sph files should be dumped
nitpot	1	nothing, see below	number of iterations between evaluation of the gravitational potential energy.
tjumpahead	1d30	every run	time after which a wide orbit is skipped rather than integrated, by advancing it analytically around the Kepler two-body solution. The default never fires; any other value is honoured
rjump	1d30	every run	fixed separation of the two stars beyond which a bound, receding orbit is skipped ahead by jumpahead, which advances it analytically around the Kepler two-body solution. The default never fires. Set this or rjumpfactor, not both, to turn on automatic jumping
rjumpfactor	0d0	every run	the alternative to rjump: a value above 0 makes the jump separation rjumpfactor times the larger tidal radius R*(M_other/M)^(1/3) of the two bodies, where R encloses rjumppercent percent of a body’s mass. It is remeasured at every output, so a star puffed up by earlier passages must recede farther before it jumps. The default never fires
reentryfactor	1d0	every run	after a jump the star is put back on the infalling branch of its orbit at reentryfactor times the separation it jumped from. 1 is what the published runs did: the tides the star feels on re-entry are no stronger than when it jumped. Must be above 0 and at most 1. A jump whose re-entry separation would lie inside periastron stops the run
tscanon	0	every run	time that the scan of a binary starts. The separation is held at sep0 until then, which gives the stars time to settle into the shape the corotating frame asks for
sepfinal	1.d30	every run	final separation for the scan of a binary, reached at min(tf,treloff). The scan is exponential in separation, so it changes by a fixed fraction per unit time. Set it equal to sep0 for a corotating run that does not scan
throwaway	.true.	every run	when skipping ahead, discard the debris and the material the accretor has taken, keeping only the surviving body and the point masses
internal_energy_fraction	0d0	every run	how much of a particle’s specific internal energy counts toward unbinding it when compbest3 sorts particles into components. 0 leaves it out, as Nandez, Ivanova & Lombardi (2014) argue for; 1 counts all of it, as in Kremer et al. (2022)

The particles

Variable	Default	Applies to	Meaning
n	100000	every run	desired number of particles. if n<0 then |n|=number of particles *per solar mass*. used only if making a new star.
nnopt	22+gflag	every run	controls neighbor number. leave it at 22 to get almost 40 neighbors.
equalmass	0	1es 1mc erg meq	particle mass is proportional to rho^(1-equalmass), so equalmass=1 has equal mass particles and equalmass=0 is for constant number density.
starmass	1d0	1es 1mc	mass of the polytrope to build, in solar masses
starradius	1d0	1es 1mc	radius of the polytrope to build, in solar radii
hco	-1d30	every run	softening/smoothing length for compact object or core particle (<0 for auto-set)
mco	-1d30	erg	mass of compact object or core particle
hfloor	0d0	every run	hp(i) = hptilde(i) + hfloor, where hp(i)=smoothing length and hptilde(i) is used in eq.(A1) of GLPZ 2010. With dynhco=3 instead the smooth floor hp(i)=(hptilde(i)^p+hfloor^p)^(1/p), p=hcopnorm

Equation of state and physics

Variable	Default	Applies to	Meaning
neos	1	every run	0 for polytropic equation of state (eos), 1 for ideal gas + radiation pressure, 2 for tabulated eos
gam	5.d0/3.d0	every run	leave this set at a reasonable value even if using neos=1 or 2 (because the value of gam is used in estimating the local sound speed in balav3.f)
nav	3	every run	artificial viscosity (av) flag. 3: hybrid balsara-monaghan av with alpha and beta. 4: dissipation from a riemann solver between each pair of particles, with no alpha or beta
navsw	1	every run	nav=4 only: 0 for no switch, 1 to multiply the dissipation by balsara’s switch of particle i (as nav=3 does), 2 to apply it to approaching pairs only, 3 for both
nriemann	1	every run	nav=4 only: 1 for the star pressure from toro’s adaptive guess and one halley step in p**((gamma-1)/(2 gamma)), which cannot fall to the pressure floor as a newton step in p can, with any pair whose p*-p*_0 comes out with the wrong sign solved to convergence. 0 to iterate newton to convergence
alpha	1	every run	av coefficient for term linear in mu
beta	2	every run	av coefficient for mu^2 term
ngr	3	every run	gravity flag. leave it at 3. if your want no gravity, ngr=0 might still work.
nselfgravity	1	every run	0 if just do gravity to point particles, 1 if self-gravitating
nkernel	2	every run	smoothing kernel: 0=cubic spline, 1=Wendland 3,3, 2=Wendland C4
ncooling	0	every run	0 if no cooling, otherwise radiative cooling
teq	100d0	every run	background temperature the cooling relaxes towards, in K. Only used when ncooling>0
reat	-1.d0	every run	radius within which a point mass swallows SPH particles. Negative disables eating

Relaxation

Variable	Default	Applies to	Meaning
nrelax	1	every run	relaxation flag. 0=dynamical calculation, 1=relaxation of single star, 2=relaxation of binary in corotating frame with centrifugal force, 3=calculation rotating frame with centrifugal and coriolis forces
trelax	1.d30	every run	drag timescale. 0 derives it from the model, a very large value disables the drag
treloff	0	every run	time the drag switches off and the run turns dynamical. It ends a scan as well, since a scan runs until min(tf,treloff). 0 asks for it to be derived as 10*trelax, which for a single star needs trelax=0 as well
tresplintmuoff	0.	every run	time to stop resplinting the mean molecular weight. leave this at 0.
omega_spin	0.d0	every run	angular rotation rate of star, used in nrelax=1 relaxations to give a rigidly rotating model

Orbit of the encounter

Variable	Default	Applies to	Meaning
sep0	200	every run	initial separation of two stars in a binary or collision calculation, and the separation a scan starts from and holds until tscanon
rp	-1.d30	every run	separation at closest approach. Set any two of rp, vinf2, e0 and semimajoraxis and the rest follow
impactparameter	-1.d30	hbs hyp	impact parameter at infinity, an alternative to rp, converted to it using angular momentum
e0	-1.d30	bph hbs hyp	orbital eccentricity: 1 is parabolic, above 1 hyperbolic, below 1 bound
semimajoraxis	0.d0	bph hbs hyp	orbital semimajor axis. 0 means unset, so that it is deduced from the others
vinf2	1.d30	bph hbs hyp	square of the relative speed at infinity. 1d30 means unset, so it is deduced from the others

Compact object and black hole

Variable	Default	Applies to	Meaning
mbh	10d0	2cr hbs hyp	mass of the point mass used as the second object when startfile2 is absent
dynhco	0	every run	0: point particles (u=0) keep the constant softening hco. 1: their softening is solved from eq.(A1) like an SPH smoothing length. 2: as 1 but smoothly limited to [hcomin,hcomax]. 3: every particle’s h=(htilde^p+hfloor^p)^(1/p) with htilde from eq.(A1), and point particles also capped at hcomax
hcomin	0d0	every run	dynhco=2: lower limit on a point particle’s softening length (<=0: no limit)
hcomax	0d0	every run	dynhco=2 or 3: upper limit on a point particle’s softening length (<=0: no limit)
hcopnorm	8d0	every run	dynhco=2 or 3: sharpness p of the smooth limits h=((h_dyn^p+hcomin^p)^(-1)+hcomax^(-p))^(-1/p)
bbh_m1	-1d0	hyp	first mass of a compact-object binary. Required, and only used, when bbh_m2 is positive
bbh_m2	-1d0	hyp	second mass of a compact-object binary. Negative means unset, giving a single point mass of mass mbh
bbh_rp	-1.d30	hyp	separation at closest approach for the compact-object binary
bbh_semimajoraxis	0.d0	hyp	semimajor axis of the compact-object binary. 0 means unset
bbh_vinf2	1.d30	hyp	square of the relative speed at infinity for the compact-object binary. 1d30 means unset
bbh_e0	-1.d30	hyp	eccentricity of the compact-object binary
bbh_trueanomaly	0d0	hyp	true anomaly of the compact-object binary, in degrees
bbh_argperi	0d0	hyp	argument of periapsis of the compact-object binary, in degrees
bbh_inclination	0d0	hyp	inclination of the compact-object binary, in degrees
bbh_longitude	0d0	hyp	longitude of the ascending node of the compact-object binary, in degrees

Timestep control

Variable	Default	Applies to	Meaning
nintvar	2	every run	1=integrate entropic variable a, 2=integrate internal energy u, 3=integrate buoyancy ln A (needs neos=1), 12=a then u, 32=ln A then u
cn1	.3d0	every run	dt1=cn1*h/v_signal
cn2	1.d30	every run	dt2=cn2*(h/|a-a_smoothed|)^0.5
cn3	0.1d0	every run	dt3=cn3*u/|du/dt|
cn4	1.d30	every run	dt4=cn4*v_signal/|a-a_smoothed|
cn5	0.02d0	every run	dt5=cn5*r_ij/v_ij (minimized over all other particles j)
cn6	0.02d0	every run	dt6=cn6*(r_ij/a_ij)^.5 (minimized over all other particles j)
cn7	4.d0	every run	r_ij=(x_ij^2+y_ij^2+z_ij^2+cn7*h_i^2)^.5
nblock	0	every run	0: one shared timestep. 1: block (power-of-2) timesteps, for dynamical runs only (see the docs for the settings it needs)
nbinmax	20	every run	nblock=1: smallest step is dtmaxblk/2**nbinmax
dtmaxblk	-1d0	every run	nblock=1: largest step (<=0: use dtout)
nblimit	2	every run	nblock=1: a step may be at most 2**nblimit times a neighbour’s
nblockfull	0	every run	nblock=1 testing: 1 recomputes h and hydro for all particles every substep
dtforce	-1d0	every run	testing only: >0 forces the shared timestep to this value
nstartramp	-1	every run	1: a new run from t=0 takes a first step 1/64 of what the timestep limits give, then at most doubles each step (for initial discontinuities). 0: off. <0: on only for a new shock-tube run (iname=’pbx’, nrelax=0)

Parallelism and GPUs

Variable	Default	Applies to	Meaning
ngravprocs	0	every run	the number of gravity processors (must be <= min(nprocs,ngravprocsmax))
ngravhilo	1	every run	GPU gravity only: 1 sends each position to the card as a float plus the float’s remainder, so separations keep single precision however far the pair is from the reference point (the gas centre of mass), and with block timesteps the rounding of a pair’s force cancels between its two particles. 0 sends the float alone, at the same cost for the whole system and about 15% less for the active particles of block steps, but a star far from that point loses digits in its close separations, and with nblock=1 momentum and angular momentum drift
qthreads	0	every run	number of gpu threads per particle. typically set to 1, 2, 4, or 8. set to a negative value to optimize the number of threads by timing. set to 0 to guess the best number of threads without timing.
ppn	16	every run	cpu cores per node, used to spread the gravity processes over nodes
computeexclusivemode	0	every run	set this to 1 if on machine like grapefree with gpus in compute exclusive mode; set this to 0 on supercomputers like lincoln
gflag	1	every run	set to 0 for g function from appendix of gaburov et al. (2010); set to 1 for a g function that works better when there are black holes, or 2 for G=(1-q^3)^2 with q=r/2h, which decreases strictly with r so that the h solution has no flat stretches. It gives about 3*nnopt neighbours within 2h, so it needs about half the nnopt of gflag=1 for the same neighbour count

Units

These three set the physical meaning of every code unit; see code units for what the derived units work out to.

Variable	Default	Applies to	Meaning
runit	6.957d10	every run	number of cm in the unit of length. use 6.957d10 if want MESA solar radius.
munit	1.9884098706980504d33	every run	number of g in unit of mass. use 1.9884098706980504E+033 if want MESA solar mass.
gravconst	6.67430d-08	every run	newton’s gravitational constant in cgs. 2018 CODATA value; older StarSmasher runs used 6.67390d-08

Periodic box

A positive period makes that direction periodic: positions are wrapped into the box and every pair separation uses the nearest periodic image. Each 2h must stay below half of each period. A periodic run needs ngr=0 and nblock=0, and is usually started with INAME='pbx', which reads the particles from startfile1.

Variable	Default	Applies to	Meaning
boxx	0d0	every run	period in x of a periodic box running from -boxx/2 to boxx/2. 0 leaves x open
boxy	0d0	every run	period in y, as for boxx
boxz	0d0	every run	period in z, as for boxx

Input files

Variable	Default	Applies to	Meaning
startfile1	'sph.start1u'	2cr bhe bph bps hbs hyp pbx res tri	first body of the encounter, in out*.sph format, usually the last snapshot of a relaxation
startfile2	'sph.start2u'	2cr bhe bps hyp tri	second body, same format as startfile1. If absent, a single point mass of mass mbh is used
startfile3	'sph.start3u'	tri	third body of a triple, same format as startfile1
binaryfile	'input.bs'	2cr bps	text file describing the binary, read by bps and 2cr
triplefile	'input.3s'	bhe tri	text file describing the third body, read by bhe and tri
bpbhfile	'sph.bpbh'	bph	text file giving the orientation angles and black hole mass, read by bph
imagefile	'sph.image'	txt	ASCII picture that txt turns into a particle layout
advectedfile	'sph.passivelyAdvected'	hyp	per-particle passively advected quantities, read by hyp when present
eosfile	'sph.eos'	every run	tabulated equation of state, read when neos selects a table
opacityfile	'sph.opacity'	every run	tabulated opacities, read when cooling needs them
profilefile	'eg.last1.muse_s2mm'	erg	stellar-evolution profile that erg builds its star from
stellarevolutioncodetype	1	erg	which code wrote profilefile, since the column layouts differ

Other settings

Variable	Default	Applies to	Meaning
tswitchtou	-1.d0	every run	nintvar=12 or 32: time to hand over to u. <0 means use treloff.
twozone	0	erg	1: when building a star from a profile, give equal masses to particles beyond 90% of the radius where A=P/rho^(5/3) first decreases outward (two-zone scheme). 0: n ~ rho**equalmass throughout
rtwozone	0d0	erg	twozone=1 only: >0 places the transition at this radius instead of finding it from A. <=0: 90% of the first radius beyond 10% of the star’s where A=P/rho^(5/3) decreases outward
rjumppercent	95d0	every run	the percentage of a body’s mass enclosed by the radius R in the tidal radius that rjumpfactor multiplies. Only used when rjumpfactor is set. Must be above 0 and at most 100
ndtoutafter	100	every run	once a jump-ahead run (automatic jumping on) has lost its star, leaving a point mass as the only body, run on for this many dtout and stop, unless tf comes first