Key System Parameters: sph.input

The file sph.input is used to enter in most of the key run parameters into the code. It is read in during all of the initialization subroutines, as well as when a run is being restarted. For your convenience, the testinput utility can create this file for you, based on your responses to its questions.

The sph.input file is stored in ASCII format, such that it can be read into the program in the form of the ``INPUT'' namelist, defined at the end spha.h. It includes the following variables:

TF:

The time at which the run will end, in code units. New runs start from $t=0$, restarted runs start from the time reached when the restart.sph file was written in the previous run.

DTOUT:

The time interval until a new permanent checkpointing file named outxxx.sph is written (see Sec. 5.2.1), where ``xxx'' is a 3-digit integer set by the code parameter NOUT.

GAM:

The adiabatic index $\Gamma$, used in the equation of state $P_i=A_i\rho_i^{\Gamma}$.

N:

Typically the number of particles to be used per star during the run, but the usage varies depending on which subroutine is called. This parameter is basically ignored if you are restarting a run. See the initialization subroutines for more on the meaning of this parameter for a given run.

NNOPT:

The optimal number of neighbors for each particle, which should generally be a factor of two less than the maximum allowed number, set by the parameter NNMAX in spha.h. We have found good results for NNOPT$=100$ for $N=10^5$ particles, letting the optimal number of neighbors increase or decrease by a factor of two for each order of magnitude change in the number of particles used. See Sec. 3.2 for more info.

NAV:

Integer parameter used to set the choice of AV routine, or lack thereof. See Sec. 3.5 for more info.

ALPHA,BETA,ETA2:

Parameters used by the AV schemes. Proper choices for each are discussed in Sec. 3.5. These can all be set to zero if AV is off.

NGR:

Sets the gravity grid boundaries to be used by the run, see Sec. 3.3.2 for the complete list.

XGRMIN,XGRMAX,YGRMIN,YGRMAX,ZGRMIN,ZGRMAX:

Usually, these are the minimum and maximum x, y, and z-values used for the gravity grid, but usage varies depending on the choice of NGR.

XGRLIM,YGRLIM,ZGRLIM:

For some choices of NGR, the extent to which the gravity grid is allowed to expand, but see Sec. 3.3.2 for the exact usage.

HMIN,HMAX:

The minimum and maximum allowed smoothing lengths for any particle. If HMIN$<0$, there is no minimum. This is actually the implementation we usually prefer.

NRELAX:

Sets the choice of the relaxation scheme being used. NRELAX$=0$ means no relaxation, 1 means single-star relaxation, and 2 is used for corotating binaries. See Sec. 3.4 for more info.

TRELAX:

The relaxation timescale used in Eqs. 3-12 and 3-13.

SEP0:

The initial binary separation for corotating and irrotational binaries, as well as for binaries on hyperbolic orbits.

QDAR:

The binary mass ratio, $q=M_2/M_1$, typically defined such that $q<1.0$.

AMNS,RNS:

Generally, the mass and radius of a single star or the primary in the binary, in code units.

RP,VPEAK:

The perihelion separation and relative velocity at infinite separation for binaries on hyperbolic orbits. See Sec. 4.5 for more info.

TRELOFF:

The time at which relaxation turns off, for runs which go into a dynamical phase after a relaxation phase. For runs where relaxation should last for the entire run, set TRELOFF > TF.

NGRAVRAD:

Integer parameter, used to determine if radiation reaction, as defined by the BDS formalism, will be included (NGRAVRAD=1) or not. See Sec. 3.6 for more info.

SOL:

For runs with radiation reaction in use, the speed of light in code units, not necessarily equal to unity.