

# Code Configuration









Basic operation mode



============================






The default running mode (without any of the flags active) is 3d with 6 particle types;



type 0 is always gas; types >0 are only gravitationally interacting.









**NTYPES=6**






The number of particle types used. Minimum: 2.













**TWODIMS**






Simulation in 2d. Z coordinates and velocities are set to zero after reading



in initial conditions.













**ONEDIMS**






Simulation in 1d. Y and Z coordinates and velocities are set to zero after



reading in initial conditions.













**ONEDIMS_SPHERICAL**






Spherically symmetric 1d simulation. Use together with ``ONEDIMS``.



The first dimension is used as the radial coordinate.













Computational box



================================






The default running mode (without any of the flags active) is a cubic box with



periodic boundary conditions






**LONG_X=10.0**






These options can be used to distort the simulation cube along the



given direction with the given factor into a parallelepiped of arbitrary aspect



ratio. The box size in the given direction increases from the value in the



parameterfile by the factor given (e.g. if Boxsize is set to 100 and ``LONG_X=4``



is set the simulation domain extends from 0 to 400 along X and from 0 to 100



along Y and Z.)













**LONG_Y=2.0**






Stretches the y extent of the computational box by a given factor.













**LONG_Z=10.0**






Stretches the z extent of the computational box by a given factor.













**REFLECTIVE_X=1**






Boundary conditions in x direction. 1: Reflective, 2: Inflow/Outflow; not set: periodic













**REFLECTIVE_Y=1**






Boundary conditions in y direction. 1: Reflective, 2: Inflow/Outflow; not set: periodic













**REFLECTIVE_Z=1**






Boundary conditions in z direction. 1: Reflective, 2: Inflow/Outflow; not set: periodic













Hydrodynamics



=============






The default mode is: ``GAMMA=5/3`` ideal hydrodynamics






**NOHYDRO**






No hydrodynamics calculation. Note that simply not including any type 0



particles has the same effect.













**GAMMA=1.4**






Adiabatic index of gas. 5/3 if not set.













**ISOTHERM_EQS**






Isothermal gas. Code uses an isothermal Riemannsolver.













**PASSIVE_SCALARS=3**






Number of passive scalar fields advected with fluid (default: 0).













**NO_SCALAR_GRADIENTS**






Disables time and spatial extrapolation for passive scalar fields. Use only if



you know why you are doing this.













Magnetohydrodynamics



====================






By default, code only computes hydrodynamics. Note that for comparison of



MHD and hydrodynamics runs, it is sometimes useful to keep the MHD settings



active and to initialize the magnetic field to zero everywhere. The equations



of ideal MHD ensure that the magnetic field stays exactly zero throughout



the calculation.






**MHD**






Master switch for magnetohydrodynamics.













**MHD_POWELL**






Powell div(B) cleaning scheme for magnetohydrodynamics.













**MHD_POWELL_LIMIT_TIMESTEP**






Additional timestep constraint due to Powell cleaning scheme.













**MHD_SEEDFIELD**






Uniform magnetic seed field of specified orientation and strength set up after reading in IC.













Riemann solver



==============






By default, an iterative, exact (hydrodynamics) Riemann solver is used. If one of the



flags below is active, this is changed. Only one Riemann solver can be active.






**RIEMANN_HLLC**






HLLC approximate Riemann solver.













**RIEMANN_HLLD**






HLLD approximate Riemann solver (required for MHD).













Mesh motion



==============================






The default mode is a moving mesh.






**VORONOI_STATIC_MESH**






Assumes the mesh to be static, i.e. to not change with time. The vertex



velocities of all meshgenerating points is set to zero and domain



decomposition is disabled.













**VORONOI_STATIC_MESH_DO_DOMAIN_DECOMPOSITION**






Enables domain decomposition together with ``VORONOI_STATIC_MESH`` (which is



otherwise then disabled), in case nongas particle types exist and the use of



domain decompotions is desired. Note that on one hand it may be advantageous



in case the nongas particles mix well or cluster strongly, but on the other



hand the mesh construction that follows the domain decomposition is slow for a



static mesh, so whether or not using this new flag is overall advantageous



depends on the problem.













**REGULARIZE_MESH_CM_DRIFT**






Mesh regularization. Move mesh generating point towards center of mass to make



cells rounder.













**REGULARIZE_MESH_CM_DRIFT_USE_SOUNDSPEED**






Limits Mesh regularization speed by local sound speed.













**REGULARIZE_MESH_FACE_ANGLE**






Uses maximum face angle as roundness criterion in mesh regularization.













Refinement



===========================






By default, there is no refinement and derefinement and unless set otherwise,



the cirterion for refinement/derefenment is a target mass.






**REFINEMENT_SPLIT_CELLS**






Allows refinement.













**REFINEMENT_MERGE_CELLS**






Allows derefinement.













**REFINEMENT_VOLUME_LIMIT**






Limits the volume of cells and the maximum volume difference between



neighboring cels.













**JEANS_REFINEMENT**






Refinement criterion to ensure resolving the Jeans length of cells.













**REFINEMENT_HIGH_RES_GAS**






Limits the dynamical (de)refinements of cells to cells which are either



already present in the ICs or are created with ``GENERATE_GAS_IN_ICS`` from



type 1 particles. This adds an additional integer quantity ``AllowRefinement``



to PartType0 in the snapshots indicating if a gas cell is allowed to be



refined and if it is, how often this cell has already been split: if 0, no



splitting allowed. If odd (starting at 1), the cell was already present in the



ICs. If even (starting at 2), the cell was generated from a type 1 particle.



For values of 3 or more, ``floor((AllowRefinement1)/2.0)`` gives the number



of times the cell was split.













**NODEREFINE_BACKGROUND_GRID**






The background grid will be prevented from derefining, when refinement is



used. In practice, when enabled this option requires an input parameter



``MeanVolume``. Derefinement is then disallowed during the



run for all cells with ``Volume > 0.1 * MeanVolume``.













**OPTIMIZE_MESH_MEMORY_FOR_REFINEMENT**






If activated some grid structures not needed for mesh refinement/derefinement



are freed before the function for refinement and derefinement is called. The



remaining mesh structures are freed after this step as usual.













Nonstandard phyiscs



====================






**COOLING**






Simple primordial cooling routine.













**ENFORCE_JEANS_STABILITY_OF_CELLS**






This imposes an adaptive floor for the temperature.













**USE_SFR**






Star formation model, turning dense gas into collisionless partices. See



Springel&Hernquist, (2003, MNRAS, 339, 289)













**SFR_KEEP_CELLS**






Do not distroy cell out of which a star has formed.













Gravity



=================






If nothing is active, no gravity included.






**SELFGRAVITY**






Gravitational intraction between simulation particles/cells.













**HIERARCHICAL_GRAVITY**






Uses hierarchical splitting of the time integration of the gravity.













**CELL_CENTER_GRAVITY**






Uses geometric centers (instead of meshgenerating points) to calculate



gravity of cells, only possible with ``HIERARCHICAL_GRAVITY``.













**NO_GAS_SELFGRAVITY**






Switches off gas selfgravity in tree.













**GRAVITY_NOT_PERIODIC**






Gravity is not treated periodically.













**ALLOW_DIRECT_SUMMATION**






Performes direct summation instead of treebased gravity if number of active



particles < ``DIRECT_SUMMATION_THRESHOLD`` (= 3000 unless specified differently)













**DIRECT_SUMMATION_THRESHOLD=1000**






Overrides maximum number of active particles for which direct summation is



performed instead of tree based calculation.













**EXACT_GRAVITY_FOR_PARTICLE_TYPE=4**






Nsquared fashion gravity for a small number of particles of the given type.













**EVALPOTENTIAL**






When this option is set, the code will compute the gravitational potential



energy each time a global statistics is computed. This can be useful for



testing global energy conservation.













**RANDOMIZE_DOMAINCENTER**






Random displacement to position of domain center; avoids correlated



forceerrors, important mainly for isolated systems (which otherwise might



start to drift in some direction).













TreePM



==============






If no switch is active: no ParticleMesh calculation.






**PMGRID=512**






Dimension of particlemesh grid covering the domain.



This enables the TreePM method, i.e. the longrange force is computed with a



PMalgorithm, and the short range force with the tree. The parameter has to be



set to the size of the mesh that should be used, e.g. 256, 512, 1024 etc. The



mesh dimensions need not necessarily be a power of two, but the FFT is fastest



for such a choice. Note: If the simulation is not in a periodic box, then



a FFT method for vacuum boundaries is employed, using a mesh with dimension



twice that specified by ``PMGRID``. Should not be used with ``PMGRID<256``



because if this is active, the treeforce will be calculated assuming



nonperiodic boundary conditions. This approximation is only valid if the



range of the tree calculation is small compared to the box size.













**ASMTH=1.25**






This factor expressed the adopted force split scale in the TreePM approach in



units of the grid cell size. Setting this value overrides the default value of



1.25, in meshcells, which defines the longrange/shortrange force split.













**RCUT=6.0**






This determines the maximum radius, in units of the force split scale, out to



which the tree calculation in TreePM mode considers tree nodes. If a tree node



is more distant, the corresponding branch is discarded. The default value is



4.5, given in meshcells.













**PM_ZOOM_OPTIMIZED**






This option enables a different communication algorithm in the PM calculations



which works well independent of the data layout, in particular it can cope



well with highly clustered particle distributions that occupy only a small



subset of the total simulated volume. However, this method is a bit slower



than the default approach (used when the option is disabled), which is best



matched for homogenously sampled periodic boxes.













**PLACEHIGHRESREGION=2**






If this option is set (will only work together with ``PMGRID``), then the long



range force is computed in two stages: One Fouriergrid is used to cover the



whole simulation volume, allowing the computation of the largescale force.



A second Fourier mesh is placed on the region occupied by "highresolution"



particles, allowing the computation of an intermediatescale force. Finally,



the force on very small scales is computed by the tree. This procedure can be



useful for "zoomsimulations", where the majority of particles (the highres



particles) are occupying only a small fraction of the volume. To activate this



option, the parameter needs to be set to an integer that encodes the particle



types that make up the highres particles in the form of a bit mask. For



example, if types 0, 1, and 4 are the highres particles, then the parameter



should be set to ``PLACEHIGHRESREGION=1+2+16``, i.e. to the



sum 2^0+2^1+2^4. The spatial region covered by the highres grid is



determined automatically from the initial conditions. The region is



recalculated if one of the selected particles is falling outside of the



highresolution region. Note: If a periodic box is used, the highres zone is



not allowed to intersect the box boundaries.













**ENLARGEREGION=1.1**






This is only relevant when ``PLACEHIGHRESREGION`` is activated. The size of



the high resolution box will be automatically determined as the minimum size



required to contain the selected particle type(s), in a "shrinkwrap" fashion.



This region is be expanded on the fly, as needed. However, in order to prevent



a situation where this size needs to be enlarged frquently, such as when the



particle set is (slowly) expanding, the minimum size is multiplied by the



factor ``ENLARGEREGION`` (if defined). Then even if the set is expanding, this



will only rarely trigger a recalculation of the high resolution mesh geometry,



which is in general also associated with a change of the force split scale.













**GRIDBOOST=2**






Normally, if ``PLACEHIGHRESREGION`` is enabled, the code will try to offer an



effective grid size for the highresolution patch that is equivalent to



``PMGRID``. Because zeropadding has to be used for the highres inset, this



gives a total mesh twice as large, which corresponds to ``GRIDBOOST=2``. This



value can here be increased by hand, to e.g. 4 or 8, to increase the



resolution of the highres PM grid. The total mesh size used for the



highresolution FFTs is given by ``GRIDBOOST*PMGRID``.
















**FFT_COLUMN_BASED**






When this is enabled, the FFT calculations are not parallelized in terms of a



slabdecomposition but rather through a column based approach. This scales to



larger number of MPI ranks but is slower in absolute terms as twice as many



transpose operations need to be performed. It is hence only worthwhile to use



this option for very large number of MPI ranks that exceed the 1D mesh



dimension.













Gravity softening



=================






In the default configuration, the code uses a small table of possible



gravitational softening lengths, which are specified in the parameterfile



through the ``SofteningComovingTypeX`` and ``SofteningMaxPhysTypeX`` options,



where X is an integer that gives the "softening type". Each particle type is



mapped to one of these softening types through the



``SofteningTypeOfPartTypeY`` parameters, where ``Y`` gives the particle type.



The number of particle types and the number of softening types do not



necessarily have to be equal. Several particle types can be mapped to the same



softening if desired.






**NSOFTTYPES=4**






This can be changed to modify the number of available softening types. These



must be explicitly input as SofteningComovingTypeX parameters, and so the



value of ``NSOFTTYPES`` must match the number of these entries in the



parameter file.













**MULTIPLE_NODE_SOFTENING**






If the tree walk wants to use a 'softened node' (i.e. where the maximum



gravitational softening of some particles in the node is larger than the node



distance and larger than the target particle's softening), the node is opened



by default (because there could be mass components with a still smaller



softening hidden in the node). This can cause a subtantial performance penalty



in some cases. By setting this option, this can be avoided. The code will then



be allowed to use softened nodes, but it does that by evaluating the



nodeparticle interaction for each mass component with different softening



type separately (but by neglecting possible shifts in their centers of masses).



This also requires that each tree node computes and stores a vector with these



different masses. It is therefore desirable to not make the table of softening



types excessively large. This option can be combined with adaptive hydro



softening. In this case, particle type 0 needs to be mapped to softening type



0 in the parameterfile, and no other particle type may be mapped to softening



type 0 (the code will issue an error message if one doesn't obey to this).













**INDIVIDUAL_GRAVITY_SOFTENING=2+4**






The code can also be asked to set the softening types of some of the particle



types automatically based on particle mass. The particle types to which this



is applied are set by this compile time option through a bitmask encoding the



types. The code by default assumes that the softening of particle type 1



should be the reference. To this end, the code determines the average mass of



type 1 particles, and the types selected through this option then compute a



desired softening length by scaling the type1 softening with the cube root of



the mass ratio. Then, the softening type that is closest to this desired



softening is assigned to the particle (*choosing only from those softening



values explicitly input as a SofteningComovingTypeX parameter*). This option



is primarily useful for zoon simulations, where one may for example lump all



boundary dark matter particles together into type 2 or 3, but yet provide a



set of softening types over which they are automatically distributed according



to their mass. If both ``ADAPTIVE_HYDRO_SOFTENING`` and



``MULTIPLE_NODE_SOFTENING`` are set, the softening types considered for



assignment exclude softening type 0. Note: particles that accrete matter



(black holes or sinks) get their softening updated if needed.













**ADAPTIVE_HYDRO_SOFTENING**






When this is enabled, the gravitational softening lengths of hydro cells are



varied according to their radius. To this end, the radius of a cell is



multiplied by the parameter ``GasSoftFactor``. Then, the closest softening



from a logarithmicaly spaced table of possible softenings is adopted for the



cell. The minimum softening in the table is specified by the parameter



``MinimumComovingHydroSoftening``, and the larger ones are spaced a factor



``AdaptiveHydroSofteningSpacing`` apart. The resulting minimum and maximum



softening values are reported in the stdout log file.













**NSOFTTYPES_HYDRO=64**






This is only relevant if ``ADAPTIVE_HYDRO_SOFTENING`` is enabled and can be



set to override the default value of 64 for the length of the logarithmically



spaced softening table. The sum of ``NSOFTTYPES`` and ``NSOFTTYPES_HYDRO`` may



not exceed 254 (this is checked).













External gravity



================






By default, there is no external potential.






**EXTERNALGRAVITY**






Master switch for external potential.













**EXTERNALGY=0.0**






Constant external gravity in y direction













NFW Potential










**STATICNFW**






Static gravitational NavarroFrenkWhite (NFW) potential.













**NFW_C=12**






Concentration parameter of NFW potential.













**NFW_M200=100.0**






Mass causing the NFW potential.













**NFW_Eps=0.01**






Softening of NFW potential.













**NFW_DARKFRACTION=0.87**






Fraction in dark matter in NFW potential. Potential will be reduced by this



factor.













Isothermal Sphere










**STATICISO**






Static gravitational isothermal sphere potential.













**ISO_M200=100.0**






Mass causing the isothermal sphere potential.













**ISO_R200=160.0**






Radius of the isothermal sphere potential.













**ISO_Eps=0.1**






Softening of isothermal sphere potential.













**ISO_FRACTION=0.9**






Fraction in dark matter in isothermal sphere potential. Potential will be



reduced by this factor.













Hernquist Potential










**STATICHQ**






Static gravitational Hernquist potential.













**HQ_M200=186.015773**






Mass causing the Hernquist potential.













**HQ_C=10.0**






Concentration parameter of Hernquist potential.













**HQ_DARKFRACTION=0.9**






Fraction in dark matter in Hernquist potential. Potential will be reduced by



this factor.













Time integration



========================






**FORCE_EQUAL_TIMESTEPS**






Variable but global timestep.













**TREE_BASED_TIMESTEPS**






Nonlocal timestep criterion (take 'signal speed' into account).













**PM_TIMESTEP_BASED_ON_TYPES=2+4**






Particle types that should be considered in setting the PM timestep.













**NO_PMFORCE_IN_SHORT_RANGE_TIMESTEP**






PM force is not included in shortrange timestep criterion.













**ENLARGE_DYNAMIC_RANGE_IN_TIME**






This extends the dynamic range of the integer timeline from 32 to 64 bit













Message Passing Interface



========================================






**IMPOSE_PINNING**






Enforce pinning of MPI tasks to cores if MPI does not do it.













**IMPOSE_PINNING_OVERRIDE_MODE**






Override MPI pinning, if present.













Single/Double Precision



=======================






**DOUBLEPRECISION=1**






Mode of double precision: not set: single; 1: full double precision



2: mixed, 3: mixed, fewer single precisions; unless short of memory, use 1.













**DOUBLEPRECISION_FFTW**






FFTW calculation in double precision.













**OUTPUT_IN_DOUBLEPRECISION**






Snapshot files will be written in double precision.













**INPUT_IN_DOUBLEPRECISION**






Initial conditions are in double precision.













**OUTPUT_COORDINATES_IN_DOUBLEPRECISION**






Will always output coordinates in double precision.













**NGB_TREE_DOUBLEPRECISION**






If this is enabled, double precision is used for the neighbor node extension.













Groupfinder



========================================






**FOF**






Master switch to enable the friendsoffriends group finder code. This will



then usually be applied automatically before snapshot files are written



(unless disabled selectively for certain output dumps).













**FOF_PRIMARY_LINK_TYPES=2**






This option selects the particle types that are processed by the



friendsoffriends linking algorithm. A default linking length of 0.2 is



assumed for this particle type unless specified otherwise.



Sum(2^type) for the primary dark matter type.













**FOF_SECONDARY_LINK_TYPES=1+16+32**






With this option, FOF groups can be augmented by particles/cells of other



particle types that they "enclose". To this end, for each particle among the



types selected by the bit mask specifed with ``FOF_SECONDARY_LINK_TYPES``, the



nearest among ``FOF_PRIMARY_LINK_TYPES`` is found and then the particle is



attached to whatever group this particle is in. sum(2^type) for the types



linked to nearest primaries.













**FOF_SECONDARY_LINK_TARGET_TYPES= 2**






An option to make the secondary linking work better in zoom runs (after the



FOF groups have been found, the tree is newly constructed for all the



secondary link targets). This should normally be set to all dark matter



particle types. If not set, it defaults to ``FOF_PRIMARY_LINK_TYPES``, which



reproduces the old behaviour.













**FOF_GROUP_MIN_LEN=32**






Minimum number of particles (primary+secondary) in one group (default is 32).













**FOF_LINKLENGTH=0.16**






Linkinglength for FoF in units of the mean interparticle separation.



(default=0.2)













**FOF_FUZZ_SORT_BY_NEAREST_GROUP=0**






Sort fuzz particles by nearest group and generate offset table in catalog



(=1 writes nearest group number to snapshot).













**FOF_STOREIDS**






Normally, the snapshots produced with a FOF group catalogue are stored in



group order, such that the particle set making up a group can be inferred as a



contiguous block of particles in the snapsot file, making it redundant to



separately store the IDs of the particles making up a group in the group



catalogue. By activating this option, one can nevertheless force to create the



corresponding lists of IDs as part of the group catalogue output.













Subfind



===========================






**SUBFIND**






When enabled, this automatically runs the Subfind analysis of all FOF groups



after they have been found. This snapshot files are brought into subhalo order



within each group.













**SAVE_HSML_IN_SNAPSHOT**






When activated, this will store the hsmlvalues used for estimating total



matter density around every point and the corresonding densities in the



snapshot files associated with a run of Subfind.













**SUBFIND_CALC_MORE**






Additional calculations are carried out in the Subfind algorithm, which may be



expensive.



(i) The velocity dispersion in the local density estimate.



(ii) The DM density around every particle is stored in the snapshot if this is



set together with ``SAVE_HSML_IN_SNAPSHOT``.













**SUBFIND_EXTENDED_PROPERTIES**






Additional calculations are carried out, which may be expensive.



(i) Further quantities related to the angular momentum in different components.



(ii) The kinetic, thermal and potential binding energies for sperical



overdensity halos.
















Special behaviour



============================






**RUNNING_SAFETY_FILE**






If file './running' exists, do not start the run.













**MULTIPLE_RESTARTS**






Keep restart files instead of just last two copies.













**EXTENDED_GHOST_SEARCH**






This extends the ghost search to the full 3x3 domain instead of the principal



domain.













**DOUBLE_STENCIL**






This will ensure that the boundary region of the local mesh is deep enough to



have a valid double stencil for all local cells.













**TETRA_INDEX_IN_FACE**






Adds an index to each entry of VF[] and DC[] to one of the tetrahedra that



share this edge.













**NOSTOP_WHEN_BELOW_MINTIMESTEP**






Simulation does not terminate when timestep drops below minimum timestep.













**TIMESTEP_OUTPUT_LIMIT**






Limits timesteps to write snaps on time for frequent outputs.













**ALLOWEXTRAPARAMS**






Tolerate extra parameters that are not used.













**FIX_SPH_PARTICLES_AT_IDENTICAL_COORDINATES**






This can be used to load SPH ICs that contain identical particle coordinates.













**RECOMPUTE_POTENTIAL_IN_SNAPSHOT**






Needed for postprocess option 18 that can be used to calculate potential



values for a snapshot.













**ACTIVATE_MINIMUM_OPENING_ANGLE**






This does not open tree nodes under the relative opening criterion any more



if their opening angle has dropped below a minimum angle.













**USE_DIRECT_IO_FOR_RESTARTS**






Try to use O_DIRECT for lowlevel read/write operations of restart files to



circumvent the linux kernel page caching.













**HUGEPAGES**






Use huge pages for memory allocation, through hugetlbfs library.













**DETAILEDTIMINGS**






Creates individual timings entries for primary/secondary kernels to diagnose



workload balancing.













**BITS_PER_DIMENSION=42**






Bits per dimension used in PeanoHilbert key. (default: 42)
















Input options



=============






**COMBINETYPES**






Reads in the IC file types 4+5 as type 3.













**LOAD_TYPES=1+2+4+16+32**






Load only specific types sum(2^type).













**READ_COORDINATES_IN_DOUBLE**






Read coordinates in double precision.













**LONGIDS**






If this is set, the code assumes that particleIDs are stored as 64bit long



integers. This is only really needed if you want to go beyond ~2 billion



particles.













**OFFSET_FOR_NON_CONTIGUOUS_IDS**






Determines offset of IDs on startup instead of using fixed offset.













**GENERATE_GAS_IN_ICS**






Generates gas from dark matter only ICs (using particle type 1 by default).













**SPLIT_PARTICLE_TYPE=4+8**






Overrides splitting particle type 1 in ``GENERATE_GAS_IN_ICS`` use sum(2^type).













**SHIFT_BY_HALF_BOX**






Shift all positions by half a box size after reading in.













**NTYPES_ICS=6**






Number of particle types in ICs, if not ``NTYPES``.













**READ_MASS_AS_DENSITY_IN_INPUT**






Reads the mass field in the IC as density.













Special input options



=====================






**IDS_OFFSET=1**






Override offset for gas particles if created from DM.













**READ_DM_AS_GAS**






Reads in dark matter particles as gas cells.













**TILE_ICS**






Tile ICs by TileICsFactor (specified as paramter) in each dimension.













Output fields



==========================






Default output filds are: ``position``, ``velocity``, ``ID``, ``mass``,



``specific internal energy`` (gas only), ``density`` (gas only)






**OUTPUT_TASK**






Output of MPI task.













**OUTPUT_TIMEBIN_HYDRO**






Output of hydrodynamics timebin.













**OUTPUT_PRESSURE_GRADIENT**






Output of pressure gradient.













**OUTPUT_DENSITY_GRADIENT**






Output of density gradient.













**OUTPUT_VELOCITY_GRADIENT**






Output of velocity gradient.













**OUTPUT_BFIELD_GRADIENT**






Output of magnetic field gradient.













**OUTPUT_MESH_FACE_ANGLE**






Output of maximum face angle of cells.













**OUTPUT_VERTEX_VELOCITY**






Output of velocity of meshgenerating point.













**OUTPUT_VOLUME**






Output of volume of cells; note that this can always be computat as both, density



and mass of cells are by default in output.













**OUTPUT_CENTER_OF_MASS**






Output of center of mass of cells (``Pos`` is position of meshgenerating point).













**OUTPUT_SURFACE_AREA**






Output of surface area of cells as well as the number of faces.













**OUTPUT_PRESSURE**






Output of pressure of gas.













**OUTPUTPOTENTIAL**






This will force the code to compute gravitational potentials for all particles



each time a snapshot file is generated. These values are then included in the



snapshot files. Note that the computation of the values of the potential costs



additional time.













**OUTPUTACCELERATION**






Output of gravitational acceleration.













**OUTPUTTIMESTEP**






Output of timestep of particle.













**OUTPUT_SOFTENINGS**






Output of particle softenings.













**OUTPUTGRAVINTERACTIONS**






Output of gravitatational interactions (from the gravitational tree) of particles.













**OUTPUTCOOLRATE**






Output of cooling rate.













**OUTPUT_DIVVEL**






Output of velocity divergence.













**OUTPUT_CURLVEL**






Output of velocity curl.













**OUTPUT_COOLHEAT**






Output of actual energy loss/gain in cooling/heating routine.













**OUTPUT_VORTICITY**






Output of vorticity of gas.













**OUTPUT_CSND**






Output of sound speed. This field is only used for treebased timesteps!



Calculate from hydro quantities in postprocessing if required for science



applications.













Output options



==============






**PROCESS_TIMES_OF_OUTPUTLIST**






Goes through times of output list prior to starting the simulaiton to ensure



that outputs are written as close to the desired time as possible (as opposed



to at next possible time if this flag is not active).













**REDUCE_FLUSH**






If enabled files and stdout are only flushed after a certain time defined in



the parameter file (standard behaviour: everything is flashed most times



something is written to it).













**OUTPUT_EVERY_STEP**






Create snapshot on every (global) synchronization point, independent of



parameters choosen or output list.













**OUTPUT_CPU_CSV**






Output of a cpu.csv file on top of cpu.txt.













**HAVE_HDF5**






If this is set, the code will be compiled with support for input and output in



the HDF5 format. You need to have the HDF5 libraries and headers installed on



your computer for this option to work. The HDF5 format can then be selected as



format "3" in Arepo's parameterfile.













**HDF5_FILTERS**






Activate snapshot compression and checksum for HDF5 output.













**OUTPUT_XDMF**






Writes an ``.xmf`` file for each snapshot, which can be read by visit



(with the hdf5 snapshot). Note: so far only working if the snapshot



is stored in one file.













Testing and Debugging



=============================






**DEBUG**






Enables coredumps.













**VERBOSE**






Reports readjustments of buffer sizes.













Regridding



============================






These opitions are auxiliary modes to prepare/convert/relax initial conditions



and will not carry out a simulation.






**MESHRELAX**






This keeps the mass constant and only regularizes the mesh.













**ADDBACKGROUNDGRID=16**






Regrid hydrodynamics quantities on a Octtree AMR grid. This does not perform



a simulation. This "converts" an SPH initial condition into a (moving) mesh



initial condition. 