Output and light-cone settings

See also Output and post-processing.

Paths, names, and schedules

Parameter	Default	Behaviour
output path	current directory	Existing output directory; gevolution does not create it.
generic file base	empty	Prefix for background, used-settings, and diagnostic files.
snapshot file base	snapshot	Snapshot prefix.
Pk file base	pk	Power-spectrum prefix.
lightcone file base	lightcone	Light-cone prefix.
snapshot redshifts	none	Snapshot schedule.
Pk redshifts	none	Power-spectrum schedule.
Pk bins	64	Requested number of spectrum bins.

Redshift lists are sorted into descending order. Output is normally written on the first integration cycle after the requested redshift has been passed; the time step is not adapted to hit scheduled redshifts.

With EXACT_OUTPUT_REDSHIFTS, power spectra can be interpolated to the target redshift and Gadget-2 particle snapshots shift particle positions to the target time. Field snapshots remain tied to an integration step.

Output specifiers

snapshot outputs, Pk outputs, and lightcone outputs accept comma-separated specifiers. Recognised aliases include:

Specifier	Quantity or format	Important restrictions
phi, chi, B, hij	Metric fields	Metric light cones require HAVE_HEALPIX.
T00, Tij, p	Stress-energy fields	Snapshot T00, Tij, and p are totals, not per-species fields. Tij and p are not spectrum choices.
rhoN, psiN, delta, deltaN	Newtonian density/potential and density contrasts	delta and deltaN are spectrum normalisations rather than field snapshots.
v or velocity	Coarse-grained velocity	Requires VELOCITY. Spectrum output also writes divergence and curl products.
pcls	LATfield2/HDF5 particle output	Current GPU snapshot path only writes enabled non-CDM HDF5 particle datasets; prefer Gadget-2 for general particle snapshots.
Gadget2	Single-file Gadget-2 particle snapshots	Subject to the Gadget single-file particle-count limit.
multi-Gadget2	Split Gadget-2 particle snapshots	CDM and baryons write one file per MPI rank; non-CDM species use one file per rank in process-grid dimension 1 (m). Validate this mixed layout with downstream tools.
X-spectra	Additional species cross-spectra	CDM-baryon and all requested non-CDM cross-pairs are added.

Even without X-spectra, non-CDM pairs 0x1, 2x3, and 4x5 are produced when those species exist, supporting paired-species shot-noise suppression. Empty spectrum bins are omitted.

T00 and rhoN spectra use proper-density-squared normalisation. delta and deltaN are the corresponding dimensionless density contrasts. Velocity divergence and curl spectra have inverse-length-squared dimensions.

Particle and field reduction

tracer factor

This per-species list controls Gadget-2 snapshots and particle light cones. Only IDs divisible by the factor are retained; 1 writes all particles and 0 omits the species. Negative values are corrected to 1. The operation is lossy, and the written particle mass is increased consistently.

For crystal templates, the following factors preserve a crystal subset:

Template	Crystal-preserving factors
Simple cubic	1, 2, 8, 16, 64
Face-centred cubic	1, 4, 8, 32
Body-centred cubic	1, 2, 4, 16

downgrade factor

Field snapshots average each block of (downgrade factor)^3 mesh vertices. The factor must be positive, smaller than Ngrid, and divide each decomposed local domain. It never applies to particle snapshots.

Light-cone geometry

A non-enumerated parameter supplies defaults or defines one light cone:

lightcone outputs = Gadget2, phi
lightcone vertex = 0, 0, 0

For multiple geometries, use lightcone 0 ..., lightcone 1 ..., and so on. Unnumbered output, Nside, pixel, shell, and covering settings become defaults for enumerated cones. Enumeration starts at zero and parsing stops at the first missing or invalid numbered vertex.

Parameter	Default	Behaviour
lightcone vertex	no cone	Three observer coordinates in Mpc/h; each must lie in [0, boxsize).
lightcone redshift	0	Observation redshift.
lightcone distance	0, boxsize/2	One value gives outer distance with inner distance zero; two values are sorted into outer and inner distances.
lightcone opening half-angle	full sky	Degrees in (0, 180]; invalid values warn and select full sky.
lightcone direction	0, 0, 1	Either polar angles \((\theta,\phi)\) in degrees or a non-zero three-component Cartesian vector, which is normalised.
lightcone Nside	2 to first power of two at least Ngrid	One value fixes resolution; two give minimum and maximum. Values are at least 2, at most 16384, and non-powers of two round upward.
lightcone pixel factor	0.5	Chooses angular sampling relative to mesh resolution.
lightcone shell factor	1	Number of radial shells per mesh spacing.
lightcone covering	2 + 4 / (Courant factor * shell factor)	Temporal overlap of pixelised metric shells. It has no effect on particle data.

Pixel, shell, and covering factors must be finite and strictly positive. Cartesian directions must have a finite, non-zero norm. Distances must be finite, non-negative, and ordered from outer to inner radius.

The pixel resolution is chosen as the smallest allowed Nside satisfying

\[ (\mathtt{pixel\ factor}) A_\mathrm{pix} < \Delta x^2. \]

Covering greater than one repeats metric shells across cycles, enabling time derivatives in post-processing. Particle light cones use Gadget-2 output. Metric light cones can contain phi, chi, B, and hij and require HAVE_HEALPIX.

Particle-ID consistency logs are shared between enumerated cones with the same vertex and observation redshift.