Provenance (reproducibility)

Six months after you make a figure, the question is always the same: which snapshot, which Mera version, what units produced this? provenance answers it. It reads the metadata every Mera result already carries (its InfoType) and returns a compact, deterministic record. You can print it, compare it in a test, or put it on a figure or into a log.

# Example-data root. Point this at your own simulation folder, or set the
# MERA_EXAMPLES environment variable; every path below is built from it.
MERA_EXAMPLES = get(ENV, "MERA_EXAMPLES", "/Volumes/FASTStorage/Simulations/Mera-Tests");

using Mera
info = getinfo(300, joinpath(MERA_EXAMPLES, "RAMSES/mw_L10"))

# The loading messages add nothing on this page, so the data reads below are quiet.
gas = gethydro(info, verbose=false, show_progress=false);

*__   __ _______ ______   _______
|  |_|  |       |    _ | |   _   |
|       |    ___|   | || |  |_|  |
|       |   |___|   |_||_|       |
|       |    ___|    __  |       |
| ||_|| |   |___|   |  | |   _   |
|_|   |_|_______|___|  |_|__| |__|
Mera v1.8.0 | Julia 1.12.7 | 4 threads
[Mera]: 2026-09-17T16:27:17.273
Code: RAMSES
output [300] summary:
mtime: 2023-04-09T05:34:09
ctime: 2025-06-21T18:31:24.020
=======================================================
simulation time: 445.89 [Myr]
boxlen: 48.0 [kpc]
ncpu: 640
ndim: 3
cosmological:  false
-------------------------------------------------------
amr:           true
level(s): 6 - 10 --> cellsize(s): 750.0 [pc] - 46.88 [pc]
-------------------------------------------------------
hydro:         true
hydro-variables:  7  --> (:rho, :vx, :vy, :vz, :p, :scalar_00, :scalar_01)
hydro-descriptor: (:density, :velocity_x, :velocity_y, :velocity_z, :pressure, :scalar_00, :scalar_01)
γ: 1.6667
-------------------------------------------------------
gravity:       true
gravity-variables: (:epot, :ax, :ay, :az)
-------------------------------------------------------
particles:     true
- Nstars:   5.445150e+05
particle-variables: 7  --> (:vx, :vy, :vz, :mass, :family, :tag, :birth)
particle-descriptor: (:position_x, :position_y, :position_z, :velocity_x, :velocity_y, :velocity_z, :mass, :identity, :levelp, :family, :tag, :birth_time)
-------------------------------------------------------
rt:            false
clumps:           false
-------------------------------------------------------
namelist-file: ("&COOLING_PARAMS", "&SF_PARAMS", "&AMR_PARAMS", "&BOUNDARY_PARAMS", "&OUTPUT_PARAMS", "&POISSON_PARAMS", "&RUN_PARAMS", "&FEEDBACK_PARAMS", "&HYDRO_PARAMS", "&INIT_PARAMS", "&REFINE_PARAMS")
-------------------------------------------------------
boundaries:       not periodic (&BOUNDARY_PARAMS closes x, y, z)
timer-file:       true
compilation-file: false
makefile:         true
patchfile:        true
=======================================================

The record

provenance(obj) returns a Provenance struct. Printed, it is a short block with the Mera version, the simulation and output (and the code that wrote it), the snapshot time, the box and level range, and the scale type.

p = provenance(gas)
println(p)

Provenance:
  Mera version : v1.8.0
  simulation   : /Volumes/FASTStorage/Simulations/Mera-Tests/RAMSES/mw_L10
  output       : 300  (RAMSES, written 2025-06-21T18:31:24.020)
  time         : 445.89 Myr
  box / levels : L=48.0  ndim=3  levels 6–10
  scale type   : ScalesType003

Which build ran

pkgversion reports the same version whether Mera came from the registry or from a checkout of a branch. A result made on a development version would then look like it was made on the release. mera_build closes that gap, and its value is the version field of every record.

mera_build()

"1.8.0"

On a normal install it is just the version, as above. On a git checkout it adds the branch and the commit. It also marks a working tree with uncommitted changes, because then the commit alone does not say what ran:

Mera v1.8.0 (dev master @ 3a91f2c) | mw_L10/output_00300 | 445.89 Myr | ...
Mera v1.8.0 (dev my-feature @ 4f2a9c1 +uncommitted) | mw_L10/output_00300 | 445.89 Myr | ...

This keeps a shared script honest about what produced it. The Gallery uses the same line in its attribution block, so a reader can tell a released Mera from somebody's branch.

Set MERA_PROVENANCE_PLAIN=1 to force the plain version. These pages are rendered that way, so they show a release rather than the checkout the documentation was built from.

What it records

Every field is read from the snapshot's own metadata, plus the Mera build:

for f in fieldnames(Provenance)
    println(rpad(f, 13), "= ", repr(getfield(p, f)))
end

mera_version = v"1.8.0"
mera_build   = "1.8.0"
path         = "/Volumes/FASTStorage/Simulations/Mera-Tests/RAMSES/mw_L10"
output       = 300
simcode      = "RAMSES"
cosmological = false
time_myr     = 445.8861174695
redshift     = 0.0
aexp         = 1.0
boxlen       = 48.0
ndim         = 3
levelmin     = 6
levelmax     = 10
scale_type   = :ScalesType003
file_ctime   = Dates.DateTime("2025-06-21T18:31:24.020")

Cosmological runs

For a normal run the time is physical, in Myr or Gyr. For a cosmological run the record shows the redshift, with the expansion factor and the age of the universe. iscosmological tells which case you have. The galaxy above is not cosmological, so here is one of the test simulations that is. Only its metadata is read.

cinfo = getinfo(80, joinpath(MERA_EXAMPLES, "RAMSES/yt_cosmo"), verbose=false)
pc = provenance(cinfo)
println(pc)
println()
println("iscosmological : ", iscosmological(cinfo), "   (the galaxy: ", iscosmological(info), ")")
println("redshift       : ", pc.redshift)
println("aexp           : ", pc.aexp)

Provenance:
  Mera version : v1.8.0
  simulation   : /Volumes/FASTStorage/Simulations/Mera-Tests/RAMSES/yt_cosmo
  output       : 80  (RAMSES, written 2026-06-01T07:42:48.561)
  time         : z=0.1426  (aexp=0.8752, age 11.925 Gyr)
  box / levels : L=1.0  ndim=3  levels 6–16
  scale type   : ScalesType003
iscosmological : true   (the galaxy: false)
redshift       : 0.14255728632206321
aexp           : 0.875229637910795

Stamping a figure or a log

provenance_string gives the record as one line. Put it in a figure caption, a log file or the header of a file you write. The time is in Myr or Gyr, or z=… for a cosmological run.

println(provenance_string(gas))
println(provenance_string(cinfo))

Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003
Mera v1.8.0 | yt_cosmo/output_00080 | z=0.14256 | L=1.0 ndim=3 lmin=6 lmax=16 | ScalesType003

Where it applies

provenance works on an InfoType and on every result that carries one in its .info field:

• every data object, and any subregion of one
• a projection map
• a pdf of a data object or a map
• a galaxy frame from face_on or edge_on

The record describes the snapshot, not the selection. A subregion, or a read of one variable up to a lower level, gives the same record as the full read.

println("InfoType   : ", provenance_string(gas.info))

sd = projection(gas, :sd, :Msol_pc2; center=[:bc], verbose=false, show_progress=false)
println("map        : ", provenance_string(sd))
println("pdf        : ", provenance_string(pdf(gas, :rho)))

parts = getparticles(info, verbose=false, show_progress=false)
println("particles  : ", provenance_string(parts))

# one variable up to level 8 is enough: the record still says levels 6 to 10
grav = getgravity(info, :epot, lmax=8, verbose=false, show_progress=false)
println("gravity    : ", provenance_string(grav))

InfoType   : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003
map        : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003
pdf        : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003
particles  : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003
gravity    : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003

A result without .info cannot know its snapshot: a profile or phase, a timeseries table, or a pdf of a plain array. provenance then throws an ArgumentError that says so. Take the provenance of the data object you computed it from.

prof = profile(gas, :r_cylinder, :rho; nbins=10, center=[:bc])
try
    provenance(prof)
catch err
    println(sprint(showerror, err))
end
println()
println("use the source instead : ", provenance_string(gas))

ArgumentError: provenance: a NamedTuple carries no `.info`. Apply it to a data object (hydro/particles/gravity/clumps/RT), a projection map, a pdf of either, a galaxy frame, or an InfoType. For a result without it (profile, phase, timeseries, a pdf of a plain array), take provenance of the source data object.
use the source instead : Mera v1.8.0 | mw_L10/output_00300 | 445.89 Myr | L=48.0 ndim=3 lmin=6 lmax=10 | ScalesType003

Deterministic

The record depends on the snapshot's own metadata and on the Mera build, never on the wall clock. Two independent reads of the same output give identical records, which makes the record safe to compare in a test.

# read the metadata of the same output again, from disk
p2 = provenance(getinfo(300, joinpath(MERA_EXAMPLES, "RAMSES/mw_L10"), verbose=false))
println("identical to the first read : ", p2 == p)

identical to the first read : true

See also

• getinfo, the InfoType the record is read from
• Reproducibility, how the record fits with a pinned project and test simulations
• MERA files, where the scale_type version matters when loading older files
• Gallery, which puts the provenance line in the attribution block of its recipes