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Output inventory, plotting, and budget analysis

Analyze without overclaiming

Output analysis can detect errors and quantify diagnostics. It cannot by itself establish:

• Correct equations, units, or boundary/initial/forcing conditions.
• Adequate resolution or dealiasing.
• Stable/accurate time integration.
• Conservation or budget closure.
• Statistical stationarity.
• Grid/time convergence.
• Physical validity.

Keep plotting descriptive until those checks pass.

FluidSim 0.9 physical-state format

Official 0.9 source selects:

• .nc with h5netcdf when h5py lacks MPI support (normal default).
• .h5 with h5py when h5py is MPI-enabled.

Filename:

state_phys_t<TIME>[_it<ITERATION>].nc

or .h5, depending on the backend. The file is HDF5-backed in either current path. It contains:

• /state_phys: solver state datasets.
• /state_phys attributes including time, it, variable type, and purpose.
• /info_simul: solver and parameter provenance.
• Saved state parameters when available, including restart-relevant forcing state in 0.9.
• Root attributes such as run/solver identity, axes, and save date.

Do not infer the latest valid checkpoint solely from a filename. Verify HDF5 readability, /state_phys, time/iteration attributes, expected datasets, parameters, state parameters, size, and checksum.

Other common outputs

Exact outputs depend on the solver and enabled classes.

Spatial means

• Legacy/solver-specific: spatial_means.txt, generally repeated key = value records.
• Some output classes use spatial_means.json, JSON-lines records.
• Typical content can include time, energy/enstrophy, forcing power, dissipation, and solver-specific quantities.

Use the solver's load() implementation. It can return a dictionary, pandas object, or another solver-specific structure; do not assume one universal DataFrame schema.

Spectra

Current 2D base spectra initialize:

spectra1D.h5
spectra2D.h5

Common datasets include:

• times
• kxE, kyE, or khE
• solver-specific spectrum1D* or spectrum2D* arrays

NS2D/NS3D and stratified variants define different keys and dimensions. load1d_mean()/load2d_mean() return dictionaries in the base implementation; inspect keys before use.

Spectral energy budget

The current base filename is:

spect_energy_budg.h5

For NS2D, current source computes transfer2D_E and transfer2D_Z and derives fluxes with a reverse cumulative sum multiplied by wave-number spacing. Other solvers define different transfer/budget terms.

Do not interpret a transfer sign, flux plateau, or cascade without verifying:

• Fourier/spectrum normalization.
• Wave-number coordinate and shell/bin measure.
• Sign convention.
• Time averaging interval and stationarity.
• Forcing/dissipation ranges.
• Finite-domain and dealiased cutoff effects.
• Closure against the corresponding global budget.

Logs and parameter files

A normal run may include:

• params_simul.xml
• info_solver.xml
• stdout.txt
• a run lock while advancing
• solver/output-specific HDF5, netCDF4, text, or JSON files

Inventory actual contents instead of assuming all files exist.

Bounded metadata inventory

python3 scripts/output_inventory.py \
  --path run-directory \
  --max-files 256 \
  --max-hdf5-files 32 \
  --max-datasets 2000 \
  --max-attributes 5000

The helper:

• Accepts only local paths inside --root.
• Rejects URLs, parent traversal, symlinks, hard links, special files, and unbounded counts.
• Lazily imports h5py only for HDF5/netCDF4 candidates.
• Reports dataset shape, dtype, chunks, compression, and allocated storage.
• Reads only a short allowlist of scalar provenance attributes.
• Does not index datasets.
• Does not follow soft or external HDF5 links.
• Emits strict JSON and no raw field values.

If a .nc file is classic netCDF rather than HDF5, it reports it unreadable rather than trying another unbounded parser.

Read-only FluidSim object

from fluidsim import load_sim_for_plot

sim = load_sim_for_plot(
    "run-directory",
    merge_missing_params=False,
    hide_stdout=True,
)

Official 0.9 source uses a coarse operator and disables saving/online plots. This is appropriate for output-class analysis, not full-resolution arbitrary field operations.

Examples:

sim.output.phys_fields.plot(time=1.0)
sim.output.spatial_means.plot()
sim.output.spectra.plot1d(tmin=0.5, tmax=1.0)
sim.output.spect_energy_budg.plot(tmin=0.5, tmax=1.0)

Methods and accepted arguments vary by solver/output class. Check the selected class API. A successful plot says nothing about correctness.

Full state loading

from fluidsim import load_state_phys_file

sim = load_state_phys_file(
    "run-directory",
    t_approx="last",
    modif_save_params=True,
    merge_missing_params=False,
    init_with_initialized_state=True,
    hide_stdout=True,
)

This can allocate full-resolution state/operators. Run the memory estimator first and do not use it merely to inspect metadata.

modif_save_params=True disables saving/online plotting. To continue a run, use the reviewed restart workflow rather than toggling saving casually.

Scalar and spectral summary helper

python3 scripts/budget_summary.py \
  --path run-directory \
  --max-files 128 \
  --max-records 200000 \
  --max-datasets 256 \
  --max-values-per-dataset 4096

It:

• Aggregates finite spatial-mean values in constant memory.
• Supports FluidSim key/value text and strict JSON-lines.
• Summarizes only bounded spectral/budget hyperslabs.
• Uses the latest first-axis record for multidimensional datasets.
• Emits a sum only when the entire latest record fits the value bound.
• Does not follow external links or load full large arrays.
• Explicitly reports that convergence/physical validity are not established.

This is a triage summary, not a solver-aware closure calculation.

Budget checks

Construct a table or plot for each governing budget:

1. Stored quantity change over the same interval.
2. Measured forcing/input.
3. Physical and numerical dissipation.
4. Transfer terms with consistent sign/normalization.
5. Boundary terms (zero only if justified by periodicity/model).
6. Residual after all terms.

Report absolute and normalized residuals, time interval, differencing method, save cadence, and uncertainty. A small instantaneous residual can be accidental; inspect trends and refinement.

For forced turbulence, compare requested forcing_rate to measured forcing power. They are not interchangeable without checking the implementation's normalization and time discretization.

Resolution and dealiasing diagnostics

At minimum:

• Plot/inspect spectra up to the dealiased cutoff.
• Quantify energy/variance in a documented high-wave-number tail band.
• Check pile-up, aliasing signatures, anisotropy, and directional spectra where relevant.
• Check physical-space extrema/gradients and solver constraints.
• Repeat at finer resolution with the same physical/nondimensional problem.
• Avoid choosing an “inertial range” after seeing the desired slope without reporting selection criteria and sensitivity.

Power-law fitting alone does not verify a cascade or resolved simulation.

Time-step diagnostics

Use stdout/output time-step history to inspect:

• Initial and maximum deltat.
• CFL-driven changes.
• Fast-wave or buoyancy/rotation scales.
• Diffusive/hyperdiffusive limits.
• Discontinuities around restart.
• Sensitivity to lower deltat_max/cfl_coef.

Do not infer stability from the absence of NaNs.

Stationarity and averaging

Before time averaging:

• Define stationarity metrics and burn-in independently of the desired result.
• Plot energy, dissipation, forcing, and key observables.
• Check drift and autocorrelation/integral times.
• Report effective sample duration/count.
• Repeat across seeds or independent intervals where stochastic uncertainty matters.

Do not label “statistically steady” from a short visual plateau.

Custom HDF5 reading

If built-in loaders are insufficient, keep access bounded:

import h5py

with h5py.File("spectra2D.h5", "r") as handle:
    dataset = handle["spectrum2D_E"]
    latest = dataset[-1, :4096]

Before indexing, inspect shape, dtype, chunks, and expected bytes. Never use dataset[...] or [:] on an unknown large field. Check HDF5 links before traversal; an external link can open another file.

Plot/report provenance

Every exported result should carry:

• Parent run/config/script/lock hashes.
• Solver and package/backend versions.
• Grid/domain/dealiasing/time scheme/CFL.
• Initial/forcing/dissipation definitions.
• State/output file hashes or immutable manifest.
• Exact dataset keys and time window.
• Averaging/binning/normalization and plotting code revision.
• Refinement and budget-check results.

Avoid manual GUI-only transformations that cannot be reconstructed.

Sources (verified 2026-07-23)

• Physical-field save source — .nc/.h5 selection, groups, attributes, state parameters, filename.
• Physical-fields output source.
• Spatial-means source.
• Spectra source.
• Spectral-budget base source.
• NS2D spectral-budget source.
• Load utilities.
• Mohanan et al., FluidSim primary paper, published 2019-04-26 — architecture and output-class method claims.