Visualisation

A set of Python scripts is provided for live-playback visualisation of simulation output. They are driven by the scripts/qaxi shell wrapper, which selects the correct plot script and forwards arguments.

Quick Start

./bin/qaxi [TYPE] [DATA_DIR] [PAUSE]

Argument	Default	Description
`TYPE`	`dens`	Plot type: `dens` (density field) or `spec` (power spectrum)
`DATA_DIR`	`output`	Directory containing simulation output files
`PAUSE`	`0.1`	Pause between frames in seconds (controls playback speed)

Plot Types

`dens` — Density Field

./bin/qaxi dens output 0.1

Reads field_*.h5 files from DATA_DIR and animates the projected density field frame by frame.

Requires the field output to be enabled at run time:

./qaxions --meas 8

What is plotted:

For 3D simulations, the density field is averaged along the first axis to produce a 2D projection. The plotted quantity is the log-density contrast:

\[\log_{10}\!\left(\rho / \langle\rho\rangle\right)\]

HDF5 file layout expected:

Path	Description
`/rho/data`	Density array
`Header` attrs `N`, `dim`, `a`	Grid size, dimension, scale factor

`spec` — Power Spectrum

./bin/qaxi spec output 0.05

Reads spec_*.txt files from DATA_DIR and animates the dimensionless power spectrum $\Delta^2_k$ as a function of wavenumber $k$.

Requires spectrum output to be enabled at run time:

./qaxions --meas 1

What is plotted:

The dimensionless power spectrum, defined as:

\[\Delta^2_k = \frac{k^2 \, P(k)}{2\pi^2}\]

Both axes are logarithmic. The initial condition spectrum is overplotted as a fixed black reference line. The current spectrum is shown in blue and the title tracks the scale factor $a$.

Text file format expected:

Each spec_*.txt file must have a header comment of the form:

# a: <value>

followed by three whitespace-separated columns:

k Wavenumber
P Power spectrum
counts Bin counts

Dependencies

The visualisation scripts require the following Python packages:

pip install h5py numpy matplotlib cmasher

A custom Matplotlib style sheet is expected at scripts/sty.mplstyle. Without it the scripts will raise a warning but will still run using the default style.

Tips

Slow down or speed up playback by adjusting the PAUSE argument:

./bin/qaxi dens output 0.5   # slower
./bin/qaxi dens output 0.01  # faster

Replay after the run — the scripts work equally well on completed runs as on live output, since they simply iterate over sorted file lists.

Enabling both outputs simultaneously requires combining the --meas flags. See the Usage page for the full list of measurement flags.