# plotEigenWavespeed (file: eigenWavespeed.m)

Plots the **group/phase wave speed** `c_n = omega_n / k_n` of each damped
eigenmode as a function of its frequency `omega_n`. For every (pressure,
damping) combination in the data it: extracts the modes with positive
imaginary part, finds each mode's dominant wavenumber `k_n` by 2D-FFTing the
x-component of the eigenvector (interpolated onto a regular grid), then plots
`c_n` vs `omega_n` on log-log axes. Marker **color** encodes pressure, marker
**size** encodes damping.

> **Note 1:** The function is declared as `plotEigenWavespeed` inside the file
> `eigenWavespeed.m`. MATLAB requires the function name to match the filename,
> so the file must be renamed to `plotEigenWavespeed.m` (or the declaration
> changed) before it can be called.
>
> **Note 2:** This function depends on helpers from the parent project
> [GranMA](https://github.com/ColtonKawamura/GranMA) (`filterData`,
> `plotEigenmode`, `normVarColor`) — make sure that repo is on the MATLAB path.

## Default Syntax

```matlab
plotData = load("path/to/2D_damped_eigenstuff_....mat");  % outData struct from processEigenModesDampedPara
pressureList = [0.01 0.05 0.1];   % double vector, pressures in the data
dampingList = [0.001 0.01 0.03];  % double vector, dampings in the data
plotEigenWavespeed(plotData, pressureList, dampingList)
```

This plots `c_n` vs `omega_n` for all requested (pressure, damping)
combinations in one figure. Scalar lists are fine — a single pressure or a
single damping produces one curve (blue, fixed marker size).

## Arguments

| Arg | Type | Meaning |
|---|---|---|
| `plotData` | struct | `outData` struct (cells `eigenVectors`/`eigenValues`, columns `pressure`/`damping`/`positions`/`radii`/`Lx`/`Ly`/`springConstant`) |
| `pressureList` | double vector | Pressures to plot, must match values present in `plotData.pressure` |
| `dampingList` | double vector | Dampings to plot, must match values present in `plotData.damping` |

## Example

```matlab
outData = load('data/junkyard/2D_damped_eigenstuff_N400_20by20_K100_M1.mat').outData;

% Full sweep: 3 pressures x 3 dampings
plotEigenWavespeed(outData, [0.01 0.05 0.1], [0.001 0.01 0.03]);

% Single pressure, several dampings
plotEigenWavespeed(outData, 0.1, [0.001 0.01 0.03]);

% A couple of selected (P, gamma) pairs only
plotEigenWavespeed(outData, [0.01 0.1], [0.001 0.03]);
```

The FFT wavenumber estimate uses a fixed `0.1` grid spacing (hardcoded in the
function), so the reported `k_n` is a low-resolution estimate of the mode's
dominant wavevector.