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"""
02 — Plot the first 6 POD spatial mode shapes on the yz-mid plane.
Refits PCA with 6 components on the full dataset (the canonical model
in 01 only retains N_MODES=4, but for visualization we want a couple
extra modes to illustrate the diminishing structure).
"""
import numpy as np
import matplotlib.pyplot as plt
from sklearn.decomposition import PCA
from _utils import load_data, PLOTS_DIR
N_PLOT = 6
def main():
_, fields, coords, _ = load_data()
pca = PCA(n_components=N_PLOT).fit(fields)
var = pca.explained_variance_ratio_
y, z = coords[:, 1], coords[:, 2]
fig, axes = plt.subplots(3, 2, figsize=(8, 7))
for i, ax in enumerate(axes.flatten()):
mode = pca.components_[i]
vmax = np.abs(mode).max()
ax.scatter(z, y, c=mode, cmap="RdBu_r", s=1.5,
vmin=-vmax, vmax=vmax, rasterized=True)
ax.invert_xaxis()
ax.set_xticks([]); ax.set_yticks([])
ax.set_aspect("equal")
ax.set_title(f"PC{i+1} | Var: {var[i]*100:.2f}%", fontsize=14)
plt.subplots_adjust(hspace=0.05, wspace=0.05)
PLOTS_DIR.mkdir(parents=True, exist_ok=True)
out = PLOTS_DIR / "pod_modes.png"
plt.savefig(out, dpi=300, bbox_inches="tight")
print(f"Saved {out}")
plt.close()
if __name__ == "__main__":
main()