ColdPlate-CFD-2000sims / 3_SourceCode /04_pod_variance.py
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"""
04 — Cumulative POD variance explained vs number of modes.
Fits PCA up to min(n_samples, n_points) modes on the full dataset and
plots the cumulative explained variance curve.
"""
import numpy as np
import matplotlib.pyplot as plt
from sklearn.decomposition import PCA
from _utils import load_data, PLOTS_DIR
def main():
_, fields, _, _ = load_data()
max_modes = min(fields.shape[0], fields.shape[1])
pca = PCA(n_components=max_modes).fit(fields)
cumulative = np.cumsum(pca.explained_variance_ratio_)
print(f"{'Modes':>6} {'Cum Var (%)':>12}")
for i in range(min(20, len(cumulative))):
print(f"{i+1:>6} {cumulative[i]*100:>12.4f}")
modes = np.arange(1, len(cumulative) + 1)
FS = 20
fig, ax = plt.subplots(figsize=(9, 9))
ax.plot(modes, cumulative * 100, "o-", color="tab:green",
linewidth=2, markersize=6)
ax.set_xlabel(r"Number of POD Modes, $r$", fontsize=FS)
ax.set_ylabel(r"Cumulative Variance Explained, $\eta_r$ (%)", fontsize=FS)
ax.tick_params(labelsize=FS - 4)
ax.set_ylim(None, 101)
ax.grid(True, alpha=0.3)
idx_9999 = np.searchsorted(cumulative, 0.9999) + 1
ax.set_xlim(0, min(idx_9999 + 5, len(cumulative)))
plt.tight_layout()
PLOTS_DIR.mkdir(parents=True, exist_ok=True)
out = PLOTS_DIR / "pod_mode_variance.png"
plt.savefig(out, dpi=300, bbox_inches="tight")
print(f"Saved {out}")
plt.close()
if __name__ == "__main__":
main()