The graph Laplacian L = D − A encodes connectivity through its eigenvalues. The second smallest eigenvalue λ₂ (Fiedler value) measures graph connectivity. Its eigenvector (Fiedler vector) partitions the graph into communities. Colors show eigenvector components.
Fiedler value λ₂ ≈ ? — measures algebraic connectivity (larger = more connected). Fiedler vector partitions the graph: positive vs negative values suggest a natural cut.