  The nature of spin-glass phase of the four-dimensional Edwards-Anderson Ising
model is numerically studied by eigenmode analysis of the susceptibility matrix
up to the lattice size 10^4. Unlike the preceding results on smaller lattices,
our result suggests that there exist multiple extensive eigenvalues of the
matrix, which does not contradict replica-symmetry-breaking scenarios. The
sensitivity of the eigenmodes with respect to a temperature change is examined
using finite-size-scaling analysis and an evidence of anomalous sensitivity is
found. A computational advantage of dual formulation of the eigenmode analysis
in the study of large lattices is also discussed.
