The matrices come from Jifeng Zhao, Northwestern University. The stiffness and mass matrices arise from a extended finite element model to predict phononic band gap of a three-dimensional two-phase composite with periodic SCC crystal structure. In addition, periodic boundary conditions are applied on the primary unit cell by employing Bloch wave analysis.

Compute first 40 eigensolutions
K x = lamda M x
K and M are real and symmetric (Aug. 2014)
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petsc_stiff20.dat: 
  type: seqaij
  rows=1591812, cols=1591812, total: nonzeros=6.93869e+07
petsc_mass20.dat
  type: seqaij
  rows=1591812, cols=1591812, total: nonzeros=4.09661e+07,
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petsc_stiff33.dat:
  type: seqaij
  rows=1591812, cols=1591812, total: nonzeros=7.05468e+07,
petsc_mass33.dat:
  type: seqaij
  rows=1591812, cols=1591812, total: nonzeros=4.13649e+07