Demonstration programs for solving eigenvalue problems
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eigen_demo1:   Solution of the eigenvalue problem with a given symmetric matrix.
               All eigenvalues are computed

eigen_demo2:   Solution of the eigenvalue problem for the Laplace equation with homogeneous
               Dirichlet boundary conditions.
               Eigenvalues are computed, eigenvectors are stored in Gmsh files.
               To be used with input file: eigen_demo2 eigen_demo2.dat

