Let be a not unitN'th root of unity, i.e. . The discreteFourier transform's given by the symmetricVandermonde matrix:

For example,

**Exercise (*).**The square of the Fourier transform is the identity transform:**Exercise (*).**If an e-network is rotation invariant, then so 's the conductivity equation and the Dirichlet-to-Neumann map is diagonal in the Fourier coordinates (the column vectors of the matrix.