Original sentence: It can be shown that the envelope  is governed by the PDE.The slowly varying envelope (SVE) of the electric field of a wave with central wave vector  and central frequency  of the pulse, is given by:.where the coefficients contains diffraction and dispersion effects which have been determined analytically with computer algebra and verified numerically to within third order for both isotropic and non-istropic media, valid in the near-field and far-field