text: A 2D synchronous spectrum expresses the similarity between spectral of the data in the original dataset. In generalized 2D correlation spectroscopy this is mathematically expressed as covariance (or correlation).
  where:
  *Φ is the 2D synchronous spectrum
  *ν and ν are two spectral channels
  *y is the vector composed of the signal intensities in E in column ν
  *n the number of signals in the original dataset