Function: shah
SHAH  Discrete Shah-distribution
  Usage: f=shah(L,a);

  SHAH(L,a) computes the discrete, normalized Shah-distribution of
  length L with a distance of a between the spikes.

  The Shah distribution is defined by 

     f(n*a+1)=1/sqrt(L/a) 

  for integer n, otherwise f is zero.

  This is also known as an impulse train or as the comb function, because
  the shape of the function resembles a comb. It is the sum of unit
  impulses ('diracs') with the distance a.

  If a divides L, then the DFT of SHAH(L,a) is SHAH(L,L/a).

  The Shah function has an extremely bad time-frequency localization.
  It does not generate a Gabor frame for any L and a.

  Examples:
  ---------

  A simple spectrogram of the Shah function (includes the negative
  frequencies to display the whole TF-plane):

    sgram(shah(256,16),'dynrange',80,'nf')

Url: http://ltfat.github.io/doc/fourier/shah.html

Package: ltfat