fermi

  FERMI creates a 2D Fermi filter.
    FFILTER = FERMI(XDIM,CUTOFF,TRANS_WIDTH) calculates a 2D
      Fermi filter on a grid with dimensions XDIM * XDIM. 
     The cutoff frequency is defined by CUTOFF and represents
      the radius (in pixels) of the circular symmetric function   
      at which the amplitude drops below 0.5
     TRANS_WIDTH defines the width of the transition. 

     Author: Wally Block, UW-Madison  02/23/01. 

     Call: ffilter = fermi(xdim, cutoff, trans_width);