fft {<xray-fft-statement>} end

<xray-fft-statement> :==

  gridsize=<real>
  --{Gridsize for transform will be gridsize * high-resolution
     Default=0.333333}
  xgridfactor=<integer>
  --{Required factor for grid along x. Default=1}
  ygridfactor=<integer>
  --{Required factor for grid along y. Default=1}
  zgridfactor=<integer>
  --{Required factor for grid along z. Default=1}
  bscalefactor=<real>
  --{Temperature factor (in A^2) scale to decrease aliasing effects.
     Default=20}
  elimit=<real>
  --{Ratio of atomic form factor at maximum and at rcut in 
     e-logarithmic units. Default=7}
  memory=<integer>
  --{Space allocation for fft matrix the default is 500000 but if
     automemory is enabled the default becomes 2000000.}
  automemory=<logical>
  --{If true memory allocation space for fft is determined automatically.
     If false the allocation defined by memory is used.}
  prime=<integer>
  --{Maximum prime to be used in fft factorization.
     The default is machine-dependent.}
  base=<integer>
  --{Minimum prime to be used in fft factorization.
     Default is machine-dependent.}
  avoid=<integer>
  --{Avoid this factor in physical dimension of 3-d matrix 
     due to data bank conflicts on some shared memory machines.
     Default is machine-dependent.}