!rm fft_x.ps
#set term postscript enhanced color
#set output 'fft_x.ps'
name='fft.dat'
n_fft=256
set multiplot
set origin 0.,0.
unset title
set size 1,0.5
unset logscale
set ytics
min=1+(n-1)*n_fft/2
set xlabel 'turn'
max=n_fft+(n-1)*n_fft/2
set xrange [min:max]
plot name u ($1+min-1):3 i n:n w l lc 1 t 'position'
set origin 0.,0.5
set title 'horizontal'
set logscale y
set ytics 1.e-8,1.e-2
set xlabel 'fractional tune'
set xrange[0.5:1.]
plot name u (1-$1/n_fft/2):($5**2) i n:n w l lc 2 t 'fft'