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from matplotlib import *
use('Qt4Agg')
from matplotlib.pyplot import *
from numpy import *

def PlotRFFT(x, y):
    ### PlotRFFT(x, y): plots the FFT of y assuming y is real.  Generates one plot with two subfigures: abscissa = frequency and abscissa = period.

    f = fft.rfft(y)/len(y)*2
    nu = fft.rfftfreq(len(y), x[1]-x[0])
    p = 1/nu
    amp = abs(f)
        
    subplot(2,1,1)
    loglog(nu, amp)
    xlabel('Frequency')
    ylabel('Amplitude')
    subplot(2,1,2)
    loglog(p, amp)
    xlabel('Period')
    ylabel('Amplitude')
    show()

if __file__ == '__main__':
    x = arange(0,1000, 0.001)
    y = sin(2*pi*x/7)
    PlotRFFT(x, y)