Hello, I am ploting a fft periodogram of my data using a script (found in internet: http://linuxgazette.net/115/andreasen.html ) that gave me good results before. There should be a periodicity of >160 in the data as can be seen by eye. However, this script now says that there is periodicity of ~9. Can somebody explain me what's wrong? Thank you in advance. I present first the python script and second my data. ###### usage ############ python <script_name> <data_file> ######### PYTHON SCRIPT ########### from scipy import * import scipy.io.array_import from scipy import gplt from scipy import fftpack # Read file f=open(sys.argv[1], 'r') tempdata = scipy.io.array_import.read_array(f) minutes=tempdata[:,0] wolfer=tempdata[:,1] # plot data gplt.plot(minutes,wolfer,'title "Meas" with linespoints') gplt.xtitle('Minutes') gplt.ytitle('Wolfer number') gplt.grid("off") Y=fft(wolfer) n=len(Y) power = abs(Y[1:(n/2)])**2 nyquist=1./2 print nyquist freq=array(range(n/2))/(n/2.0)*nyquist period=1./freq # plot period gplt.plot(period[1:len(period)], power,'title "Simul" with linespoints') gplt.xaxis((50,400)) gplt.xtitle('Period [minutes]') gplt.ytitle('|FFT|**2') ########################## ######## DATA ############ 0 48 20 49 40 54 60 49 80 69 100 92 120 98 140 58 160 50 180 66 200 76 220 82 240 119 260 141 280 128 300 107 320 93 340 78 360 74 380 74 400 93 420 109 440 135 460 118 480 90 500 64 520 58 540 56 560 70 580 90 600 115 620 158 640 150 660 96 680 73 700 61 720 55 740 66 760 81 780 116 800 142 820 111 840 102 860 84 880 64 #################
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