#!/usr/bin/env python

import numpy
import matplotlib.pyplot as plt

n = 100
phase = numpy.pi/2.

data = []
for f in [0.5, 0.49, 0.25, 0.01]:
    tmp = []
    for i in range(n):
        tmp.append(numpy.cos(i * f * 2*numpy.pi + phase))
    data.append(tmp)

#plt.plot(data)

plt.subplot(221)
for d in data:
    plt.plot(d)

freqs = None

for d in data:
    if freqs is None:
        freqs = []
        for i in range(n/2 +1):
            freqs.append(i*1./n)

    tmp = numpy.fft.rfft(d)

    plt.subplot(212)
    plt.plot(freqs,abs(tmp)*2/n)
    plt.subplot(222)
    plt.plot(freqs,numpy.angle(tmp))

plt.show()