def __init__(self, freq, tau, T, samplerate, t0=None, phi=0):
"""Initialize signal without any noise.
Arguments:
* freq is the frequency of the signal in hertz
* tau is the decay constant in seconds
* T is the length of the signal in seconds
* samplerate in Hz
* t0 is the time the signal starts
* dphi is the phase of the signal, 0 means cosine
"""
Waveform.__init__(self, T, samplerate)
self.samples = cos(2*pi*freq*self.time)*exp(-self.time/tau)
if t0:
self.samples = hstack((zeros(t0/selg.sampleinterval), self.samples))[:len(self.samples)]
