import wave, struct, math, random

fe = 44100.0 # hertz
duree = 10.0       # secondes
freq = 110.0    # hertz
dt = 0.04
x, y = 0.0,0.0
m = 5.0


wavef = wave.open('vanderpol2.wav','w')
wavef.setnchannels(1) # mono
wavef.setsampwidth(2) #2 octets par piste
wavef.setframerate(fe)

for i in range(int(duree * fe)):
	m = 0.5-abs(i-duree*fe/2.0)/duree/fe
	m *= 10.0
	x += random.random()/32000.0
	y += 0.02*math.cos(freq*math.pi*float(i)/float(fe))
	x,y = x+dt*y, y+dt*(-x+m*(1-x**2)*y)
	value = int(2000*x)
	data = struct.pack('<h', value)
	wavef.writeframesraw( data )

wavef.writeframes('')
wavef.close()