import random
def generate_noise_ravn(a,b, num_points, filename):
    signal=[random.uniform(a, b) for x in range(num_points)]
    with open(filename, 'w') as f:
        for i in range(0,num_points,3):
            line=", ".join(str(value) for value in signal[i:i+3])
            f.write(line+"\n")
    return signal