Frequencyswept cosine generator, with a timedependent frequency.
This function generates a sinusoidal function whose instantaneous frequency varies with time. The frequency at time t is given by the polynomial poly.
Parameters :  t : ndarray
poly : 1D arraylike or instance of numpy.poly1d
phi : float, optional


Returns :  sweep_poly : ndarray

See also
Notes
New in version 0.8.0.
If poly is a list or ndarray of length n, then the elements of poly are the coefficients of the polynomial, and the instantaneous frequency is:
f(t) = poly[0]*t**(n1) + poly[1]*t**(n2) + ... + poly[n1]
If poly is an instance of numpy.poly1d, then the instantaneous frequency is:
f(t) = poly(t)
Finally, the output s is:
cos(phase + (pi/180)*phi)
where phase is the integral from 0 to t of 2 * pi * f(t), f(t) as defined above.