Frequency-swept cosine generator.
| Parameters: | t : ndarray 
 f0 : float or ndarray, optional 
 t1 : float, optional 
 f1 : float, optional 
 method : {‘linear’, ‘quadratic’, ‘logarithmic’}, optional 
 phi : float 
 qshape : {‘convex’, ‘concave’} 
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Notes
If f0 is an array, it forms the coefficients of a polynomial in t (see numpy.polval). The polynomial determines the waveform frequency change in time. In this case, the values of f1, t1, method, and qshape are ignored.