Multiply one Chebyshev series by another.
Returns the product of two Chebyshev series c1 * c2. The arguments are sequences of coefficients, from lowest order “term” to highest, e.g., [1,2,3] represents the series T_0 + 2*T_1 + 3*T_2.
Parameters :  c1, c2 : array_like


Returns :  out : ndarray

Notes
In general, the (polynomial) product of two Cseries results in terms that are not in the Chebyshev polynomial basis set. Thus, to express the product as a Cseries, it is typically necessary to “reproject” the product onto said basis set, which typically produces “unintuitive live” (but correct) results; see Examples section below.
Examples
>>> from numpy.polynomial import chebyshev as C
>>> c1 = (1,2,3)
>>> c2 = (3,2,1)
>>> C.chebmul(c1,c2) # multiplication requires "reprojection"
array([ 6.5, 12. , 12. , 4. , 1.5])