Subtract one Chebyshev series from another.
Returns the difference of two Chebyshev series c1  c2. The sequences of coefficients are from lowest order term to highest, i.e., [1,2,3] represents the series T_0 + 2*T_1 + 3*T_2.
Parameters :  c1, c2 : array_like


Returns :  out : ndarray

Notes
Unlike multiplication, division, etc., the difference of two Chebyshev series is a Chebyshev series (without having to “reproject” the result onto the basis set) so subtraction, just like that of “standard” polynomials, is simply “componentwise.”
Examples
>>> from numpy.polynomial import chebyshev as C
>>> c1 = (1,2,3)
>>> c2 = (3,2,1)
>>> C.chebsub(c1,c2)
array([2., 0., 2.])
>>> C.chebsub(c2,c1) # C.chebsub(c1,c2)
array([ 2., 0., 2.])