Returns difference from subtraction of two polynomials input as sequences.
Returns difference of polynomials; a1  a2. Input polynomials are represented as an array_like sequence of terms or a poly1d object.
Parameters:  a1 : {array_like, poly1d}
a2 : {array_like, poly1d}


Returns:  out : {ndarray, poly1d}

Examples
>>> np.polysub([2, 10, 2], [3, 10, 4])
array([1, 0, 2])