A procedure for checking the real part of Z(jw) for nonnegativeness

Checking Z(jw) for nonnegativeness reduces to an investigation of the behavior of the real part of the product of the pertinent V(jw) and the complex conjugate of I(jw). This real part function is constructed on the basis of piece-wise linearization of the voltage and current graphs and then reduced, using Tschebyscheff polynomials, to an equivalent ordinary polynomial which is tested for nonnegativeness by the usual methods between the values of plus and minus 1 of the polynomial variable