Figure P7.54 shows the frequency response Ae(ejω) of a discrete-time FIR system for which the impulse response is
(a) Show thatAe(ejω) cannot correspond to an FIR filter generated by the Parks-McClellan algorithm with a passband edge frequency of π/3, a stopband edge frequency of 2π/3, and an error-weighting function of unity in the passband and stopband. Clearly explain your reasoning. Hint: The alternation theorem states that the best approximation is unique.
(b) Based on Figure P7.54 and the statement that Ae(ejω) cannot correspond to an optimal filter, what can be concluded about the value of L?