A parallel-plate capacitor is fully charged and connected in series to an inductor only. The capacitor initially stores charge \(q\) and electric potential energy \(U^{E}\). Once the circuit is closed, charge carriers flow from the capacitor, producing a current in the circuit. When the charge on the capacitor has been reduced to \(q / 2\), what is the magnetic potential energy \(U^{B}\) stored in the inductor? Report your answer in terms of \(U^{E}\).