E. ŻOŁOPA and A. BRAŃSKI, “Comparison of Formulas Obtained for Analytical and LQ Idea Approaches to Determine the Optimal Actuator Location in Active Multimodal Beam Vibration Reduction”, Arch. Acoust., vol. 39, no. 4, pp. 599–603, Nov. 2014, doi: 10.2478/aoa-2014-0064.