human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge groups authors who co-authored the same paper.

Details of the hypergraph:
Center hyperedge (induced by source paper "A Push–Pull Class-E Inverter With Improved Efficiency"):
  Abstract: This paper presents a concept for improving the efficiency of a push-pull Class-E inverter. The concept consists of lowering the root-mean-square transistor current (in reducing the transistor power losses) only by adding a differential capacitor to a push-pull Class-E topology. Theoretical explanations and confirming experimental results are given.

Includes members:
  Member "High-Efficiency Class E, $hboxEF_2$ , and $hboxE/F_3$ Inverters":
    also connected through other hyperedges:
      (none)

Question: Please tell me which research area the co-authored paper (i.e., the source paper of the center hyperedge) belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Engineering