“…In recent years, numerical methods for Steklov eigenvalue problems have attracted more and more scholars' attention (see, e.g., [3,4,5,6,9,13,21,26,27,28,31,36,40]). It is well known that in the numerical approximation of partial differential equations, the adaptive procedures based on a posteriori error estimates, due to the less computational cost and time, are the mainstream direction and have gained an enormous importance.…”