Abstract
We consider the regular Sturm–Liouville problem
ACKNOWLEDGMENTS
The author would like to thank the referees for their careful reading and valuable comments in improving the original manuscript.
This work was supported by a Grant-in-Aid for Star of Purple and Gold from Nanjing University of Science and Technology (AB 41366) and a Grant-in-Aid for Scientific Research from Nanjing University of Science and Technology (XKF09041).