1. School of Mathematics and Statistics, Northwestern Polytechnical University, Xi'an 710129, China
2. NPU-UoG International Cooperative Lab for Computation and Application in Cardiology, Xi'an 710129, China
3. Xi'an Key Laboratory of Scientific Computation and Applied Statistics, Xi'an 710129, China
4. Department of Mathematics, University of Cambridge, Cambridge CB2 1TN, UK
5. School of Mathematics and Statistics, University of Glasgow, Glasgow G12 8QQ, UK