“…The varying coefficient model (2) has been well studied via various estimation methods, see for example, Hastie and Tibshirani (
1993), Fan and Zhang (
1999); Li, Li, Lian, and Tong (
2017); Zhao and Lian (
2016), Yang, Li, and Peng (
2014), Li, Feng, and Peng (
2011), Li, Xue, and Lian (
2011); Zhang and Peng (
2010); Lv, Fan, Lian, Suzuki, and Fukumizu (
2020), Zhang, Zhou, Xu, and Li (
2018), Zhao, Peng, and Huang (
2018), Lian (
2015), Lian, Lai, and Liang (
2013), Fan and Huang (
2005). In this paper, we adopt the local linear regression technique (Fan & Huang,
2005) to estimate
in model (2) as an illustration.…”