A SIMPLIFIED TWO-NODE COARSE-MESH FINITE DIFFERENCE METHOD FOR PIN-WISE CALCULATION WITH SP3 Wenbo Zhao, Yingrui Yu, Xiaoming Chai, Zhonghao Ning, Bin Zhang, Yun Cai, Kun Liu, Xingjie Peng and Junchong Yu EPJ Web Conf., 247 (2021) 02023 Published online: 22 February 2021 DOI: 10.1051/epjconf/202124702023