PACIAE 2.1: An updated issue of the parton and hadron cascade model PACIAE 2.0 Original Research Article

We have updated the parton and hadron cascade model PACIAE 2.0 (cf. Ben-Hao Sa, Dai-Mei Zhou, Yu-Liang Yan, Xiao-Mei Li, Sheng-Qin Feng, Bao-Guo Dong, Xu Cai, Comput. Phys. Comm. 183 (2012) 333.) to the new issue of PACIAE 2.1. The PACIAE model is based on PYTHIA. In the PYTHIA model, once the hadron transverse momentum image is randomly sampled in the string fragmentation, the image and image components are originally put on the circle with radius image randomly. Now it is put on the circumference of ellipse with half major and minor axes of image and image, respectively, in order to better investigate the final state transverse momentum anisotropy.