add a function to compute vn_SP(\eta)
add a function to compute vn_SP(\eta)

chunshen1987/HBTcorrelation_MCafterburner,chunshen1987/hadronic_afterburner_toolkit,chunshen1987/hadronic_afterburner_toolkit,chunshen1987/HBTcorrelation_MCafterburner,chunshen1987/HBTcorrelation_MCafterburner,chunshen1987/hadronic_afterburner_toolkit,chunshen1987/hadronic_afterburner_toolkit