通讯录管理与应用，方便学生学习与应用，是一个很好的文件。-Chinese authors are preparing to petition Premier Wen Jiabao to help defend their copyrights that were allegedly infringed by Internet search giant Baidu

计算(多只)股票的期望值，收益率和协防差矩阵。-Calculate the expected stock yield and defend poor matrix.