对称矩阵逆特征值问题的向后误差

给出了对称矩阵逆特征值问题的一个更一般的向后误差计算公式,推广了孙继广的结论,并给出一个简单的证明。     

Comment: Comments on "How to repair the Hill cipher"

A modification of the Hill cipher algorithm was recently proposed by Ismail et al.(2006), who claimed that their new scheme could offer more security than the original one due to an extra non-linearity layer introduced via an elaborated key generation mechanism. That mechanism produces one different encryption key for each one of the plaintext blocks. Nevertheless, we show in this paper that their method still has severe security flaws whose weaknesses are essentially the same as that already found in the original Hill cipher scheme.     

轴手性化合物立体构型的便捷判断法

在多年教学经验和对轴手性化合物构型判断方法研究的基础上,提出了一种易于教师讲授和学生理解掌握的轴手性化合物立体构型简便的标记方法。