relationship between active risk and active share
1、if the factor exposure is fully neutralized ,the active risk will be attributed to active share.
2、The active risk attributed to active share will be smaller if the number of securities is large and average idiosyncratic risk is small.
老师在讲解的时候说，这两种情形都是分散化，为什么一个是active share大（为什么neutralized就归因于weight），一个就是小呢？
average idiosyncratic risk is small为什么就是weight像？
