portfolio 1: total active risk 1=(true active risk 1^2 + misfit active risk 1^2)^(1/2) portfolio 2: total active risk 2=(truc active risk 2的平方+ misfit active risk 2的平方)开根号
total active risk=[75%^2x(total active risk 1)^2 + 25%^2x (total active risk 2)^2 + 2 x 75% x 25% x (total active risk 1 )x (total active risk 2 )x correlation(1,2)]^(1/2)