for 然后下面跟sqrtm不可以吗？

A =rand(4)+eye(4);  % make sure Positive Def. Matrix
B = expm(0.1*logm(A));
norm(B*B*B*B*B*B*B*B*B*B-A)  % check precision

感谢回复的各位，matlab太强大了。
转移矩阵，竟然可以直接求N次方。
A=B^(1/n)

^   Matrix power.
    Z = X^y is X to the y power if y is a scalar and X is square. If y is an
    integer greater than one, the power is computed by repeated
    multiplication. For other values of y the calculation
    involves eigenvalues and eigenvectors.
    Z = x^Y is x to the Y power, if Y is a square matrix and x is a scalar,
    computed using eigenvalues and eigenvectors.
    Z = X^Y, where both X and Y are matrices, is an error.
  
    C = MPOWER(A,B) is called for the syntax 'A ^ B' when A or B is an
    object.