matlab - Algorithm to compute a real logarithm of a real matrix? -

i algorithm find real logarithm of real matrix.

the existence theorem found here is:

a real matrix has real logarithm if , if invertible , each jordan block belonging negative eigenvalue occurs number of times.

i working in matlab adaptable algorithm do. example matrix in following satisfies both conditions.

a = [-1 1 0 0; 0 -1 0 0; 0 0 -1 1; 0 0 0 -1]; realmatrixlogarithm?(a) = x; 

edit: have attempted understand algorithm given in this article, seems valid normal matrices.

thank help.