Matrix logarithm.

  L = LOGM(A) is the matrix logarithm of A.

  Complex results are produced if A has negative eigenvalues.

  A warning message is printed if the computed expm(L) is not close to A.



  [L,esterr] = logm(A) does not print any warning message, but 

  returns an estimate of the relative residual, norm(expm(L)-A)/norm(A).



  If A is real symmetric or complex Hermitian, then so is LOGM(A).



  Some matrices, like A = [0 1; 0 0], do not have any logarithms,

  real or complex, and LOGM cannot be expected to produce one.



  See also EXPM1871LU2, SQRTM15RK9IN, FUNM193ZLU2.