Matrix square root.
S = SQRTM(A) is the matrix square root of A.
Complex results are produced if A has negative eigenvalues.
A warning message is printed if the computed S*S is not close to A.
[S,esterr] = sqrtm(A) does not print any warning message, but
returns an estimate of the relative residual, norm(S*S-A)/norm(A).
If A is real, symmetric and positive definite, or complex, Hermitian
and positive definite, then so is the computed matrix square root.
Some matrices, like A = [0 1; 0 0], do not have any square roots,
real or complex, and SQRTM cannot be expected to produce one.
See also EXPM1871LU2, LOGM , FUNM .