sqroot - W*W' hermitian factorization
returns W such that X=W*W' (uses SVD).
X=rand(5,2)*rand(2,5);X=X*X'; W=sqroot(X) norm(W*W'-X,1) // X=rand(5,2)+%i*rand(5,2);X=X*X'; W=sqroot(X) norm(W*W'-X,1)