NORMEST Estimate the matrix 2-norm.
 
    normest(S) is an estimate of the 2-norm of the matrix S.
 
    normest(S,tol) uses relative error tol instead of 1e-6.
 
    [nrm,cnt] = normest(..) also gives the number of iterations used.
 
    This function is a minor adaptation of Matlab's built-in NORMEST.