update norm estimation for more numerical stability
update norm estimation for more numerical stability

Signed-off-by: Sylvain Chevallier <d115dbaca926e1b13dac5ad9e4d7418855613cfa@uvsq.fr>

nkoep/pymanopt,nkoep/pymanopt,pymanopt/pymanopt,nkoep/pymanopt,pymanopt/pymanopt