function d=digsev(ra,r)
  [m,n]=size(r);
  if ((size(ra,1)~=m) | (size(ra,2)~=n))
     error('dimensoes devem combinar')
  end
  if (norm(ra-r) < %eps) | (norm(r) < %eps)
     d = 16.0;
  else
     d = max(0,-log10( 2*norm(ra-r)/norm(r) ));
  end
endfunction
