code: def norm_nuclear(X):
      r
  
      return np.sum(np.linalg.svd(sl.promote16(X), compute_uv=False))
docs: r"""Compute the nuclear norm
  
      .. math::
        \| X \|_* = \sum_i \sigma_i
  
      where :math:`\sigma_i` are the singular values of matrix :math:`X`.
  
  
      Parameters
      ----------
      X : array_like
        Input array :math:`X`
  
      Returns
      -------
      nncl : float
        Nuclear norm of `X`