code: def cvxpy_1x6_to_3x3(V):
      """Convert a 1 x 6 vector into a symmetric 3 x 3 matrix.
  
      Parameters
      ----------
      V : numpy.ndarray
          An array of size (1, 6).
  
      Returns
      -------
      T : cvxpy.bmat
          Converted matrix of size (3, 3).
  
      Notes
      -----
      The conversion of a matrix into a vector is defined as
  
          .. math::
  
              \mathbf{V} = \begin{bmatrix}
              T_{11} & T_{22} & T_{33} &
              \sqrt{2} T_{23} & \sqrt{2} T_{13} & \sqrt{2} T_{12}
              \end{bmatrix}^T
      """
      if V.shape[0] == 6:
          V = V.T
  
      f = 1 / np.sqrt(2)
  
      T = cp.bmat(
          [
              [V[0, 0], f * V[0, 5], f * V[0, 4]],
              [f * V[0, 5], V[0, 1], f * V[0, 3]],
              [f * V[0, 4], f * V[0, 3], V[0, 2]],
          ]
      )
      return T
  
imports: from warnings import warn
  import numpy
  from dipy.reconst.base import ReconstModel
  from dipy.reconst.dti import auto_attr
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 5 for calling a global function with example usage: cvxpy_1x6_to_3x3(V) and returns: T