code: def test_cvxpy_1x21_to_6x6():
      """Test conversion from Voigt notation."""
      if have_cvxpy:
          V = np.arange(1, 22)[:, np.newaxis].astype(float)
          T = np.array(
              (
                  [
                      1,
                      4.24264069,
                      3.53553391,
                      4.94974747,
                      5.65685425,
                      6.36396103,
                  ],
                  [
                      4.24264069,
                      2,
                      2.82842712,
                      7.07106781,
                      7.77817459,
                      8.48528137,
                  ],
                  [
                      3.53553391,
                      2.82842712,
                      3,
                      9.19238816,
                      9.89949494,
                      10.60660172,
                  ],
                  [
                      4.94974747,
                      7.07106781,
                      9.19238816,
                      16,
                      13.43502884,
                      14.8492424,
                  ],
                  [
                      5.65685425,
                      7.77817459,
                      9.89949494,
                      13.43502884,
                      17,
                      14.14213562,
                  ],
                  [
                      6.36396103,
                      8.48528137,
                      10.60660172,
                      14.8492424,
                      14.14213562,
                      18,
                  ],
              )
          )
          npt.assert_array_almost_equal(
              qti.cvxpy_1x21_to_6x6(V).value, T
          )
          npt.assert_array_almost_equal(
              qti.cvxpy_1x21_to_6x6(qti.from_6x6_to_21x1(T)).value, T
          )
  
imports: import numpy
  import numpy.testing
  import dipy.reconst.qti
  from dipy.core.gradients import gradient_table
  from dipy.sims.voxel import vec2vec_rotmat
  from dipy.core.sphere import disperse_charges, HemiSphere
  from dipy.reconst.dti import fractional_anisotropy
  from dipy.testing.decorators import set_random_number_generator
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 6 for calling a global function with example usage: test_cvxpy_1x21_to_6x6() without return types