code: def walnut_data():
      
      # TODO: Store data in some ODL controlled url
      url = 'http://www.fips.fi/dataset/CT_walnut_v1/FullSizeSinograms.mat'
      dct = get_data('walnut.mat', subset=DATA_SUBSET, url=url)
  
      # Change axes to match ODL definitions
      data = np.swapaxes(dct['sinogram1200'], 0, 1)[::-1, ::-1]
      data = data.astype('float')
  
      # Very crude gain normalization
      data = -np.log(data / np.max(data, axis=1)[:, None])
      return data
docs: Tomographic X-ray data of a walnut.
  
      Notes
      -----
      See the article `Tomographic X-ray data of a walnut`_ for further
      information.
  
      See Also
      --------
      walnut_geometry
  
      References
      ----------
      .. _Tomographic X-ray data of a walnut: https://arxiv.org/abs/1502.04064