code: def elekta_icon_fbp(ray_transform,
                      padding=False, filter_type='Hann', frequency_scaling=0.6,
                      parker_weighting=True):
      
      fbp_op = odl.tomo.fbp_op(ray_transform,
                               padding=padding,
                               filter_type=filter_type,
                               frequency_scaling=frequency_scaling)
      if parker_weighting:
          parker_weighting = odl.tomo.parker_weighting(ray_transform)
          fbp_op = fbp_op * parker_weighting
  
      return fbp_op
docs: Approximation of the FDK reconstruction used in the Elekta Icon.
  
      Parameters
      ----------
      ray_transform : `RayTransform`
          The ray transform to be used, should have an Elekta Icon geometry.
      padding : bool, optional
          Whether the FBP filter should use padding, increases memory use
          significantly.
      filter_type : str, optional
          Type of filter to apply in the FBP filter.
      frequency_scaling : float, optional
          Frequency scaling for FBP filter.
      parker_weighting : bool, optional
          Whether Parker weighting should be applied to compensate for partial
          scan.
  
      Returns
      -------
      elekta_icon_fbp : `DiscreteLp`
  
      Examples
      --------
      Create default FBP for default geometry:
  
      >>> from odl.contrib import tomo
      >>> geometry = tomo.elekta_icon_geometry()
      >>> space = tomo.elekta_icon_space()
      >>> ray_transform = odl.tomo.RayTransform(space, geometry)
      >>> fbp_op = tomo.elekta_icon_fbp(ray_transform)