code: def grid_to_elliptical_radii(self, grid):
          
          return np.sqrt(np.add(np.square(grid[:, 1]), np.square(np.divide(grid[:, 0], self.axis_ratio))))
docs: Convert a grid of (y,x) coordinates to an elliptical radius.
  
          If the coordinates have not been transformed to the profile's geometry, this is performed automatically.
  
          Parameters
          ----------
          grid : TransformedGrid(ndarray)
              The (y, x) coordinates in the reference frame of the elliptical profile.