code: def add_arrows(self, cent, direction, mag=1, **kwargs):
          
          direction = direction.copy()
          if cent.ndim != 2:
              cent = cent.reshape((-1, 3))
  
          if direction.ndim != 2:
              direction = direction.reshape((-1, 3))
  
          direction[:,0] *= mag
          direction[:,1] *= mag
          direction[:,2] *= mag
  
          pdata = vtki.vector_poly_data(cent, direction)
          # Create arrow object
          arrow = vtk.vtkArrowSource()
          arrow.Update()
          glyph3D = vtk.vtkGlyph3D()
          glyph3D.SetSourceData(arrow.GetOutput())
          glyph3D.SetInputData(pdata)
          glyph3D.SetVectorModeToUseVector()
          glyph3D.Update()
  
          arrows = wrap(glyph3D.GetOutput())
  
          return self.add_mesh(arrows, **kwargs)
docs: Adds arrows to plotting object