Dear Author, I am trying to reproduce the 2.7 section of Tkwant tutorial: Green Function. When i try to calculate the lesser and retard greens's function occurred this error: green_lesser = [] green_retard = [] for time in times: green.evolve(time, 0) green.refine_intervals() green_lesser.append(green.lesser(site_0, site_0)) green_retard.append(green.retarded(site_0, site_0)) /home/gabriel/.local/lib/python3.9/site-packages/kwantspectrum/kwant_spectrum.py:361: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray. pvec = np.array([b * b / 3, 0, a * a]) --------------------------------------------------------------------------- ImportError Traceback (most recent call last) /tmp/ipykernel_158862/3957660185.py in <module> 7 green.refine_intervals() 8 ----> 9 green_lesser.append(green.lesser(site_0, site_0)) 10 green_retard.append(green.retarded(site_0, site_0)) ~/.local/lib/python3.9/site-packages/tkwant/greenfunctions.py in lesser(self, i, j, root) 375 def lesser(self, i, j, root=0): 376 if self._green_lesser is None: --> 377 self._init_lesser() 378 self._do_jobs(self._jobs_lesser) 379 return self._green_lesser.evaluate(i, j, root) ~/.local/lib/python3.9/site-packages/tkwant/greenfunctions.py in _init_lesser(self) 430 def _init_lesser(self): 431 logger.debug('init G^<') --> 432 self._green_lesser = _GreenGeneric(*self._args, **self._kwargs) 433 434 def _init_retarded(self): ~/.local/lib/python3.9/site-packages/tkwant/greenfunctions.py in __init__(self, refine, *args, **kwargs) 36 37 # no refine on individual wave function based on density ---> 38 self._state0 = manybody.State(*args, **kwargs, refine=False) 39 self._state1 = manybody.State(*args, **kwargs, refine=False) 40 ~/.local/lib/python3.9/site-packages/tkwant/manybody.py in __init__(self, syst, tmax, occupations, params, spectra, boundaries, intervals, refine, combine, error_op, scattering_state_type, manybody_wavefunction_type, mpi_distribute, comm) 1511 tasks.update(tasks_) 1512 -> 1513 self.comm = mpi.get_communicator(comm) 1514 1515 psi_init = self._calc_initial_state(tasks, self.comm) ~/.local/lib/python3.9/site-packages/tkwant/mpi.py in get_communicator(comm) 66 if comm is None: 67 if _COMM is None: ---> 68 communicator_init() 69 comm = _COMM 70 return comm ~/.local/lib/python3.9/site-packages/tkwant/mpi.py in communicator_init(comm) 48 if _COMM is None: 49 if comm is None: ---> 50 from mpi4py import MPI 51 _COMM = MPI.COMM_WORLD.Dup() 52 else: ImportError: libmpi.so.12: cannot open shared object file: No such file or directory Someone knows what should i do? I am beginner in python and kwant.