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def example_DMRG_SSH_infinite_S_xi_scaling():
	L = 50 # or whatever you like...
	t1, t2 = 0.5, 1.5
	t_array = np.array([(t1 if i % 2 == 0 else t2) for i in range(L-1)])
	model_params = {
    'L': L,
    't': t_array,
    'V': 0., 'mu': 0.,  # just free fermions, but you can generalize...
    'conserve': 'best'
	}
	M = FermionChain(model_params)
	product_state = ["up"] * int(M.lat.N_sites/2)+["down"]*(M.lat.N_sites-int(M.lat.N_sites/2))
	psi = MPS.from_product_state(M.lat.mps_sites(), product_state, bc=M.lat.bc_MPS)
	dmrg_params = {
        'start_env': 10,
        'mixer': None,
        #  'mixer_params': {'amplitude': 1.e-3, 'decay': 5., 'disable_after': 50},
        'trunc_params': {
            'chi_max': 50,
            #Dimension of the system
            'svd_min': 1.e-10
        },
        'update_env': 20,
        'start_env': 20,
        'max_E_err': 1.e-9,
        'max_S_err': 1.e-6,
        'update_env': 0,
    }

    #chi_list = np.arange(7, 31, 2)
	s_list = []
	xi_list = []
	eng = dmrg.TwoSiteDMRGEngine(psi, M, dmrg_params)
 # necessary if you for example have a fixed numer of sweeps, if you don't set this you option your simulation stops after initial number of sweeps!
        ##   DMRG Calculation    ##
	print("Start IDMRG CALCULATION")
	result=eng.run()
	eng.options['mixer'] = None
	psi.canonical_form()
	Sx=[]
	Sm=psi.expectation_value("Sm")
	Sp=psi.expectation_value("Sp")
	Sz=psi.expectation_value("Sz")
	for (item1, item2) in zip(Sm, Sp):
		Sx.append(item1+item2)

        ##   Calculating bond entropy and correlation length  ##
	s_list=psi.entanglement_entropy()
        # the bond 0 is between MPS unit cells and hence sensible even for 2D lattices.
        #xi_list.append(psi.correlation_length())
        #print(result)
	E_list.append(result[0])

	print(
          #np.mean(psi.expectation_value(M.H_bond)),
          s_list[-1],
          E_list[-1],
          #xi_list[-1],
          flush=True)
	tenpy.tools.optimization.optimize(3)  # quite some speedup for small chi

	print("SETTING NEW BOND DIMENSION")

	return s_list, xi_list, E_list,Sz

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	product_state = ["full", "empty"] * int(M.lat.N_sites/2)