Exemple #1
0
def test_cf_G_tau_and_G_iw_nonint(verbose=False):

    beta = 3.22
    eps = 1.234

    niw = 64
    ntau = 2 * niw + 1
    
    H = eps * c_dag(0,0) * c(0,0)

    fundamental_operators = [c(0,0)]

    ed = TriqsExactDiagonalization(H, fundamental_operators, beta)

    # ------------------------------------------------------------------
    # -- Single-particle Green's functions

    G_tau = GfImTime(beta=beta, statistic='Fermion', n_points=ntau, target_shape=(1,1))
    G_iw = GfImFreq(beta=beta, statistic='Fermion', n_points=niw, target_shape=(1,1))

    G_iw << inverse( iOmega_n - eps )
    G_tau << InverseFourier(G_iw)

    G_tau_ed = GfImTime(beta=beta, statistic='Fermion', n_points=ntau, target_shape=(1,1))
    G_iw_ed = GfImFreq(beta=beta, statistic='Fermion', n_points=niw, target_shape=(1,1))

    ed.set_g2_tau(G_tau_ed[0, 0], c(0,0), c_dag(0,0))
    ed.set_g2_iwn(G_iw_ed[0, 0], c(0,0), c_dag(0,0))

    # ------------------------------------------------------------------
    # -- Compare gfs

    from pytriqs.utility.comparison_tests import assert_gfs_are_close
    
    assert_gfs_are_close(G_tau, G_tau_ed)
    assert_gfs_are_close(G_iw, G_iw_ed)
    
    # ------------------------------------------------------------------
    # -- Plotting
    
    if verbose:
        from pytriqs.plot.mpl_interface import oplot, plt
        subp = [3, 1, 1]
        plt.subplot(*subp); subp[-1] += 1
        oplot(G_tau.real)
        oplot(G_tau_ed.real)

        plt.subplot(*subp); subp[-1] += 1
        diff = G_tau - G_tau_ed
        oplot(diff.real)
        oplot(diff.imag)
        
        plt.subplot(*subp); subp[-1] += 1
        oplot(G_iw)
        oplot(G_iw_ed)
        
        plt.show()
Exemple #2
0
def make_calc(beta=2.0, h_field=0.0):
    
    # ------------------------------------------------------------------
    # -- Hubbard atom with two bath sites, Hamiltonian

    p = ParameterCollection(
        beta = beta,
        h_field = h_field,
        U = 5.0,
        ntau = 40,
        niw = 15,
        )

    p.mu = 0.5*p.U
    
    # ------------------------------------------------------------------

    print '--> Solving SIAM with parameters'
    print p
    
    # ------------------------------------------------------------------

    up, do = 'up', 'dn'
    docc = c_dag(up,0) * c(up,0) * c_dag(do,0) * c(do,0)
    mA = c_dag(up,0) * c(up,0) - c_dag(do,0) * c(do,0)
    nA = c_dag(up,0) * c(up,0) + c_dag(do,0) * c(do,0)

    p.H = -p.mu * nA + p.U * docc + p.h_field * mA
    
    # ------------------------------------------------------------------

    fundamental_operators = [c(up,0), c(do,0)]
    
    ed = TriqsExactDiagonalization(p.H, fundamental_operators, p.beta)

    g_tau = GfImTime(beta=beta, statistic='Fermion', n_points=40, indices=[0])
    g_iw = GfImFreq(beta=beta, statistic='Fermion', n_points=10, indices=[0])

    p.G_tau = BlockGf(name_list=[up,do], block_list=[g_tau]*2, make_copies=True)
    p.G_iw = BlockGf(name_list=[up,do], block_list=[g_iw]*2, make_copies=True)
    
    ed.set_g2_tau(p.G_tau[up], c(up,0), c_dag(up,0))
    ed.set_g2_tau(p.G_tau[do], c(do,0), c_dag(do,0))

    ed.set_g2_iwn(p.G_iw[up], c(up,0), c_dag(up,0))
    ed.set_g2_iwn(p.G_iw[do], c(do,0), c_dag(do,0))

    p.magnetization = ed.get_expectation_value(0.5 * mA)
    p.magnetization2 = ed.get_expectation_value(0.25 * mA * mA)
    
    # ------------------------------------------------------------------
    # -- Store to hdf5
    
    filename = 'data_pyed_h_field_%4.4f.h5' % h_field
    with HDFArchive(filename,'w') as res:
        res['p'] = p
Exemple #3
0
    # -- Exact diagonalization

    fundamental_operators = [
        c(up, 0), c(do, 0),
        c(up, 1), c(do, 1),
        c(up, 2), c(do, 2)
    ]

    ed = TriqsExactDiagonalization(H, fundamental_operators, beta)

    # ------------------------------------------------------------------
    # -- Single-particle Green's functions

    g_tau = GfImTime(name=r'$g$',
                     beta=beta,
                     statistic='Fermion',
                     n_points=50,
                     indices=[1])

    g_iwn = GfImFreq(name='$g$',
                     beta=beta,
                     statistic='Fermion',
                     n_points=10,
                     indices=[1])

    ed.set_g2_tau(g_tau, c(up, 0), c_dag(up, 0))
    ed.set_g2_iwn(g_iwn, c(up, 0), c_dag(up, 0))

    # ------------------------------------------------------------------
    # -- Two particle Green's functions
Exemple #4
0
def make_calc(U=10):

    # ------------------------------------------------------------------
    # -- Hubbard atom with two bath sites, Hamiltonian

    params = dict(
        beta=2.0,
        V1=2.0,
        V2=5.0,
        epsilon1=0.00,
        epsilon2=4.00,
        mu=2.0,
        U=U,
        ntau=40,
        niw=15,
    )

    # ------------------------------------------------------------------

    class Dummy():
        def __init__(self):
            pass

    d = Dummy()  # storage space
    d.params = params

    print '--> Solving SIAM with parameters'
    for key, value in params.items():
        print '%10s = %-10s' % (key, str(value))
        globals()[key] = value  # populate global namespace

    # ------------------------------------------------------------------

    up, do = 0, 1
    docc = c_dag(up, 0) * c(up, 0) * c_dag(do, 0) * c(do, 0)
    nA = c_dag(up, 0) * c(up, 0) + c_dag(do, 0) * c(do, 0)
    nB = c_dag(up, 1) * c(up, 1) + c_dag(do, 1) * c(do, 1)
    nC = c_dag(up, 2) * c(up, 2) + c_dag(do, 2) * c(do, 2)

    d.H = -mu * nA + epsilon1 * nB + epsilon2 * nC + U * docc + \
        V1 * (c_dag(up,0)*c(up,1) + c_dag(up,1)*c(up,0) + \
              c_dag(do,0)*c(do,1) + c_dag(do,1)*c(do,0) ) + \
        V2 * (c_dag(up,0)*c(up,2) + c_dag(up,2)*c(up,0) + \
              c_dag(do,0)*c(do,2) + c_dag(do,2)*c(do,0) )

    # ------------------------------------------------------------------
    # -- Exact diagonalization

    fundamental_operators = [
        c(up, 0), c(do, 0),
        c(up, 1), c(do, 1),
        c(up, 2), c(do, 2)
    ]

    ed = TriqsExactDiagonalization(d.H, fundamental_operators, beta)

    # ------------------------------------------------------------------
    # -- Single-particle Green's functions

    Gopt = dict(beta=beta, statistic='Fermion', indices=[1])
    d.G_tau = GfImTime(name=r'$G(\tau)$', n_points=ntau, **Gopt)
    d.G_iw = GfImFreq(name='$G(i\omega_n)$', n_points=niw, **Gopt)

    ed.set_g2_tau(d.G_tau, c(up, 0), c_dag(up, 0))
    ed.set_g2_iwn(d.G_iw, c(up, 0), c_dag(up, 0))

    # chi2pp = + < c^+_u(\tau^+) c_u(0^+) c^+_d(\tau) c_d(0) >
    #        = - < c^+_u(\tau^+) c^+_d(\tau) c_u(0^+) c_d(0) >

    chi2opt = dict(beta=beta, statistic='Fermion', indices=[1], n_points=ntau)
    d.chi2pp_tau = GfImTime(name=r'$\chi^{(2)}_{PP}(\tau)$', **chi2opt)
    ed.set_g2_tau(d.chi2pp_tau,
                  c_dag(up, 0) * c_dag(do, 0),
                  c(up, 0) * c(do, 0))
    d.chi2pp_tau *= -1.0 * -1.0  # commutation sign and gf sign
    d.chi2pp_iw = g_iw_from_tau(d.chi2pp_tau, niw)

    # chi2ph = < c^+_u(\tau^+) c_u(\tau) c^+_d(0^+) c_d(0) >

    d.chi2ph_tau = GfImTime(name=r'$\chi^{(2)}_{PH}(\tau)$', **chi2opt)
    #d.chi2ph_tau = Gf(name=r'$\chi^{(2)}_{PH}(\tau)$', **chi2opt)
    ed.set_g2_tau(d.chi2ph_tau,
                  c_dag(up, 0) * c(up, 0),
                  c_dag(do, 0) * c(do, 0))
    d.chi2ph_tau *= -1.0  # gf sign
    d.chi2ph_iw = g_iw_from_tau(d.chi2ph_tau, niw)

    # ------------------------------------------------------------------
    # -- Two particle Green's functions

    imtime = MeshImTime(beta, 'Fermion', ntau)
    prodmesh = MeshProduct(imtime, imtime, imtime)
    G2opt = dict(mesh=prodmesh, target_shape=[1, 1, 1, 1])

    d.G02_tau = Gf(name='$G^{(2)}_0(\tau_1, \tau_2, \tau_3)$', **G2opt)
    ed.set_g40_tau(d.G02_tau, d.G_tau)
    d.G02_iw = chi4_iw_from_tau(d.G02_tau, niw)

    d.G2_tau = Gf(name='$G^{(2)}(\tau_1, \tau_2, \tau_3)$', **G2opt)
    ed.set_g4_tau(d.G2_tau, c_dag(up, 0), c(up, 0), c_dag(do, 0), c(do, 0))
    #ed.set_g4_tau(d.G2_tau, c(up,0), c_dag(up,0), c(do,0), c_dag(do,0)) # <cc^+cc^+>
    d.G2_iw = chi4_iw_from_tau(d.G2_tau, niw)

    # -- trying to fix the bug in the fft for w2

    d.G02_iw.data[:] = d.G02_iw.data[:, ::-1, ...].conj()
    d.G2_iw.data[:] = d.G2_iw.data[:, ::-1, ...].conj()

    # ------------------------------------------------------------------
    # -- 3/2-particle Green's functions (equal times)

    prodmesh = MeshProduct(imtime, imtime)
    chi3opt = dict(mesh=prodmesh, target_shape=[1, 1, 1, 1])

    # chi3pp = <c^+_u(\tau) c_u(0^+) c^+_d(\tau') c_d(0) >
    #        = - <c^+_u(\tau) c^+_d(\tau') c_u(0^+) c_d(0) >

    d.chi3pp_tau = Gf(name='$\Chi^{(3)}_{PP}(\tau_1, \tau_2, \tau_3)$',
                      **chi3opt)
    ed.set_g3_tau(d.chi3pp_tau, c_dag(up, 0), c_dag(do, 0),
                  c(up, 0) * c(do, 0))
    d.chi3pp_tau *= -1.0  # from commutation
    d.chi3pp_iw = chi3_iw_from_tau(d.chi3pp_tau, niw)

    # chi3ph = <c^+_u(\tau) c_u(\tau') c^+_d(0^+) c_d(0) >

    d.chi3ph_tau = Gf(name='$\Chi^{(3)}_{PH}(\tau_1, \tau_2, \tau_3)$',
                      **chi3opt)
    ed.set_g3_tau(d.chi3ph_tau, c_dag(up, 0), c(up, 0),
                  c_dag(do, 0) * c(do, 0))
    d.chi3ph_iw = chi3_iw_from_tau(d.chi3ph_tau, niw)

    # ------------------------------------------------------------------
    # -- Store to hdf5

    filename = 'data_ed.h5'
    with HDFArchive(filename, 'w') as res:
        for key, value in d.__dict__.items():
            res[key] = value
Exemple #5
0
   print g(tau.real)

2. Linear interpolation for higher order tau greens function

g4_tau(t1, t2, t3)

"""

import itertools
import numpy as np
from pytriqs.gf import Gf, GfImTime, MeshImTime, MeshProduct

ntau = 10
beta = 1.2345

g_tau = GfImTime(name='g_tau', beta=beta, statistic='Fermion', n_points=ntau, indices=[1])

tau = np.array([tau.value for tau in g_tau.mesh])
g_ref = np.exp(-beta * tau)
g_tau.data[:, 0, 0] = np.exp(-beta * tau)

for tau in g_tau.mesh:
    g_tau[tau] = np.exp(-beta * tau)

for idx, tau in enumerate(g_tau.mesh):

    # comparison does not work at beta since the evaluation g_tau() wraps..
    if idx == len(g_tau.mesh)-1: break
    
    #diff_interp = g_tau(tau)[0,0] - g_ref[idx] # FIXME: tau is complex
    
Exemple #6
0
2. Linear interpolation for higher order tau greens function

g4_tau(t1, t2, t3)

"""

import itertools
import numpy as np
from pytriqs.gf import Gf, GfImTime, MeshImTime, MeshProduct

ntau = 10
beta = 1.2345

g_tau = GfImTime(name='g_tau',
                 beta=beta,
                 statistic='Fermion',
                 n_points=ntau,
                 indices=[1])

tau = np.array([tau.value for tau in g_tau.mesh])
g_ref = np.exp(-beta * tau)
g_tau.data[:, 0, 0] = np.exp(-beta * tau)

for tau in g_tau.mesh:
    g_tau[tau] = np.exp(-beta * tau)

for idx, tau in enumerate(g_tau.mesh):

    # comparison does not work at beta since the evaluation g_tau() wraps..
    if idx == len(g_tau.mesh) - 1: break
Exemple #7
0
# ----------------------------------------------------------------------
if __name__ == '__main__':

    if mpi.is_master_node():
        with HDFArchive('data_model.h5','r') as A: m = A["p"]
        with HDFArchive('data_pyed.h5','r') as A: p = A["p"]
    else:
        m, p = None, None
    m, p = mpi.bcast(m), mpi.bcast(p)

    p.chi_field = np.zeros((4, 4, 4, 4), dtype=np.complex)
    p.g_tau_field = {}

    g_tau = GfImTime(name=r'$g$', beta=m.beta,
                     statistic='Fermion', n_points=50,
                     target_shape=(4, 4))

    # -- The field is symmetric in (i1, i2)
    # -- only calculate upper triangle
    
    index_list = []
    for i1 in xrange(4):
        for i2 in xrange(i1, 4):
            index_list.append((i1, i2))

    #F = 0.0001 / m.beta
    F = 0.1 / m.beta
    F_vec = np.array([-F, F])
    
    work_list = np.array(index_list)
Exemple #8
0
    # -- Weiss field of the bath

    h_tot = quadratic_matrix_from_operator(p.H_bath + p.H_loc, p.op_full)

    g0_iw = GfImFreq(beta=p.beta,
                     statistic='Fermion',
                     n_points=p.nw,
                     target_shape=(8, 8))

    g0_iw << inverse(iOmega_n - h_tot)

    p.g0_iw = g0_iw[:4, :4]  # -- Cut out impurity Gf
    p.g0t_iw = g2_single_particle_transform(p.g0_iw, p.T.H)

    p.g0_tau = GfImTime(beta=p.beta,
                        statistic='Fermion',
                        n_points=p.ntau,
                        target_shape=(4, 4))

    p.g0_tau << InverseFourier(p.g0_iw)
    p.g0t_tau = g2_single_particle_transform(p.g0_tau, p.T.H)

    p.g0_tau_ref = g2_single_particle_transform(p.g0t_tau, p.T)
    np.testing.assert_array_almost_equal(p.g0_tau_ref.data, p.g0_tau.data)

    # -- Interaction Hamiltonian: Kanamori interaction

    U_ab, UPrime_ab = U_matrix_kanamori(n_orb=p.num_orbitals,
                                        U_int=p.U,
                                        J_hund=p.J)

    H_int = h_int_kanamori(p.spin_names,
Exemple #9
0
def test_two_particle_greens_function():

    # ------------------------------------------------------------------
    # -- Hubbard atom with two bath sites, Hamiltonian
    
    beta = 2.0
    V1 = 2.0
    V2 = 5.0
    epsilon1 = 0.00
    epsilon2 = 4.00
    mu = 2.0
    U = 0.0

    up, do = 0, 1
    docc = c_dag(up,0) * c(up,0) * c_dag(do,0) * c(do,0)
    nA = c_dag(up,0) * c(up,0) + c_dag(do,0) * c(do,0)
    nB = c_dag(up,1) * c(up,1) + c_dag(do,1) * c(do,1)
    nC = c_dag(up,2) * c(up,2) + c_dag(do,2) * c(do,2)

    H = -mu * nA + epsilon1 * nB + epsilon2 * nC + U * docc + \
        V1 * (c_dag(up,0)*c(up,1) + c_dag(up,1)*c(up,0) + \
              c_dag(do,0)*c(do,1) + c_dag(do,1)*c(do,0) ) + \
        V2 * (c_dag(up,0)*c(up,2) + c_dag(up,2)*c(up,0) + \
              c_dag(do,0)*c(do,2) + c_dag(do,2)*c(do,0) )
    
    # ------------------------------------------------------------------
    # -- Exact diagonalization

    fundamental_operators = [
        c(up,0), c(do,0), c(up,1), c(do,1), c(up,2), c(do,2)]
    
    ed = TriqsExactDiagonalization(H, fundamental_operators, beta)

    # ------------------------------------------------------------------
    # -- single particle Green's functions

    g_tau = GfImTime(name=r'$g$', beta=beta,
                     statistic='Fermion', n_points=100,
                     target_shape=(1,1))
    
    ed.set_g2_tau(g_tau[0, 0], c(up,0), c_dag(up,0))
    
    # ------------------------------------------------------------------
    # -- Two particle Green's functions

    ntau = 10
    imtime = MeshImTime(beta, 'Fermion', ntau)
    prodmesh = MeshProduct(imtime, imtime, imtime)

    g40_tau = Gf(name='g40_tau', mesh=prodmesh, target_shape=(1,1,1,1))
    g4_tau = Gf(name='g4_tau', mesh=prodmesh, target_shape=(1,1,1,1))

    ed.set_g40_tau_matrix(g40_tau, g_tau)
    ed.set_g4_tau(g4_tau[0, 0, 0, 0], c(up,0), c_dag(up,0), c(up,0), c_dag(up,0))

    # ------------------------------------------------------------------
    # -- compare

    zero_outer_planes_and_equal_times(g4_tau)
    zero_outer_planes_and_equal_times(g40_tau)
    np.testing.assert_array_almost_equal(g4_tau.data, g40_tau.data)
Exemple #10
0
    # -- Exact diagonalization

    fundamental_operators = [
        c(up, 0), c(do, 0),
        c(up, 1), c(do, 1),
        c(up, 2), c(do, 2)
    ]

    ed = TriqsExactDiagonalization(H, fundamental_operators, beta)

    # ------------------------------------------------------------------
    # -- Single-particle Green's functions

    g_tau = GfImTime(name=r'$g$',
                     beta=beta,
                     statistic='Fermion',
                     n_points=50,
                     target_shape=(1, 1))

    g_iwn = GfImFreq(name='$g$',
                     beta=beta,
                     statistic='Fermion',
                     n_points=10,
                     target_shape=(1, 1))

    ed.set_g2_tau(g_tau, c(up, 0), c_dag(up, 0))
    ed.set_g2_iwn(g_iwn, c(up, 0), c_dag(up, 0))

    # ------------------------------------------------------------------
    # -- Two particle Green's functions
Exemple #11
0
from pytriqs.plot.mpl_interface import *
from pytriqs.operators.util.op_struct import get_mkind
from matplotlib.backends.backend_pdf import PdfPages

# Read the reference table file
tau = []
data = []
for line in open("5_plus_5.ref.dat", 'r'):
    cols = line.split()
    tau.append(float(cols[0]))
    data.append([-float(c) for c in cols[1:]])

beta = tau[-1]
n_tau = len(tau)

g_ref = GfImTime(indices=range(len(data[0])), beta=beta, n_points=n_tau)
for nt, d in enumerate(data):
    for nc, val in enumerate(d):
        g_ref.data[nt, nc, nc] = val

for filename in ["5_plus_5.int.h5", "5_plus_5.h5"]:
    # Read the results
    #arch = HDFArchive("5_plus_5.h5",'r')
    #arch = HDFArchive("5_plus_5.int.h5",'r')

    arch = HDFArchive(filename, 'r')
    use_interaction = arch['use_interaction']
    spin_names = arch['spin_names']
    orb_names = arch['orb_names']
    delta_params = arch['delta_params']
Exemple #12
0
def make_calc(beta=2.0, h_field=0.0):

    # ------------------------------------------------------------------
    # -- Hubbard atom with two bath sites, Hamiltonian

    p = ParameterCollection(
        beta=beta,
        V1=2.0,
        V2=5.0,
        epsilon1=0.10,
        epsilon2=3.00,
        h_field=h_field,
        mu=0.0,
        U=5.0,
        ntau=800,
        niw=15,
    )

    # ------------------------------------------------------------------

    print '--> Solving SIAM with parameters'
    print p

    # ------------------------------------------------------------------

    up, do = 'up', 'dn'
    docc = c_dag(up, 0) * c(up, 0) * c_dag(do, 0) * c(do, 0)
    mA = c_dag(up, 0) * c(up, 0) - c_dag(do, 0) * c(do, 0)

    nA = c_dag(up, 0) * c(up, 0) + c_dag(do, 0) * c(do, 0)
    nB = c_dag(up, 1) * c(up, 1) + c_dag(do, 1) * c(do, 1)
    nC = c_dag(up, 2) * c(up, 2) + c_dag(do, 2) * c(do, 2)

    p.H = -p.mu * nA + p.U * docc + p.h_field * mA + \
        p.epsilon1 * nB + p.epsilon2 * nC + \
        p.V1 * (c_dag(up,0)*c(up,1) + c_dag(up,1)*c(up,0) + \
              c_dag(do,0)*c(do,1) + c_dag(do,1)*c(do,0) ) + \
        p.V2 * (c_dag(up,0)*c(up,2) + c_dag(up,2)*c(up,0) + \
              c_dag(do,0)*c(do,2) + c_dag(do,2)*c(do,0) )

    # ------------------------------------------------------------------

    fundamental_operators = [
        c(up, 0), c(do, 0),
        c(up, 1), c(do, 1),
        c(up, 2), c(do, 2)
    ]

    ed = TriqsExactDiagonalization(p.H, fundamental_operators, p.beta)

    g_tau = GfImTime(beta=beta, statistic='Fermion', n_points=400, indices=[0])
    g_iw = GfImFreq(beta=beta, statistic='Fermion', n_points=10, indices=[0])

    p.G_tau = BlockGf(name_list=[up, do],
                      block_list=[g_tau] * 2,
                      make_copies=True)
    p.G_iw = BlockGf(name_list=[up, do],
                     block_list=[g_iw] * 2,
                     make_copies=True)

    ed.set_g2_tau(p.G_tau[up][0, 0], c(up, 0), c_dag(up, 0))
    ed.set_g2_tau(p.G_tau[do][0, 0], c(do, 0), c_dag(do, 0))

    ed.set_g2_iwn(p.G_iw[up][0, 0], c(up, 0), c_dag(up, 0))
    ed.set_g2_iwn(p.G_iw[do][0, 0], c(do, 0), c_dag(do, 0))

    p.magnetization = ed.get_expectation_value(0.5 * mA)

    p.O_tau = Gf(mesh=MeshImTime(beta, 'Fermion', 400), target_shape=[])
    ed.set_g2_tau(p.O_tau, n(up, 0), n(do, 0))
    p.O_tau.data[:] *= -1.

    p.exp_val = ed.get_expectation_value(n(up, 0) * n(do, 0))

    # ------------------------------------------------------------------
    # -- Store to hdf5

    filename = 'data_pyed_h_field_%4.4f.h5' % h_field
    with HDFArchive(filename, 'w') as res:
        res['p'] = p
Exemple #13
0
    else:
        m = None
    m = mpi.bcast(m)

    p = ParameterCollection()
    ed = TriqsExactDiagonalization(m.H, m.op_full, m.beta)

    p.O1_exp = np.zeros((4, 4), dtype=np.complex)
    p.O2_exp = np.zeros((4, 4), dtype=np.complex)
    p.chi_dissconn = np.zeros((4, 4, 4, 4), dtype=np.complex)

    p.chi_static = np.zeros((4, 4, 4, 4), dtype=np.complex)

    p.chi_tau = GfImTime(name=r'$g$',
                         beta=m.beta,
                         statistic='Boson',
                         n_points=50,
                         target_shape=(4, 4, 4, 4))

    p.chi = np.zeros_like(p.chi_static)

    tau = np.array([float(tau) for tau in p.chi_tau.mesh])

    for i1, i2, i3, i4, in itertools.product(range(4), repeat=4):

        print i1, i2, i3, i4

        o1, o2, o3, o4 = m.op_imp[i1], m.op_imp[i2], m.op_imp[i3], m.op_imp[i4]

        O1 = dagger(o1) * o2
        O2 = dagger(o3) * o4