How to use the nexusformat.nexus.tree.centers function in nexusformat

def convert_QE(self):
        """Convert S(phi,eps) to S(Q,eps)"""

        self.read_parameters()

        Ei = self.Ei
        dQ = self.dQ
        dE = self.dE

        pol, tof = centers(self.entry['data'].nxsignal, self.entry['data'].nxaxes)
        en = self.convert_tof(tof)

        idx_max = min(np.where(np.abs(en-0.75*Ei)<0.1)[0])

        en = en[:idx_max]

        data = self.entry['data'].nxsignal.nxdata[:,:idx_max]
        if self.entry['data'].nxerrors:
            errors = self.entry['data'].nxerrors.nxdata[:]

        Q = np.zeros((len(pol), len(en)))
        E = np.zeros((len(pol), len(en)))

        for i in range(0,len(pol)):
            p = pol[i]
            Q[i,:] = np.array(np.sqrt((2*Ei - en - 2*np.sqrt(Ei*(Ei-en))

def convert_QE(self):
        """Convert S(phi,eps) to S(Q,eps)"""

        self.read_parameters()

        Ei = self.Ei
        dQ = self.dQ
        dE = self.dE

        pol, tof = centers(self.entry['data'].nxsignal, self.entry['data'].nxaxes)
        en = self.convert_tof(tof)

        idx_max = min(np.where(np.abs(en-0.75*Ei)<0.1)[0])

        en = en[:idx_max]

        data = self.entry['data'].nxsignal.nxdata[:,:idx_max]
        if self.entry['data'].nxerrors:
            errors = self.entry['data'].nxerrors.nxdata[:]

        Q = np.zeros((len(pol), len(en)))
        E = np.zeros((len(pol), len(en)))

        for i in range(0,len(pol)):
            p = pol[i]
            Q[i,:] = np.array(np.sqrt((2*Ei - en - 2*np.sqrt(Ei*(Ei-en))

def convert_QE(entry, dQ, dE):
    """Convert S(phi,eps) to S(Q,eps)"""
    az = entry.data.azimuthal.nxdata[:]
    pol = entry.data.polar.nxdata[:]
    pol, en = centers(entry.data.nxsignal, entry.data.nxaxes)
    data = entry.data.data.nxdata[:]
    errors = entry.data.errors.nxdata[:]

    Ei = entry.instrument.monochromator.incident_energy.nxdata

    Q = np.zeros((len(pol), len(en)))
    E = np.zeros((len(pol), len(en)))

    for i in range(0,len(pol)):
        for j in range(0,len(en)):
            Q[i][j] = np.sqrt((2*Ei - en[j] - 2*np.sqrt(Ei*(Ei-en[j])) 
                               * np.cos(pol[i]*np.pi/180.0))/2.0721)
            E[i][j]=en[j]

    s = Q.shape
    Qin = Q.reshape(s[0]*s[1])