calculate transport matrix

        :param gamma: electron energy measured by mc^2
        :return: transport matrix
        :rtype: numpy array

def calcTransM(self, gamma=None):
        """calculate transport matrix

        :param gamma: electron energy measured by mc^2
        :return: transport matrix
        :rtype: numpy array
        """
        sconf = self.getConfig(type='simu')
        if 'l' in sconf:
            l = float(sconf['l'])
        else:
            l = 0
        self.transM = mathutils.transDrift(l, gamma)
        self.transM_flag = True
        return self.transM