import numpy as np

from ase.dft.stm import STM
from ase.dft.dos import DOS
from ase.dft.wannier import Wannier
from ase.dft.kpoints import monkhorst_pack


def get_distribution_moment(x, y, order=0):
    """Return the moment of nth order of distribution.
    
    1st and 2nd order moments of a band correspond to the band's
    center and width respectively.
    
    For integration, the trapezoid rule is used.
    """

    x = np.asarray(x)
    y = np.asarray(y)
        
    if order == 0:
        return np.trapz(y, x)
    elif isinstance(order, int):
        return np.trapz(x**order * y, x) / np.trapz(y, x)
    elif hasattr(order, '__iter__'):
        return [get_distribution_moment(x, y, n) for n in order]
    else:
        raise ValueError('Illegal order: %s' % order)

