import numpy as np


def getKeff(pm, k, pbc, Nz):

    nx = k.shape[2]  # Pasar k sin bordes de k=0
    ny = k.shape[1]

    tz = 2 * k[1, :, :] * k[0, :, :] / (k[0, :, :] + k[1, :, :])
    q = ((pm[0, :, :] - pm[1, :, :]) * tz).sum()
    area = ny * nx
    l = Nz
    keff = q * l / (pbc * area)
    return keff, q