for i in range(0, len(f)):
        e0 = v[f[i][0]]
        e1 = v[f[i][1]]
        e2 = v[f[i][2]]
        a = e0 - e1
        b = e2 - e0
        c = e1 - e2
        orthe0 = np.cross(a, b) / np.linalg.norm(np.cross(a, b))
        gradient[f[i][0]] = gradient[f[i][0]] + np.cross(c, orthe0)
        orthe1 = np.cross(c, a) / np.linalg.norm(np.cross(c, a))
        gradient[f[i][1]] = gradient[f[i][1]] + np.cross(b, orthe1)
        orthe2 = np.cross(b, c) / np.linalg.norm(np.cross(b, c))
        gradient[f[i][2]] = gradient[f[i][2]] + np.cross(a, orthe2)

    return gradient