Computes the (approximate) normal vector of the input triangle.

    :param tri: triangle object
    :type tri: elements.Triangle
    :return: normal vector of the triangle
    :rtype: tuple

def triangle_normal(tri):
    """ Computes the (approximate) normal vector of the input triangle.

    :param tri: triangle object
    :type tri: elements.Triangle
    :return: normal vector of the triangle
    :rtype: tuple
    """
    vec1 = vector_generate(tri.vertices[0].data, tri.vertices[1].data)
    vec2 = vector_generate(tri.vertices[1].data, tri.vertices[2].data)
    return vector_cross(vec1, vec2)