def fusion_mul(map, feat):
    """
    Args:
        map: tensor size = bs, c1, h, w
        feat: tensor size = bs, c2, h, w

    Returns:
        weighted_feat size = (bs, c1 x c2, h, w)
    """
    bs, c1, h, w = map.size()
    c2 = feat.size(1)
    rlt = map.view(bs, c1, 1, h, w) * feat.view(bs, 1, c2, h, w)
    rlt = rlt.view(bs, c1 * c2, h, w)
    return rlt