Details for the code.

[yesxiaoyu]

Hello, this is really a nice work, and I just begin to transfer the idea to another task. But I don't really understand the code in my_layers->Average->call->K.sum(x, axis=-2) / K.sum(mask, axis=-2). I just know this class is a layer to compute ys, and the function is to average the weight, and I just find the source code in tensorflow_backend->sum, can't konw axis ues in [-rank(x), rank(x)), why axis=-2. By the way, I'm confused by the mask. Could you please tell me some details to raised me up, thank you.