What is partially monotone layer?
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Suppose that we want to train a neural network model to learn function :math:`f(x,y) = (x^2 + y^2)/2`, which is monotonically increasing with respect to :math:`x` and :math:`y`.
We can use a standard neural network model to learn this function, but we cannot guarantee that the trained neural network model is monotonically increasing with respect to :math:`x` and :math:`y`.

.. image:: square_2d.png

``pmalyer`` libtray provides several neural network layers to handle monotonicity constraints.
Therefore, we can construct a neural network model by using ``pmlayer`` that is guaranteed to be monotonically increasing with respect to :math:`x` and :math:`y`.