def draw_neural_network(
    axes        = None,
    left        = None,
    right       = None,
    bottom      = None,
    top         = None,
    layer_sizes = None
    ):
    """
    # abstract

    This function draws a neural network representation diagram using
    matplotilb.

    # arguments

    |*argument* |*description*                                                 |
    |-----------|--------------------------------------------------------------|
    |axes       |matplotlib.axes.AxesSubplot: the axes on which to plot the    |
    |           |diagram (returned by matplotlib.pyplot.gca())                 |
    |left       |float: the position of the centers of the left nodes          |
    |right      |float: the position of the centers of the right nodes         |
    |bottom     |float: the position of the centers of the bottom nodes        |
    |top        |float: the position of the centers of the top nodes           |
    |layer_sizes|list of integers: list of layer sizes, including input and    |
    |           |output dimensionality                                         |

    # example

    ```Python
    figure = matplotlib.pyplot.figure(figsize = (12, 12))
    abstraction.draw_neural_network(
        axes        = figure.gca(),
        left        = .1,
        right       = .9,
        bottom      = .1,
        top         = .9,
        layer_sizes = [4, 7, 2]
    )
    figure.savefig("neural_network_diagram.png")
    ```
    """
    spacing_vertical   = (top - bottom) / float(max(layer_sizes))
    spacing_horizontal = (right - left) / float(len(layer_sizes) - 1)
    # nodes
    for n, layer_size in enumerate(layer_sizes):
        layer_top = spacing_vertical * (layer_size - 1)/2 + (top + bottom) / 2
        for m in xrange(layer_size):
            circle = matplotlib.pyplot.Circle(
                (
                    n * spacing_horizontal + left,
                    layer_top - m * spacing_vertical
                ),
                spacing_vertical / 4,
                color  = "w",
                ec     = "k",
                zorder = 4
            )
            axes.add_artist(circle)
    # edges
    for n, (layer_size_a, layer_size_b) in enumerate(zip(
        layer_sizes[:-1],
        layer_sizes[1:]
        )):
        layer_top_a =\
            spacing_vertical * (layer_size_a - 1) / 2 + (top + bottom) / 2
        layer_top_b =\
            spacing_vertical * (layer_size_b - 1) / 2 + (top + bottom) / 2
        for m in xrange(layer_size_a):
            for o in xrange(layer_size_b):
                line = matplotlib.pyplot.Line2D(
                    [
                        n * spacing_horizontal + left,
                        (n + 1) * spacing_horizontal + left
                    ],
                    [
                        layer_top_a - m * spacing_vertical,
                        layer_top_b - o * spacing_vertical
                    ],
                    c = "k"
                )
                axes.add_artist(line)