def GridSample(inputs, borderMode='repeat'):
    """
    Sample the images using the given coordinates, by bilinear interpolation.
    This was described in the paper:
    `Spatial Transformer Networks <http://arxiv.org/abs/1506.02025>`_.

    This is equivalent to `torch.nn.functional.grid_sample`,
    up to some non-trivial coordinate transformation.

    This implementation returns pixel value at pixel (1, 1) for a floating point coordinate (1.0, 1.0).
    Note that this may not be what you need.

    Args:
        inputs (list): [images, coords]. images has shape NHWC.
            coords has shape (N, H', W', 2), where each pair of the last dimension is a (y, x) real-value
            coordinate.
        borderMode: either "repeat" or "constant" (zero-filled)

    Returns:
        tf.Tensor: a tensor named ``output`` of shape (N, H', W', C).
    """
    image, mapping = inputs
    assert image.get_shape().ndims == 4 and mapping.get_shape().ndims == 4
    input_shape = image.get_shape().as_list()[1:]
    assert None not in input_shape, \
        "Images in GridSample layer must have fully-defined shape"
    assert borderMode in ['repeat', 'constant']

    orig_mapping = mapping
    mapping = tf.maximum(mapping, 0.0)
    lcoor = tf.floor(mapping)
    ucoor = lcoor + 1

    diff = mapping - lcoor
    neg_diff = 1.0 - diff  # bxh2xw2x2

    lcoory, lcoorx = tf.split(lcoor, 2, 3)
    ucoory, ucoorx = tf.split(ucoor, 2, 3)

    lyux = tf.concat([lcoory, ucoorx], 3)
    uylx = tf.concat([ucoory, lcoorx], 3)

    diffy, diffx = tf.split(diff, 2, 3)
    neg_diffy, neg_diffx = tf.split(neg_diff, 2, 3)

    ret = tf.add_n([sample(image, lcoor) * neg_diffx * neg_diffy,
                    sample(image, ucoor) * diffx * diffy,
                    sample(image, lyux) * neg_diffy * diffx,
                    sample(image, uylx) * diffy * neg_diffx], name='sampled')
    if borderMode == 'constant':
        max_coor = tf.constant([input_shape[0] - 1, input_shape[1] - 1], dtype=tf.float32)
        mask = tf.greater_equal(orig_mapping, 0.0)
        mask2 = tf.less_equal(orig_mapping, max_coor)
        mask = tf.logical_and(mask, mask2)  # bxh2xw2x2
        mask = tf.reduce_all(mask, [3])  # bxh2xw2 boolean
        mask = tf.expand_dims(mask, 3)
        ret = ret * tf.cast(mask, tf.float32)
    return tf.identity(ret, name='output')

    Sample the images using the given coordinates, by bilinear interpolation.
    This was described in the paper:
    `Spatial Transformer Networks <http://arxiv.org/abs/1506.02025>`_.

    This is equivalent to `torch.nn.functional.grid_sample`,
    up to some non-trivial coordinate transformation.

    This implementation returns pixel value at pixel (1, 1) for a floating point coordinate (1.0, 1.0).
    Note that this may not be what you need.

    Args:
        inputs (list): [images, coords]. images has shape NHWC.
            coords has shape (N, H', W', 2), where each pair of the last dimension is a (y, x) real-value
            coordinate.
        borderMode: either "repeat" or "constant" (zero-filled)

    Returns:
        tf.Tensor: a tensor named ``output`` of shape (N, H', W', C).
    
examples/SpatialTransformer/mnist-addition.py