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from chainer.functions.connection import local_convolution_2d
from chainer import initializers
from chainer import link
from chainer import variable
def _pair(x):
if hasattr(x, '__getitem__'):
return x
return x, x
def _conv_output_length(input_length, filter_size, stride):
output_length = input_length - filter_size + 1
return output_length
class LocalConvolution2D(link.Link):
"""Two-dimensional local convolutional layer.
This link wraps the :func:`~chainer.functions.local_convolution_2d`
function and holds the filter weight and bias array as parameters.
Args:
in_channels (int): Number of channels of input arrays. If either
in_channels or in_size is ``None``,
parameter initialization will be deferred until the first forward
data pass at which time the size will be determined.
out_channels (int): Number of channels of output arrays
in_size (int or pair of ints): Size of each image channel
``in_size=k`` and ``in_size=(k,k)`` are equivalent. If either
in_channels or in_size is ``None``, parameter initialization will
be deferred until the first forward data pass when the size will be
determined.
ksize (int or pair of ints): Size of filters (a.k.a. kernels).
``ksize=k`` and ``ksize=(k, k)`` are equivalent.
stride (int or pair of ints): Stride of filter applications.
``stride=s`` and ``stride=(s, s)`` are equivalent.
nobias (bool): If ``True``, then this link does not use the bias term.
initialW (:ref:`initializer <initializer>`): Initializer to
initialize the weight. When it is :class:`numpy.ndarray`,
its ``ndim`` should be 6.
initial_bias (:ref:`initializer <initializer>`): Initializer to
initialize the bias. If ``None``, the bias will be initialized to
zero. When it is :class:`numpy.ndarray`, its ``ndim`` should be 3.
.. seealso::
See :func:`chainer.functions.local_convolution_2d`.
Attributes:
W (~chainer.Variable): Weight parameter.
b (~chainer.Variable): Bias parameter.
"""
def __init__(self, in_channels, out_channels, in_size=None, ksize=None,
stride=1, nobias=False, initialW=None, initial_bias=None,
**kwargs):
super(LocalConvolution2D, self).__init__()
self.ksize = ksize
self.stride = _pair(stride)
self.nobias = nobias
self.out_channels = out_channels
with self.init_scope():
W_initializer = initializers._get_initializer(initialW)
self.W = variable.Parameter(W_initializer)
if nobias:
self.b = None
else:
if initial_bias is None:
initial_bias = 0
bias_initializer = initializers._get_initializer(initial_bias)
self.b = variable.Parameter(bias_initializer)
if in_channels is not None and in_size is not None:
self._initialize_params(in_channels, _pair(in_size))
def _initialize_params(self, in_channels, in_size):
kh, kw = _pair(self.ksize)
ih, iw = _pair(in_size)
oh = _conv_output_length(ih, kh, self.stride[0])
ow = _conv_output_length(iw, kw, self.stride[1])
W_shape = (self.out_channels, oh, ow, in_channels, kh, kw)
bias_shape = (self.out_channels, oh, ow,)
self.W.initialize(W_shape)
if not self.nobias:
self.b.initialize(bias_shape)
def forward(self, x):
"""Applies the local convolution layer.
Args:
x (~chainer.Variable): Input image.
Returns:
~chainer.Variable: Output of the convolution.
"""
if self.W.array is None:
self._initialize_params(x.shape[1], x.shape[2:])
return local_convolution_2d.local_convolution_2d(
x, self.W, self.b, self.stride)
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