chainerx.conv

chainerx.conv(x, w, b=None, stride=1, pad=0, cover_all=False)

N-dimensional convolution.

This is an implementation of N-dimensional convolution which is generalized two-dimensional convolution in ConvNets. It takes three arrays: the input x, the filter weight w and the bias vector b.

Notation: here is a notation for dimensionalities.

  • \(N\) is the number of spatial dimensions.

  • \(n\) is the batch size.

  • \(c_I\) and \(c_O\) are the number of the input and output channels, respectively.

  • \(d_1, d_2, ..., d_N\) are the size of each axis of the input’s spatial dimensions, respectively.

  • \(k_1, k_2, ..., k_N\) are the size of each axis of the filters, respectively.

  • \(l_1, l_2, ..., l_N\) are the size of each axis of the output’s spatial dimensions, respectively.

  • \(p_1, p_2, ..., p_N\) are the size of each axis of the spatial padding size, respectively.

Then the conv function computes correlations between filters and patches of size \((k_1, k_2, ..., k_N)\) in x. Note that correlation here is equivalent to the inner product between expanded tensors. Patches are extracted at positions shifted by multiples of stride from the first position (-p_1, -p_2, ..., -p_N) for each spatial axis.

Let \((s_1, s_2, ..., s_N)\) be the stride of filter application. Then, the output size \((l_1, l_2, ..., l_N)\) is determined by the following equations:

\[l_n = (d_n + 2p_n - k_n) / s_n + 1 \ \ (n = 1, ..., N)\]

If cover_all option is True, the filter will cover the all spatial locations. So, if the last stride of filter does not cover the end of spatial locations, an additional stride will be applied to the end part of spatial locations. In this case, the output size is determined by the following equations:

\[l_n = (d_n + 2p_n - k_n + s_n - 1) / s_n + 1 \ \ (n = 1, ..., N)\]
Parameters

  • x (ndarray) – Input array of shape \((n, c_I, d_1, d_2, ..., d_N)\).

  • w (ndarray) – Weight array of shape \((c_O, c_I, k_1, k_2, ..., k_N)\).

  • b (None or ndarray) – One-dimensional bias array with length \(c_O\) (optional).

  • stride (int or tuple of int s) – Stride of filter applications \((s_1, s_2, ..., s_N)\). stride=s is equivalent to (s, s, ..., s).

  • pad (int or tuple of int s) – Spatial padding width for input arrays \((p_1, p_2, ..., p_N)\). pad=p is equivalent to (p, p, ..., p).

  • cover_all (bool) – If True, all spatial locations are convoluted into some output pixels. It may make the output size larger. cover_all needs to be False if you want to use cuda backend.

Returns

Output array of shape \((n, c_O, l_1, l_2, ..., l_N)\).

Return type

ndarray

Note

In cuda backend, this function uses cuDNN implementation for its forward and backward computation.

Note

In cuda backend, this function has following limitations yet:

  • The cover_all=True option is not supported yet.

  • The dtype must be float32 or float64 (float16 is not supported yet.)

Note

During backpropagation, this function propagates the gradient of the output array to input arrays x, w, and b.

See also

chainer.functions.convolution_nd()

Example

>>> n = 10
>>> c_i, c_o = 3, 1
>>> d1, d2, d3 = 30, 40, 50
>>> k1, k2, k3 = 10, 10, 10
>>> p1, p2, p3 = 5, 5, 5
>>> x = chainerx.random.uniform(0, 1, (n, c_i, d1, d2, d3)).astype(np.float32)
>>> x.shape
(10, 3, 30, 40, 50)
>>> w = chainerx.random.uniform(0, 1, (c_o, c_i, k1, k2, k3)).astype(np.float32)
>>> w.shape
(1, 3, 10, 10, 10)
>>> b = chainerx.random.uniform(0, 1, (c_o)).astype(np.float32)
>>> b.shape
(1,)
>>> s1, s2, s3 = 2, 4, 6
>>> y = chainerx.conv(x, w, b, stride=(s1, s2, s3), pad=(p1, p2, p3))
>>> y.shape
(10, 1, 16, 11, 9)
>>> l1 = int((d1 + 2 * p1 - k1) / s1 + 1)
>>> l2 = int((d2 + 2 * p2 - k2) / s2 + 1)
>>> l3 = int((d3 + 2 * p3 - k3) / s3 + 1)
>>> y.shape == (n, c_o, l1, l2, l3)
True
>>> y = chainerx.conv(x, w, b, stride=(s1, s2, s3), pad=(p1, p2, p3), cover_all=True)
>>> y.shape == (n, c_o, l1, l2, l3 + 1)
True