nn_conv1d {torch}

Conv1D module

Description

Applies a 1D convolution over an input signal composed of several input planes. In the simplest case, the output value of the layer with input size (N, C_{\mbox{in}}, L) and output (N, C_{\mbox{out}}, L_{\mbox{out}}) can be precisely described as:

Usage

nn_conv1d(
  in_channels,
  out_channels,
  kernel_size,
  stride = 1,
  padding = 0,
  dilation = 1,
  groups = 1,
  bias = TRUE,
  padding_mode = "zeros"
)

Arguments

in_channels

(int): Number of channels in the input image

out_channels

(int): Number of channels produced by the convolution

kernel_size

(int or tuple): Size of the convolving kernel

stride

(int or tuple, optional): Stride of the convolution. Default: 1

padding

(int, tuple or str, optional) – Padding added to both sides of the input. Default: 0

dilation

(int or tuple, optional): Spacing between kernel elements. Default: 1

groups

(int, optional): Number of blocked connections from input channels to output channels. Default: 1

bias

(bool, optional): If TRUE, adds a learnable bias to the output. Default: TRUE

padding_mode

(string, optional): 'zeros', 'reflect', 'replicate' or 'circular'. Default: 'zeros'

Details

\mbox{out}(N_i, C_{\mbox{out}_j}) = \mbox{bias}(C_{\mbox{out}_j}) + \sum_{k = 0}^{C_{in} - 1} \mbox{weight}(C_{\mbox{out}_j}, k) \star \mbox{input}(N_i, k)

where \star is the valid cross-correlation operator, N is a batch size, C denotes a number of channels, L is a length of signal sequence.

• stride controls the stride for the cross-correlation, a single number or a one-element tuple.

• padding controls the amount of implicit zero-paddings on both sides for padding number of points.

• dilation controls the spacing between the kernel points; also known as the à trous algorithm. It is harder to describe, but this link has a nice visualization of what dilation does.

• groups controls the connections between inputs and outputs. in_channels and out_channels must both be divisible by groups. For example,

  • At groups=1, all inputs are convolved to all outputs.

  • At groups=2, the operation becomes equivalent to having two conv layers side by side, each seeing half the input channels, and producing half the output channels, and both subsequently concatenated.

  • At groups= in_channels, each input channel is convolved with its own set of filters, of size \left\lfloor\frac{out\_channels}{in\_channels}\right\rfloor.

Note

Depending of the size of your kernel, several (of the last) columns of the input might be lost, because it is a valid cross-correlation, and not a full cross-correlation. It is up to the user to add proper padding.

When groups == in_channels and out_channels == K * in_channels, where K is a positive integer, this operation is also termed in literature as depthwise convolution. In other words, for an input of size (N, C_{in}, L_{in}), a depthwise convolution with a depthwise multiplier K, can be constructed by arguments (C_{\mbox{in}}=C_{in}, C_{\mbox{out}}=C_{in} \times K, ..., \mbox{groups}=C_{in}).

Shape

• Input: (N, C_{in}, L_{in})

• Output: (N, C_{out}, L_{out}) where

L_{out} = \left\lfloor\frac{L_{in} + 2 \times \mbox{padding} - \mbox{dilation} \times (\mbox{kernel\_size} - 1) - 1}{\mbox{stride}} + 1\right\rfloor

Attributes

• weight (Tensor): the learnable weights of the module of shape (\mbox{out\_channels}, \frac{\mbox{in\_channels}}{\mbox{groups}}, \mbox{kernel\_size}). The values of these weights are sampled from \mathcal{U}(-\sqrt{k}, \sqrt{k}) where k = \frac{groups}{C_{\mbox{in}} * \mbox{kernel\_size}}

• bias (Tensor): the learnable bias of the module of shape (out_channels). If bias is TRUE, then the values of these weights are sampled from \mathcal{U}(-\sqrt{k}, \sqrt{k}) where k = \frac{groups}{C_{\mbox{in}} * \mbox{kernel\_size}}

Examples

if (torch_is_installed()) {
m <- nn_conv1d(16, 33, 3, stride = 2)
input <- torch_randn(20, 16, 50)
output <- m(input)
}