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torch.nn.functional.pad

torch.nn.functional.pad(input, pad, mode='constant', value=0)

Pads tensor.

Padding size:

The padding size by which to pad some dimensions of input are described starting from the last dimension and moving forward. len(pad)2\left\lfloor\frac{\text{len(pad)}}{2}\right\rfloor dimensions of input will be padded. For example, to pad only the last dimension of the input tensor, then pad has the form (padding_left,padding_right)(\text{padding\_left}, \text{padding\_right}) ; to pad the last 2 dimensions of the input tensor, then use (padding_left,padding_right,(\text{padding\_left}, \text{padding\_right}, padding_top,padding_bottom)\text{padding\_top}, \text{padding\_bottom}) ; to pad the last 3 dimensions, use (padding_left,padding_right,(\text{padding\_left}, \text{padding\_right}, padding_top,padding_bottom\text{padding\_top}, \text{padding\_bottom} padding_front,padding_back)\text{padding\_front}, \text{padding\_back}) .

Padding mode:

See torch.nn.ConstantPad2d, torch.nn.ReflectionPad2d, and torch.nn.ReplicationPad2d for concrete examples on how each of the padding modes works. Constant padding is implemented for arbitrary dimensions. Replicate padding is implemented for padding the last 3 dimensions of 5D input tensor, or the last 2 dimensions of 4D input tensor, or the last dimension of 3D input tensor. Reflect padding is only implemented for padding the last 2 dimensions of 4D input tensor, or the last dimension of 3D input tensor.

Note

When using the CUDA backend, this operation may induce nondeterministic behaviour in its backward pass that is not easily switched off. Please see the notes on Reproducibility for background.

Parameters
  • input (Tensor) – N-dimensional tensor

  • pad (tuple) – m-elements tuple, where m2\frac{m}{2} \leq input dimensions and mm is even.

  • mode'constant', 'reflect', 'replicate' or 'circular'. Default: 'constant'

  • value – fill value for 'constant' padding. Default: 0

Examples:

>>> t4d = torch.empty(3, 3, 4, 2)
>>> p1d = (1, 1) # pad last dim by 1 on each side
>>> out = F.pad(t4d, p1d, "constant", 0)  # effectively zero padding
>>> print(out.size())
torch.Size([3, 3, 4, 4])
>>> p2d = (1, 1, 2, 2) # pad last dim by (1, 1) and 2nd to last by (2, 2)
>>> out = F.pad(t4d, p2d, "constant", 0)
>>> print(out.size())
torch.Size([3, 3, 8, 4])
>>> t4d = torch.empty(3, 3, 4, 2)
>>> p3d = (0, 1, 2, 1, 3, 3) # pad by (0, 1), (2, 1), and (3, 3)
>>> out = F.pad(t4d, p3d, "constant", 0)
>>> print(out.size())
torch.Size([3, 9, 7, 3])

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