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# How to perform an expand operation in PyTorch?

**Tensor.expand()** attribute is used to perform expand operation. It expands the Tensor to new dimensions along the singleton dimension.

Expanding a tensor only creates a new view of the original tensor; it doesn't make a copy of the original tensor.

If you set a particular dimension as -1, the tensor will not be expanded along this dimension.

For example, if we have a tensor of size (3,1), we can expand this tensor along the dimension of size 1.

## Steps

To expand a tensor, one could follow the steps given below −

Import the torch library. Make sure you have already installed it.

import torch

Define a tensor having at least one dimension as singleton.

t = torch.tensor([[1],[2],[3]])

Expand the tensor along the singleton dimension. Expanding along a non-singleton dimension will throw a Runtime Error (see Example 3).

t_exp = t.expand(3,2)

Display the expanded tensor.

print("Tensor after expand:

", t_exp)

## Example 1

The following Python program shows how to expand a tensor of size (3,1) to a tensor of size (3,2). It expands the tensor along the dimension size of 1. The other dimension of size 3 remains unchanged.

# import required libraries import torch # create a tensor t = torch.tensor([[1],[2],[3]]) # display the tensor print("Tensor:

", t) print("Size of Tensor:

", t.size()) # expand the tensor exp = t.expand(3,2) print("Tensor after expansion:

", exp)

## Output

Tensor: tensor([[1], [2], [3]]) Size of Tensor: torch.Size([3, 1]) Tensor after expansion: tensor([[1, 1], [2, 2], [3, 3]])

## Example 2

The following Python program expands a tensor of size (1,3) to a tensor of size (3,3). It expands the tensor along the dimension size of 1.

# import required libraries import torch # create a tensor t = torch.tensor([[1,2,3]]) # display the tensor print("Tensor:

", t) # size of tensor is [1,3] print("Size of Tensor:

", t.size()) # expand the tensor expandedTensor = t.expand(3,-1) print("Expanded Tensor:

", expandedTensor) print("Size of expanded tensor:

", expandedTensor.size())

## Output

Tensor: tensor([[1, 2, 3]]) Size of Tensor: torch.Size([1, 3]) Expanded Tensor: tensor([[1, 2, 3], [1, 2, 3], [1, 2, 3]]) Size of expanded tensor: torch.Size([3, 3])

## Example 3

In the following Python program, we tried to expand the tensor along a nonsingleton dimension, hence it throws a Runtime Error.

# import required libraries import torch # create a tensor t = torch.tensor([[1,2,3]]) # display the tensor print("Tensor:

", t) # size of tensor is [1,3] print("Size of Tensor:

", t.size()) t.expand(3,4)

## Output

Tensor: tensor([[1, 2, 3]]) Size of Tensor: torch.Size([1, 3]) RuntimeError: The expanded size of the tensor (4) must match the existing size (3) at non-singleton dimension 1. Target sizes: [3, 4]. Tensor sizes: [1, 3]

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