# How to perform element-wise subtraction on tensors in PyTorch?

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To perform element-wise subtraction on tensors, we can use the torch.sub() method of PyTorch. The corresponding elements of the tensors are subtracted. We can subtract a scalar or tensor from another tensor. We can subtract a tensor from a tensor with same or different dimension. The dimension of the final tensor will be same as the dimension of the higher-dimensional tensor.

## Steps

• Import the required library. In all the following Python examples, the required Python library is torch. Make sure you have already installed it.

• Define two or more PyTorch tensors and print them. If you want to subtract a scalar quantity, define it.

• Subtract a scalar or a tensor from another tensor using torch.sub() and assign the value to a new variable. You can also subtract a scalar quantity from the tensor. Subtracting the tensors using this method does not make any change in the original tensors.

• Print the final tensor.

## Example 1

Here, we will have a Python 3 program to subtract a scalar quantity from a tensor. We will see three different ways to perform the same task.

# Python program to perform element-wise subtraction
# import the required library
import torch

# Create a tensor
t = torch.Tensor([1.5, 2.03, 3.8, 2.9])
print("Original Tensor t:", t)

# Subtract a scalar value to a tensor
v = torch.sub(t, 5.60)
print("Element-wise subtraction result:", v)

# Same result can also be obtained as below
t1 = torch.Tensor([5.60])
w = torch.sub(t, t1)
print("Element-wise subtraction result:", w)

# Other way to do above operation
t2 = torch.Tensor([5.60,5.60,5.60,5.60])
x = torch.sub(t, t2)
print("Element-wise subtraction result:", x)

## Output

Original Tensor t:
tensor([1.5000, 2.0300, 3.8000, 2.9000])
Element-wise subtraction result:
tensor([-4.1000, -3.5700, -1.8000, -2.7000])
Element-wise subtraction result:
tensor([-4.1000, -3.5700, -1.8000, -2.7000])
Element-wise subtraction result:
tensor([-4.1000, -3.5700, -1.8000, -2.7000])

## Example 2

The following program shows how to subtract a 1-D tensor from a 2-D tensor.

# Import necessary library
import torch

# Create a 2D tensor
T1 = torch.Tensor([[8,7],[4,5]])

# Create a 1-D tensor
T2 = torch.Tensor([10, 5])
print("T1:", T1)
print("T2:", T2)

# Subtract 1-D tensor from 2-D tensor
v = torch.sub(T1, T2)
print("Element-wise subtraction result:", v)

## Output

T1:
tensor([[8., 7.],
[4., 5.]])
T2:
tensor([10., 5.])
Element-wise subtraction result:
tensor([[-2., 2.],
[-6., 0.]])

## Example 3

The following program shows how to subtract a 2D tensor from a 1D tensor.

# Python program to subtract 2D tensor from 1D tensor
# Import the library
import torch

# Create a 2D tensor
T1 = torch.Tensor([[1,2],[4,5]])

# Create a 1-D tensor
T2 = torch.Tensor([10, 5])
print("T1:", T1)
print("T2:", T2)

# Subtract 2-D tensor from 1-D tensor
v = torch.sub(T2, T1)
print("Element-wise subtraction result:", v)

## Output

T1:
tensor([[1., 2.],
[4., 5.]])
T2:
tensor([10., 5.])
Element-wise subtraction result:
tensor([[9., 3.],
[6., 0.]])

You can notice that the final tensor is a 2D tensor.

## Example 4

The following program shows how to subtract a 2D tensor from a 2D tensor.

# import the library
import torch

# Create two 2-D tensors
T1 = torch.Tensor([[8,7],[3,4]])
T2 = torch.Tensor([[0,3],[4,9]])
print("T1:", T1)
print("T2:", T2)

# Subtract above two 2-D tensors
v = torch.sub(T1,T2)
print("Element-wise subtraction result:", v)

## Output

T1:
tensor([[8., 7.],
[3., 4.]])
T2:
tensor([[0., 3.],
[4., 9.]])
Element-wise subtraction result:
tensor([[ 8., 4.],
[-1., -5.]])
Updated on 06-Nov-2021 09:47:54