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# How to Perform Basic Matrix Operations with Pytorch Tensor

In this Notebook, I try to Explain Basic Matrix Operations using PyTorch tensor.

### Lets Discuss Tensor First!

Tensor is a multi-dimensional matrix containing elements of a single data type.
like tensor is multidimensional so you can Easily handle number Which is a zero-dimensional matrix, vector Which is a single-dimensional matrix, matrix Which is a two-dimensional matrix, or multi-dimensions matrix.

``````# Import torch and other required modules
import torch
``````
``````# Number
t1 = torch.tensor(9.)
t1
``````
``````tensor(9.)
``````
``````# vector
t2 = torch.tensor([1,2,3,4,5])
t2

``````
``````tensor([1, 2, 3, 4, 5])
``````
``````# matrix
t3 = torch.tensor([[2., 6],
[8, 9],
[9, 4]])
t3
``````
``````tensor([[2., 6.],
[8., 9.],
[9., 4.]])
``````
``````# n-dimentional
t4 = torch.tensor([[[11., 12., 13.],
[13., 14., 15.]],

[[15., 16., 17.],
[17., 18., 19.]]])
t4
``````
``````tensor([[[11., 12., 13.],
[13., 14., 15.]],

[[15., 16., 17.],
[17., 18., 19.]]])
``````

In the ML/DL you can use CPU or GPU for processing and torch can handle both devices with using torch.device for more detail go to https://pytorch.org/docs/stable/tensors.html

## Let's Discuss Matrix and Operations of Matrix

### Matrix

In mathematics, a matrix is a rectangular array of numbers, symbols, or expressions, arranged in rows and columns. --Wikipedia Image Source: Wikipedia
In the above matrix, you can see an m × n matrix: The m is the number of Horizontal are rows and the n is verticals are columns. In the matrix, each element is denoted by a variable with two subscripts like a 2,1 that means second row and first column

The Ml/DL matrix is very important because with matrix data handling and representation are very easy so Pytorch provides a tensor for handling matrix or higher dimensional matrix as I discussed above.
now Let's discuss a different type of matrix and how to create and handle with tensor

### Matrix Operations

Scalar Operations

• Subtraction
• Multiplication
• division
• other mathematical function

Matrix Operations (in the addition, subtraction, scalar matrix Multiplication snd division must be dimension order is same)

• Subtraction of Matrices
• scaler Multiplication of Matrices
• scaler Multiplication of Matrices
• Multiplication of Matrices

https://byjus.com/jee/matrix-operations/

``````# for example let's take 2x4 matrix
x = torch.randn((2,3))

x, x.shape

``````
``````(tensor([[-2.7610e-01,  7.4592e-01,  4.8388e-01],
[ 8.7141e-01, -6.2898e-04,  8.8964e-01]]), torch.Size([2, 3]))
``````
``````y = torch.randn((2,3))
y, x.shape
``````
``````(tensor([[-0.3368, -0.8528, -0.3528],
[ 0.4487, -1.1638, -0.8607]]), torch.Size([2, 3]))
``````

### Scaler Opretions of Matrix

#### Addition of scaler number with matrix element

``````# add constant with matrix
x+2
``````
``````tensor([[1.7239, 2.7459, 2.4839],
[2.8714, 1.9994, 2.8896]])
``````
``````2*x
``````
``````tensor([[-5.5220e-01,  1.4918e+00,  9.6776e-01],
[ 1.7428e+00, -1.2580e-03,  1.7793e+00]])
``````

#### Subtract scaler number with matrix element

``````# Subtract constant with matrix
x-2
``````
``````tensor([[-2.2761, -1.2541, -1.5161],
[-1.1286, -2.0006, -1.1104]])
``````

#### Multiplication of scaler number with matrix element

``````x*3
``````
``````tensor([[-8.2830e-01,  2.2377e+00,  1.4516e+00],
[ 2.6142e+00, -1.8869e-03,  2.6689e+00]])
``````
``````x*-1
``````
``````tensor([[ 2.7610e-01, -7.4592e-01, -4.8388e-01],
[-8.7141e-01,  6.2898e-04, -8.8964e-01]])
``````

#### Division of scaler number with matrix element

``````x/2
``````
``````tensor([[-1.3805e-01,  3.7296e-01,  2.4194e-01],
[ 4.3571e-01, -3.1449e-04,  4.4482e-01]])
``````

#### Absolute Function

``````torch.abs(x)
``````
``````tensor([[2.7610e-01, 7.4592e-01, 4.8388e-01],
[8.7141e-01, 6.2898e-04, 8.8964e-01]])
``````

#### Ceiling

``````torch.ceil(x)
``````
``````tensor([[-0., 1., 1.],
[1., -0., 1.]])
``````

Similarly, you can use other math functions like Cos(x), sin(x), etc.

## Matrix opretions

``````m1 = torch.tensor([[2., 6],
[8, 9],
[9, 4]])
m1
``````
``````tensor([[2., 6.],
[8., 9.],
[9., 4.]])
``````
``````m2 = torch.tensor([[1., 6],
[8, 4],
[3, 4]])
m2
``````
``````tensor([[1., 6.],
[8., 4.],
[3., 4.]])
``````

``````# add self witch is similar  to 2*m1
m1+m1
``````
``````tensor([[ 4., 12.],
[16., 18.],
[18.,  8.]])
``````
``````m1+m2
``````
``````tensor([[ 3., 12.],
[16., 13.],
[12.,  8.]])
``````

#### Subtraction of Matrices

``````m1-m2
``````
``````tensor([[1., 0.],
[0., 5.],
[6., 0.]])
``````
``````# Subtract with self
x-x
``````
``````tensor([[0., 0., 0.],
[0., 0., 0.]])
``````

#### Division of Matrices

``````# this is scaler Multiplication don't be confused with matrix Multiplication. in scaler, Multiplication must be the dimensions  are the same
x*x
``````
``````tensor([[7.6231e-02, 5.5639e-01, 2.3414e-01],
[7.5936e-01, 3.9561e-07, 7.9146e-01]])
``````
``````x*y
``````
``````tensor([[ 9.2995e-02, -6.3612e-01, -1.7071e-01],
[ 3.9101e-01,  7.3199e-04, -7.6575e-01]])
``````

#### Division of Matrices

``````x/x
``````
``````tensor([[1., 1., 1.],
[1., 1., 1.]])
``````
``````x/y
``````
``````tensor([[ 8.1973e-01, -8.7466e-01, -1.3716e+00],
[ 1.9420e+00,  5.4046e-04, -1.0336e+00]])
``````

#### Multiplication of Matrices

If X and Y are matrix and X has dimensions m×n and Y have dimensions n×p, then the product of X and Y has dimensions m×p.
The entry (XY)ij is obtained by multiplying row I of X by column j of Y, which is done by multiplying corresponding entries together and then adding the results: Images Sauce:chem.libretexts.org

For Matrix multipication you can use @ oprator and * oparetor is scaler multipication

``````#let's take X
X = torch.tensor([[2., 6],
[8, 9],
[9, 4]])
X, X.shape
``````
``````(tensor([[2., 6.],
[8., 9.],
[9., 4.]]), torch.Size([3, 2]))
``````
``````#let's take X
Y = torch.tensor([[2., 6, 9],
[8, 9, 4]])
, X.shape
``````
``````'X.shape'
``````
``````#multiply X ans Y
X@Y
``````
``````tensor([[ 52.,  66.,  42.],
[ 88., 129., 108.],
[ 50.,  90.,  97.]])
``````

If dimention of matrix is not according to the rul then you can not perform matrix multipication

``````# example with error
m1@m2
``````
``````---------------------------------------------------------------------------

RuntimeError                              Traceback (most recent call last)

<ipython-input-29-f3553d88c578> in <module>
1 # example with error
----> 2 m1@m2

RuntimeError: size mismatch, m1: [3 x 2], m2: [3 x 2] at /opt/conda/conda-bld/pytorch_1587428266983/work/aten/src/TH/generic/THTensorMath.cpp:41
``````
``````m1.shape
``````
``````torch.Size([3, 2])
``````
``````m2.shape
``````
``````torch.Size([3, 2])
``````

The dimension of m1 is 3x2 and the dimension of m2 is 3x2 so m1 column is not matched with m2 rows 3!=2 that's why this is fire dimension error