# NumPy Dot Product – numpy.dot()

Contents

## NumPy Dot Product

To compute dot product of numpy nd arrays, you can use numpy.dot() function.

numpy.dot() function accepts two numpy arrays as arguments, computes their dot product, and returns the result.

## Syntax

The syntax of numpy.dot() function is

``numpy.dot(a, b, out=None)``

## Behavior of numpy.dot() based on Input Array Dimensions

The following table specifies the type of operation done based on the dimensions of input arrays: a and b.

## Examples

### 1. Dot Product of Scalars

In this example, we take two scalars and calculate their dot product using numpy.dot() function. Dot product using numpy.dot() with two scalars as arguments return multiplication of the two scalars.

Python Program

``````import numpy as np

a = 3
b = 4
output = np.dot(a,b)
print(output)``````
Run Code Copy

Output

``12``

Explanation

``````output = a * b
= 3 * 4
= 12``````

### 2. Dot Product of 1D Arrays (Vectors)

In this example, we take two numpy one-dimensional arrays and calculate their dot product using numpy.dot() function. We already know that, if input arguments to dot() method are one-dimensional, then the output would be inner product of these two vectors (since these are 1D arrays).

Python Program

``````import numpy as np

# Initialize arrays
A = np.array([2, 1, 5, 4])
B = np.array([3, 4, 7, 8])

# Dot product
output = np.dot(A, B)

print(output)``````
Run Code Copy

Output

``77``

Dot Product

``````output = [2, 1, 5, 4].[3, 4, 7, 8]
= 2*3 + 1*4 + 5*7 + 4*8
= 77``````

### 3. Dot Product of 2-D Arrays (Matrix)

In this example, we take two two-dimensional numpy arrays and calculate their dot product. Dot product of two 2-D arrays returns matrix multiplication of the two input arrays.

Python Program

``````import numpy as np

# Initialize arrays
A = np.array([[2, 1], [5, 4]])
B = np.array([[3, 4], [7, 8]])

# Dot product
output = np.dot(A, B)

print(output)``````
Run Code Copy

Output

``````[[13 16]
[43 52]]``````

Dot Product

``````output = [[2, 1], [5, 4]].[[3, 4], [7, 8]]
= [[2*3+1*7, 2*4+1*8], [5*3+4*7, 5*4+4*8]]
= [[13, 16], [43, 52]]``````

## Summary

In this NumPy Tutorial, we learned how to calculate the dot product of numpy arrays, with the help of well detailed example programs.

## Related Tutorials

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