Understanding numpy.log() in Python

Filed Under: Python Modules
Numpylog

In this tutorial, we will learn about the numpy.log() in Python. The Numpy module offers powerful data manipulation methods. It mostly deals with data stored in arrays.

The Numpy.log() method lets you calculate the mathematical log of any number or array.

Let’s learn how to use numpy.log() to calculate log in python.

Using numpy.log() in Python

To use numpy.log() we will first have to import the Numpy module.

import numpy

Now we can use numpy.log() to find out the log of different numbers.

import numpy as np
print(np.log(10))

Output:

2.302585092994046

Let’s try another example.

import numpy as np 
print(np.log(np.e))

Output :

1.0

We get 1 as the output as numpy.log by default calculates the natural log. The natural log is calculated with a base of e. The value of e is :

 2.718281828459

Let’s try calculating the log of 0.

Using numpy.log() on 0

Let’s see what happens when we use the numpy.log function on 0.

import numpy as np 
print(np.log(0))

Output:

-inf 
/usr/local/lib/python3.6/dist-packages/ipykernel_launcher.py:1: RuntimeWarning: divide by zero encountered in log

The logarithm of zero is not defined. It’s not a real number, because you can never get zero by raising anything to the power of anything else.

There are some other logs that you can calculate using np.log. These are log2 and log10 which are logarithms with base 2 and 10 respectively.

1. Calculating log with base 2

To calculate logarithm with base 2, use log2 in place of log.

import numpy as np 
print(np.log2(8))

Output:

3.0

Let’s try another example.

import numpy as np 
print(np.log2(32))

Output:

5.0

2. Calculating log with base 10

To calculate logarithm with base 10, use log10 in place of log.

import numpy as np 
print(np.log10(100))

Output :

2.0

Let’s try another example.

import numpy as np
print(np.log10(10000))

Output :

4.0

Using Numpy.log() on Arrays

Let’s see how to use numpy.log on arrays.

1. Calculating Logarithm of a 1D array

To calculate the logarithm of a 1D array use :

import numpy as np 
arr = np.array([1,2,4,5,6,8])
print(np.log2(arr))

Output:

[0. 1. 2. 2.32192809 2.5849625 3.]

2. Calculating Logarithm of a 2D array

To calculate the logarithm of a 2D array use :

import numpy as np 
arr_2d = np.arange(4,10).reshape((2,3))
print(arr_2d)
print(np.log2(arr_2d))

Output :

[[4 5 6]
 [7 8 9]]
[[2.         2.32192809 2.5849625 ]
 [2.80735492 3.         3.169925  ]]

Plotting numpy.log() function using Matplotlib

Let’s try plotting a graph for the logarithmic function. To plot a graph we will need a lot of points in our array. Our approach is as follows :

We will create a Numpy array of integers from 1 to 1000. Then we will store the log of this array. Finally, we will create a plot using the stored values.

Let’s see the code for the same.

import numpy as np
import matplotlib.pyplot as plt

arr = np.arange(start = 1, stop = 1000)

log_val=np.log(arr)

plt.plot(log_val,arr,color='purple')

Output :

numpy.Log in Python
Log

Conclusion

This tutorial was about the Numpy.log function in Python. We learn how to use numpy.log for calculating logs of integers and arrays. We also learned how to plot a graph using numpy.log and matplotlib.

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