In this tutorial, we will look at how to check if a value in a Numpy array is negative infinity or not with the help of some examples.

## How to test for negative infinity in a Numpy array?

You can use the `numpy.isneginf()`

function to check (element-wise) if values in a Numpy array are negative infinity or not. The following is the syntax –

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# test for negative infinity - pass scaler value or numpy array np.isneginf(a)

It returns a boolean value (`True`

if the value is negative infinity otherwise `False`

) if you pass a scaler value and a boolean array if you pass an array.

## Examples

Let’s now look at some examples of using the above function to test for -ve infinity.

### Example 1 – Check if a number is a negative infinity or not using `numpy.isneginf()`

First, let’s pass scaler values to the `numpy.isneginf()`

function.

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Let’s create three variables – one containing a finite value and the others set to positive and negative infinity respectively and then apply the `numpy.isneginf()`

function on each of these values.

import numpy as np # create three variables with scaler values a = 21 b = np.inf c = -np.inf # check for negative infinity print(np.isneginf(a)) print(np.isneginf(b)) print(np.isneginf(c))

Output:

False False True

We get `True`

as the output for the negative infinity and `False`

as the output for the finite number and the positive infinity.

### Example 2 – Element-wise check for negative infinity in a Numpy array using `numpy.isneginf()`

If you apply the `numpy.isneginf()`

function on an array, it will return a boolean array containing `True`

for values that are negative infinity and `False`

for other values.

Let’s create a 1-D array and apply the `numpy.isneginf()`

function to it.

# create a numpy array ar = np.array([1, 2, np.inf, 4, 5, -np.inf, np.inf]) # check for negative infinity in ar np.isneginf(ar)

Output:

array([False, False, False, False, False, True, False])

We get a boolean array as an output. You can see that in the boolean array we get `True`

for only the values that test as negative infinity in the original array.

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## Summary

In this tutorial, we looked at how we can use the `numpy.isneginf()`

function to check for negative infinity in a Numpy array. Keep in mind that if you pass a scaler value, it returns a boolean value and if you pass a 1-D array it returns a boolean array.

You might also be interested in –

- Numpy – Check If Element is an Infinity (Positive or Negative) or Not
- Numpy – Check for Positive Infinity
- Check If Two Numpy Arrays are Equal

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