# Return the Lower triangle of an array in Numpy

To return the lower triangle of an array, use the numpy.tril() method in Python Numpy. The 1st parameter is the input array. The function returns a copy of an array with elements above the k-th diagonal zeroed. For arrays with ndim exceeding 2, tril will apply to the final two axes.

The k is the diagonal above which to zero elements. k = 0 (the default) is the main diagonal, k < 0 is below it and k > 0 is above.

## Steps

At first, import the required library −

import numpy as np

Create a 2d array −

arr = np.array([[36, 36, 78, 88], [92, 81, 98, 45], [22, 67, 54, 69 ], [69, 80, 80, 99]])


Display the array −

print("Array...",arr)

Get the datatype −

print("Array datatype...",arr.dtype)


Get the dimensions of the Array −

print("Array Dimensions...",arr.ndim)

Get the shape of the array −

print("Our Array Shape...",arr.shape)


Get the number of elements of the Array −

print("Elements in the Array...",arr.size)

To return the lower triangle of an array, use the numpy.tril() method. The 1st parameter is the input array −

print("Result...",np.tril(arr))


## Example

import numpy as np

# Create a 2d array
arr = np.array([[36, 36, 78, 88], [92, 81, 98, 45], [22, 67, 54, 69 ], [69, 80, 80, 99]])

# Displaying our array
print("Array...",arr)

# Get the datatype
print("Array datatype...",arr.dtype)

# Get the dimensions of the Array
print("Array Dimensions...",arr.ndim)

# Get the shape of the Array
print("Our Array Shape...",arr.shape)

# Get the number of elements of the Array
print("Elements in the Array...",arr.size)

# To return the lower triangle of an array, use the numpy.tril() method in Python Numpy
# The 1st parameter is the input array
print("Result...",np.tril(arr))

## Output

Array...
[[36 36 78 88]
[92 81 98 45]
[22 67 54 69]
[69 80 80 99]]

Array datatype...
int64

Array Dimensions...
2

Our Array Shape...
(4, 4)

Elements in the Array...
16

Result...
[[36 0 0 0]
[92 81 0 0]
[22 67 54 0]
[69 80 80 99]]

Updated on: 10-Feb-2022

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