Create Array with Ones Below Main Diagonal in NumPy

To create an array with ones below the main diagonal and zeros elsewhere, use the numpy.tri() method in Python Numpy

• The 1st parameter is the number of rows in the array

• The 2nd parameter is the number of columns in the array

• The 3rd parameter 'k' is the sub-diagonal at and below which the array is filled.

The k = 0 is the main diagonal, while k < 0 is below it, and k > 0 is above. The default is 0. The tri() function returns an array with its lower triangle filled with ones and zero elsewhere; in other words T[i,j] == 1 for j <= i + k, 0 otherwise.

Steps

At first, import the required library −

import numpy as np

Now, create an array with ones below the main diagonal and zeros elsewhere, using the numpy.tri() method −

arr = np.tri(4, 4, k = -1)

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)

Example

import numpy as np

# To create an array with ones below the main diagonal and zeros elsewhere, use the numpy.tri() method in Python Numpy
# The 1st parameter is the number of rows in the array
# The 2nd parameter is the number of columns in the array
# The 3rd parameter 'k' is the sub-diagonal at and below which the array is filled.
# The k = 0 is the main diagonal, while k < 0 is below it, and k > 0 is above. The default is 0.
arr = np.tri(4, 4, k = -1)

# 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)

Output

Array...
[[0. 0. 0. 0.]
[1. 0. 0. 0.]
[1. 1. 0. 0.]
[1. 1. 1. 0.]]

Array datatype...
float64

Array Dimensions...
2

Our Array Shape...
(4, 4)

Elements in the Array...
16