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# Create a two-dimensional array with the flattened input as lower diagonal in Numpy

To create a two-dimensional array with the flattened input as a diagonal, use the **numpy.diagflat()** method in Python Numpy. The 'K parameter is used to set the diagonal; 0, the default, corresponds to the “main” diagonal, a negative k giving the number of the diagonal below the main.

The first parameter is the input data, which is flattened and set as the k-th diagonal of the output. The second parameter is the diagonal to set; 0, the default, corresponds to the “main” diagonal, a positive (negative) k giving the number of the diagonal above (below) the main.

NumPy offers comprehensive mathematical functions, random number generators, linear algebra routines, Fourier transforms, and more. It supports a wide range of hardware and computing platforms, and plays well with distributed, GPU, and sparse array libraries.

## Steps

At first, import the required library −

import numpy as np

Create a 2D array using the numpy.array() method −

arr = np.array([[5, 10], [15, 20]])

Displaying our array −

print("Array...\n",arr)

Get the datatype −

print("\nArray datatype...\n",arr.dtype)

Get the dimensions of the Array −

print("\nArray Dimensions...\n",arr.ndim)

Get the shape of the Array −

print("\nOur Array Shape...\n",arr.shape)

Get the number of elements of the Array −

print("\nElements in the Array...\n",arr.size)

Now, create a two-dimensional array with the flattened input as a diagonal using the numpy.diagflat() method. The 'K parameter is used to set the diagonal; 0, the default, corresponds to the “main” diagonal, a negative k giving the number of the diagonal below the main −

print("\nResult...\n",np.diagflat(arr, k = -1))

## Example

import numpy as np # Create a 2D array using the numpy.array() method arr = np.array([[5, 10], [15, 20]]) # Displaying our array print("Array...\n",arr) # Get the datatype print("\nArray datatype...\n",arr.dtype) # Get the dimensions of the Array print("\nArray Dimensions...\n",arr.ndim) # Get the shape of the Array print("\nOur Array Shape...\n",arr.shape) # Get the number of elements of the Array print("\nElements in the Array...\n",arr.size) # To create a two-dimensional array with the flattened input as a diagonal, use the numpy.diagflat() method in Python Numpy print("\nResult...\n",np.diagflat(arr, k = -1))

## Output

Array... [[ 5 10] [15 20]] Array datatype... int64 Array Dimensions... 2 Our Array Shape... (2, 2) Elements in the Array... 4 Result... [[ 0 0 0 0 0] [ 5 0 0 0 0] [ 0 10 0 0 0] [ 0 0 15 0 0] [ 0 0 0 20 0]]

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