NumPy Element Wise Multiplication

The NumPy multiply() function can be used to compute the element-wise multiplication of two arrays with the same shape, as well as multiply an array with a single numeric value. This function provides several parameters that allow the user to specify what value to multiply with. When used with two arrays of the same shape, numpy.multiply() performs element-wise multiplication, meaning it multiplies the corresponding elements of the input arrays to produce an output array with the same shape.

Use numpy.multiply() function to multiplicate the first array elements (arr) with the second array elements (arr1). In this article, I will explain how to use the NumPy multiply() function and using it to returns an array that contains the multiplication of an input array.  

1. Quick Examples of Element Wise Multiplication

If you are in a hurry, below are some quick examples of how to use NumPy element-wise multiplication.

# Quick examples of element wise multiplication

# Example 1: Using multiply() function
# Get multiplication values 
arr = [2, 4, 6, 8, 5, 7] 
arr2 = np.multiply(arr,3)

# Example 2: Use numpy.multiply() function 
# To multiplication two numbers  
arr = 5
arr1 = 8  
arr2 = np.multiply(arr, arr1) 

# Example 3: Use numpy.multiply() function
arr2 = np.multiply(3, 9)

# Example 4: Use numpy.multiply() 
# Get the multiplication 
arr = np.array([2, 4, 6, 8, 1])
arr1 =np.array( [3, 5, 7, 9, 2])
arr2 = np.multiply(arr, arr1)

# Example 5: Use numpy.mutiply() function 
# Get the matrix multiplication
arr = np.array([[2, 4, 6, 8],[1, 3, 5, 7]])
arr1 = np.array([[2, 3, 5, 4],[8, 5, 3, 2]])
arr2 = np.multiply(arr, arr1)

# Example 6: Get the certain rows multiplication
arr2 = np.multiply(arr[1,:],arr1[0,:])
arr3 = np.multiply(arr[ 0,: 2], arr1[ 1,: 1])
arr4 = np.multiply(arr[ 1,: 3], arr1[ 0,: 1])

# Example 7: Using the * operator
# Element-wise multiplication 
arr = np.array([[2, 4, 6, 8],[7, 3, 5, 9]])
arr1 = np.array([[3, 7, 5, 4],[8, 6, 9, 2]])
arr2 = arr * arr1

2. Syntax of multiply()

Following is the syntax of numpy.multiply() function.

# Syntax of numpy.multiply() 
numpy.multiply(arr, arr1, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = 

2.1 Parameters of NumPy multiply()

Following are the parameters of multiply().

• arr – The first input array or object works as a multiplication.
• arr1 – Second input array or object which works as a multiplication.
• out – It is ndarray, None, or tuple of ndarray and None, optional. Out will be the location where the result is to be stored. If provided, it must have a shape that the inputs broadcast to. If not provided or None, a freshly allocated array is returned.
• where (optional) – This parameter is used to specify conditions for element-wise multiplication. If where is True (default), perform the operation. If False, skip the operation and return the input array.
• casting (optional) – Controls what kind of data casting may occur during the operation. Default is ‘same_kind’.
• order – {‘C’, ‘F’, ‘A’, ‘K’}, optional: ‘C’: means to flatten in row-major using C-style order. ‘F’: means to flatten in column-major (Fortran- style) order. ‘A’: means to flatten in column-major order if a is Fortran contiguous in memory, row-major order otherwise. K’: means to flatten an in the order the elements occur in memory. By default, the ‘C’ index order is used.
• dtype – It is an optional parameter that specifies the data type of the returned array.

2.2 Return value

It returns an array that contains the multiplication values of input arrays.

3. Usage of NumPy multiply() Function

The numpy.multiply() is a mathematical function and is used to calculate the multiplication between two NumPy arrays. Returns a multiplication of the inputs, element-wise.

You can multiply the array with a scalar value, to do so, you have taken an array named arr as a multiplicated and the scalar value 3 which indicates the multiplication. Now you will pass the array and scalar value as an argument in numpy.multiply() function. First, you have to create an NumPy array and then, apply this function.

# Import numpy
import numpy as np

# Creating an 1D input array
arr = [2, 4, 6, 8, 5, 7] 
print("Original array:\n",arr)

# Using multiply() function
# Get multiplication values 
arr2 = np.multiply(arr,3)
print("After element-wise multiplication:\n",arr2)

Yields below output.

4. Use numpy.multiply() Function To Multiplication Two Numbers

The numpy.multiply() function in NumPy is typically used for element-wise multiplication of arrays. If you want to multiply two scalar numbers, you can simply use the * operator in Python.

In the below example, the * operator is used to multiply arr and arr1 directly, resulting in the product 40. The numpy.multiply() function is not necessary for multiplying two scalar numbers, it is more suitable for element-wise multiplication of arrays.

import numpy as np

# Initialize variables
arr = 5
arr1 = 8

# Using the * operator 
# To multiply two numbers
arr2 = arr * arr1
print("After multiplying two numbers:\n",arr2)

# Use numpy.multiply() function 
# To multiplication two numbers    
arr2 = np.multiply(arr, arr1)  
print("After multiplying two numbers:\n",arr2)

Yields below output.

You can use numpy.multiply() function to multiply two scalar numbers as well. For example, you are using the numpy.multiply() function to multiply 3 and 9, and the result will be stored in the variable arr2. In this code, the numpy.multiply() function multiplies 3 and 9, and the output is 27.

# Use numpy.multiply() function
arr2 = np.multiply(3, 9)
print("After multiplying two numbers:\n",arr2)

# Output:
After multiplying two numbers:
 27

5. Multiplication NumPy Array Elementwise

Alternatively, you have created two NumPy arrays arr and arr1, and then used the numpy.multiply() function to perform element-wise multiplication between these two arrays. In this code, numpy.multiply() performs element-wise multiplication between arr and arr1, resulting in the array [6, 20, 42, 72, 2].

import numpy as np

# Creating two input array
arr = np.array([2, 4, 6, 8, 1])
arr1 =np.array( [3, 5, 7, 9, 2])

# Use numpy.multiply() 
# Get the multiplication 
arr2 = np.multiply(arr, arr1)
print("After element-wise multiplication:\n",arr2)

# Output:
# After element-wise multiplication:
#  [ 6 20 42 72  2]

7. Use NumPy.multiply() with Two Dimension Arrays

You can use the numpy.multiply() function to perform element-wise multiplication with two-dimensional arrays. For instance, numpy.multiply() performs element-wise multiplication on the two 2D arrays arr and arr1, resulting in the output array [[ 4 12 30 32], [ 8 15 15 14]]. Each element in the output array is calculated by multiplying the corresponding elements from the input arrays.

import numpy as np

# Create a numpy two dimensional arrays
arr = np.array([[2, 4, 6, 8],[1, 3, 5, 7]])
arr1 = np.array([[2, 3, 5, 4],[8, 5, 3, 2]])

# Use numpy.mutiply() function
# Get the matrix multiplication
arr2 = np.multiply(arr, arr1)
print("After element-wise multiplication:\n",arr2)

# Output:
# After element-wise multiplication:
#  [[ 4 12 30 32]
#  [ 8 15 15 14]]

To pass certain rows, columns, or submatrices to the numpy.multiply() function and get the multiplication of certain rows, columns, and submatrices. You should follow the same sizes of the rows, columns, or submatrices that you pass as our operands. Let’s take an example,

# Get the certain rows multiplication
arr2 = np.multiply(arr[1,:],arr1[0,:])
print(arr2)

# Output:
# [ 2  9 25 28]

arr3 = np.multiply(arr[ 0,: 2], arr1[ 1,: 1])
print(arr3)

# Output:
# [16 32]

arr4 = np.multiply(arr[ 1,: 3], arr1[ 0,: 1])
print(arr4)

# Output:
# [ 2  6 10]

8. Multiplication NumPy Arrays With the * Operator

You can multiply NumPy arrays element-wise using the * operator. When you use the * operator between two NumPy arrays, it performs element-wise multiplication.

In the below example, the * operator performs element-wise multiplication on the two 2D arrays arr and arr1, resulting in the output array [[ 6 28 30 32], [56 18 45 18]]. Each element in the output array is calculated by multiplying the corresponding elements from the input arrays.

import numpy as np

# Create a numpy two dimensional arrays
arr = np.array([[2, 4, 6, 8],[7, 3, 5, 9]])
arr1 = np.array([[3, 7, 5, 4],[8, 6, 9, 2]])

# Using the * operator
# Element-wise multiplication 
arr2 = arr * arr1
print("After element-wise multiplication:\n",arr2)

# Output:
# After element-wise multiplication:
#  [[ 6 28 30 32]
#  [56 18 45 18]]

Frequently Asked Questions

Conclusion

In this article, I have explained how to use numpy.multiply() function that performs element-wise multiplication between two arrays in NumPy. It can be used to multiply 1-D arrays, 2-D arrays, or even multi-dimensional arrays. When using numpy.multiply(), ensure that the input arrays have compatible shapes according to NumPy’s broadcasting rules.

Happy Learning!!

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References

• https://numpy.org/doc/stable/reference/generated/numpy.multiply.html