# Mastering the Cross Product of Two Vectors in Python

## Cross Product of Two Vectors in Python – A Comprehensive Guide

When working with vectors, one of the most useful operations that we come across is the cross product. The cross product of two vectors is a vector that is orthogonal (perpendicular) to both the input vectors.

It is often used in physics, mathematics, and computer graphics for applications such as calculating torque and finding surface normals. In this article, we will explore two methods for calculating the cross product of two vectors in Python.

The first method involves using the built-in function cross() from the NumPy library. The second method involves defining our own function.

### Method 1: Using cross() function from NumPy

NumPy is a powerful library in Python that provides support for arrays and matrices. One of the many functions in the NumPy library is cross(), which can be used to calculate the cross product of two vectors.

The syntax for using cross() is simple. It takes two vectors as input and returns their cross product as a new vector.

Here’s an example:

import numpy as np
vector_1 = np.array([1, 2, 3])
vector_2 = np.array([4, 5, 6])
cross_product = np.cross(vector_1, vector_2)

print(cross_product)

### Output:

[-3  6 -3]

In the above example, we created two vectors vector_1 and vector_2. We then passed them as input to the cross() function and stored the output in the variable cross_product.

Finally, we printed the cross product using the print() function.

### Method 2: Defining our own function

Alternatively, we can also define our own function to calculate the cross product of two vectors.

This approach allows us to customize the function according to our needs and have more control over the output. Here’s an example:

def cross_product(vector_1, vector_2):
x = vector_1[1] * vector_2[2] - vector_1[2] * vector_2[1]
y = vector_1[2] * vector_2[0] - vector_1[0] * vector_2[2]
z = vector_1[0] * vector_2[1] - vector_1[1] * vector_2[0]
return [x, y, z]

vector_1 = [1, 2, 3]
vector_2 = [4, 5, 6]
cross_product = cross_product(vector_1, vector_2)

print(cross_product)

### Output:

[-3, 6, -3]

In the above example, we defined a function called cross_product that takes two vectors as input and returns their cross product as a new vector. We then created two vectors vector_1 and vector_2, passed them as input to the cross_product function, and stored the output in the variable cross_product.

Finally, we printed the cross product using the print() function.

## Conclusion

In this article, we learned two methods for calculating the cross product of two vectors in Python. The first method involved using the built-in function cross() from the NumPy library.

The second method involved defining our own function. Both methods are useful and have their own advantages.

By understanding these methods, you can easily calculate the cross product of any two vectors in your Python programs.

### Example 2: Defining our own function

As mentioned earlier, defining our own function to calculate the cross product of two vectors provides us with more control over the output and allows us to customize the function according to our needs.

In this section, we will explore the process of defining our own function to calculate the cross product of two vectors in greater detail. To begin, let us recall the formula to calculate the cross product of two vectors:

A x B = |A||B|sin()n

Here, A and B are the input vectors, |A| and |B| are their magnitudes, is the angle between the vectors, and n is the unit vector orthogonal to both A and B.

We can use this formula to define our own function to calculate the cross product of two vectors in Python. Here’s an example:

import math

def cross_product(vector_1, vector_2):
# Calculate the unit vector
unit_vector = [0, 0, 0]
unit_vector[0] = vector_1[1] * vector_2[2] - vector_1[2] * vector_2[1]
unit_vector[1] = vector_1[2] * vector_2[0] - vector_1[0] * vector_2[2]
unit_vector[2] = vector_1[0] * vector_2[1] - vector_1[1] * vector_2[0]

# Calculate the magnitude of the cross product
magnitude = math.sqrt(unit_vector[0] ** 2 + unit_vector[1] ** 2 + unit_vector[2] ** 2)

# Normalize the unit vector
if magnitude != 0:
unit_vector[0] /= magnitude
unit_vector[1] /= magnitude
unit_vector[2] /= magnitude

return unit_vector

vector_1 = [1, 2, 3]
vector_2 = [4, 5, 6]
cross_product = cross_product(vector_1, vector_2)

print(cross_product)

### Output:

[-0.408248290463863, 0.816496580927726, -0.408248290463863]

In the above example, we defined our own function called cross_product that takes two vectors as input and returns their cross product as a unit vector.

We first defined an empty list called unit_vector that will store the result of the cross product.

We then used the formula mentioned earlier to calculate the unit_vector. Next, we calculated the magnitude of the unit_vector using the math.sqrt() function in Python.

We then normalized the unit_vector by dividing each component by the magnitude. This is done to ensure that the resulting vector has a magnitude of 1.

Finally, we returned the unit_vector as the output of the function.

Some points to note when defining our own function to calculate the cross product:

• The input vectors must be of the same dimension.
• In the above example, we assumed that the input vectors are three-dimensional.
• The order in which the input vectors are passed to the function matters.
• The cross product is anti-commutative, i.e., A x B = -B x A. Hence, changing the order of input vectors will lead to a change in the direction of the resulting vector.
• The output of the function should always be a unit vector. This is because the cross product can only be calculated for vectors in three-dimensional space.
• The cross product is not defined for vectors in two-dimensional space. In this case, we can find the area of the parallelogram formed by the two vectors instead of the cross product.

In summary, defining our own function to calculate the cross product of two vectors in Python provides us with greater control over the output and allows us to customize the function according to our needs. By understanding the formula for the cross product and taking into account the above-mentioned points, we can easily define our own function to calculate the cross product of two vectors in Python.

In conclusion, understanding how to calculate the cross product of two vectors is an essential skill for many applications in physics, mathematics, and computer graphics. Python provides two useful methods for calculating the cross product: using the built-in function cross() from the NumPy library and defining our own function.

While both methods are effective, defining our function provides us with more control and customization options. By understanding the formula for the cross product and considering the key points discussed in the article, we can easily define our own function to calculate the cross product of any two vectors in Python.

Overall, mastering this skill is crucial for anyone looking to work with vectors effectively.