# What Is Eigenvalue and Eigenvector in Linear Algebra?

April 26, 2023 Janet Kim
United States
Algebra
Dr. Kim has worked as an associate professor in the mathematics Department of a prestigious university in the united states. She has supervised multiple Ph.D. students in these fields and has taught a variety of courses on linear algebra, matrix theory, and numerical analysis at both the undergraduate and graduate levels.

Mathematicians who specialize in linear algebra must be acquainted with linear equations and their solutions. Linear algebra is a crucial tool in contemporary computer science, engineering, and mathematics. The idea of eigenvalues and eigenvectors is among the most crucial ones in linear algebra. Fundamental ideas in linear algebra known as eigenvalues and eigenvectors have several uses in the fields of physics, engineering, and computer science.

Systems of differential equations, matrices, and linear transformations are all studied using eigenvalues and eigenvectors. Additionally, they are employed in pattern recognition, image processing, and data analysis. In-depth explanations of the eigenvalue and eigenvector concepts, as well as an examination of how they are used in various fields, are covered in this article.

## What is an Eigenvalue?

Eigenvalue Is a scalar that denotes the strength of a transformation in a specific direction. A vector's eigenvalue, in other words, is a measurement of how much a transformation stretches or compresses it. Eigenvalues are crucial because they give insight into how a transformation modifies a vector's size and shape.

We first need to comprehend linear transformations to understand eigenvalues. A linear transformation is a function that maintains the linear structure of the vector space while mapping one vector to another. A rotation of a vector in a plane, for instance, is an example of a linear transformation because it keeps the vector's length and direction.

Now, let be a scalar and T be a linear transformation on a vector space V. If there is a non-zero vector x in the set V such that T(x) = x, then x is referred to as an eigenvector of T corresponding to x and is referred to as an eigenvalue of T.

In other words, a scalar such that T(x) = x for some non-zero vector x is an eigenvalue of a linear transformation T. An eigenvector of T that corresponds to x is referred to as the vector. Remember that the identity transformation, I, can be used to write the equation T(x) = x as (T - I)x = 0. This indicates that the eigenvector x is a non-zero vector that is located in the transformation T - I's null space.

## What is An Eigenvector?

A non-zero vector that has undergone solely a transformation's scaling is an eigenvector. Eigenvectors are crucial because they offer a means of comprehending how a transformation modifies a vector's direction. A vector that maintains its direction after a linear transformation is said to be an eigenvector.

Let's consider the transformation of a vector by a matrix to comprehend eigenvectors. When representing a linear transformation, a matrix is a rectangular array of numbers. For instance, a 2x2 matrix can be used to describe the rotation of a vector in the plane.

Now, assume that A is a square matrix and that is one of A's eigenvalues. A non-zero vector x that satisfies the equation Ax = x is an eigenvector of A and corresponds to the symbol.

To put it another way, an eigenvector of a matrix A is a non-zero vector x that, when A is applied to it, produces a vector that is parallel to x. The scalar factor is the factor by which the length of x is multiplied.

It's significant to remember that not every matrix has eigenvectors. If and only if the determinant of A - I, where I is the identity matrix, equals zero, a matrix A possesses eigenvectors.

Applications Of Eigenvalue and Eigenvector

There are several uses for eigenvalues and eigenvectors in many different domains. Some of the most typical applications are listed below:

### Image Processing

Fundamental ideas in quantum mechanics, the area of physics that examines the behavior of matter and energy at the atomic and subatomic scales, include eigenvalues and eigenvectors. The invention of transistors, lasers, and MRI machines are just a few examples of the significant technological advancements made possible by the very successful theory of quantum mechanics.

In quantum physics, wave functions—mathematical functions that depict the likelihood of locating a physical system in a specific state—are used to characterize the properties of physical systems. The Schrödinger equation, a partial differential equation that defines how the wave function evolves, governs the time evolution of the system. Wave functions are commonly represented as vectors in a complex vector space.

In quantum physics, the eigenvalues and eigenvectors of the Hamiltonian operator, which symbolize the overall energy of the system, are very significant. The corresponding states of the system are represented by the eigenvectors, while the permitted energies of the system are represented by the eigenvalues of the Hamiltonian operator.

Because they do not vary over time, the eigenstates of the Hamiltonian operator in particular are referred to as "stationary states." The square of the absolute value of the appropriate eigenvector component, when a quantum system is in a stationary state, indicates the likelihood of finding the system in a specific energy level.

In quantum physics, eigenvalues and eigenvectors are crucial for measuring physical observables. Hermitian operators, which have actual eigenvalues and orthogonal eigenvectors, are used to represent physical observables like location, momentum, and spin.

The wave function of the system collapses into one of the relevant operator's eigenstates when a physical observable is measured, with a probability determined by the square of the absolute value of the corresponding eigenvector component. The eigenvalue of the pertinent eigenstate serves to represent the measurement's outcome.

The study of quantum entanglement, a phenomenon in which two or more quantum systems become coupled in a way that prevents their wave functions from being described independently of one another, also makes use of eigenvalues and eigenvectors. By calculating the eigenvalues and eigenvectors of the related density matrix, which reflects the probability distribution of the entangled states, the entanglement between the two systems can be measured.

### Quantum Mechanics

Fundamental ideas in quantum mechanics, the area of physics that examines the behavior of matter and energy at the atomic and subatomic scales, include eigenvalues and eigenvectors. The invention of transistors, lasers, and MRI machines are just a few examples of the significant technological advancements made possible by the very successful theory of quantum mechanics.

In quantum physics, wave functions—mathematical functions that depict the likelihood of locating a physical system in a specific state—are used to characterize the properties of physical systems. The Schrödinger equation, a partial differential equation that defines how the wave function evolves, governs the time evolution of the system. Wave functions are commonly represented as vectors in a complex vector space.

In quantum physics, the eigenvalues and eigenvectors of the Hamiltonian operator, which symbolize the overall energy of the system, are very significant. The eigenvalues of the Hamiltonian operator represent the permitted energies of the system, while the eigenvectors represent the corresponding states of the system.

Because they do not vary over time, the eigenstates of the Hamiltonian operator in particular are referred to as stationary states. The square of the absolute value of the appropriate eigenvector component, when a quantum system is in a stationary state, indicates the likelihood of finding the system in a specific energy level.

In quantum physics, eigenvalues and eigenvectors are crucial for measuring physical observables. Hermitian operators, which have actual eigenvalues and orthogonal eigenvectors, are used to represent physical observables like location, momentum, and spin.

### Control Theory

In control theory, which is the study of mathematical models of dynamic systems and the creation of controllers to regulate their behavior, eigenvalues, and eigenvectors are crucial tools. Applications of control theory include industrial automation, robotics, and the control of airplanes and spacecraft.

The analysis of a dynamic system's stability and performance is one of the main uses of eigenvalues and eigenvectors in control theory. A collection of differential equations that describe how a system's state changes over time can be used to depict a dynamic system. By linearizing the differential equations around an equilibrium point, the system matrix's eigenvalues allow for the evaluation of the system's stability.

Specifically, if all of the system matrix's eigenvalues have negative real portions, the system is considered to be stable and will, after being perturbed, revert to its equilibrium state. The system is said to be unstable if any of the eigenvalues have positive real components, meaning that after being perturbed, it will diverge from its equilibrium state.

The system's performance can also be examined using the eigenvectors of the system matrix. The dominant eigenvector, which shows the direction of maximal growth or decay in the system, is specifically known as the eigenvector corresponding to the largest eigenvalue. It is possible to enhance the system's performance by changing the dominant eigenvector by altering the system matrix.

The design of control systems—devices or algorithms that alter a system's inputs to produce a desired output—also makes use of eigenvalues and eigenvectors. The process of choosing the desired eigenvalues of the system matrix and creating a controller that will attain those eigenvalues is known as eigenvalue assignment, and it is a popular technique for developing control systems.

### Machine Learning

In machine learning, which is the study of statistical models and algorithms that allow computers to learn from data without being explicitly programmed, eigenvalues and eigenvectors are also frequently utilized. Eigenvalues and eigenvectors in machine learning techniques offer effective and powerful methods for manipulating and analyzing huge matrices.

In machine learning, the analysis of covariance matrices is one application where eigenvalues and eigenvectors are frequently used. Covariance matrices, which are frequently big and dense, are used to express the correlations between several variables in a dataset. The primary components of the dataset—the directions in which the data fluctuates most—can be found by computing the eigenvalues and eigenvectors of the covariance matrix.

Dimensionality reduction, a method for reducing the number of variables in a dataset while preserving the majority of the information, can be carried out using the main components. This is especially helpful for high-dimensional datasets where there may be many more variables than samples. We can decrease the dataset's dimensionality while still keeping the most crucial information by projecting the data onto the major components.

Several other machine learning algorithms, including matrix factorization, principal component analysis, and singular value decomposition, also employ eigenvalues and eigenvectors. These algorithms are used to identify patterns and correlations between the variables as well as to extract key elements from the data.

Additionally, eigenvalues and eigenvectors are employed in deep learning, a branch of machine learning that employs neural networks. Neural networks are computer models that are used for functions including speech recognition, natural language processing, and picture recognition. They are modeled after the structure and operation of the human brain.

### Graph Theory

The study of networks and graphs is the focus of the branch of mathematics known as graph theory. A graph is made up of vertices, also known as nodes, and edges, also known as linkages. In graph theory, eigenvalues and eigenvectors are crucial tools for examining the characteristics and behavior of graphs and networks.

The examination of a graph's adjacency matrix is one of the main uses of eigenvalues and eigenvectors in graph theory. A graph's adjacency matrix is a matrix that details the relationships between the graph's vertices. The (i,j)-entry of the matrix, in particular, is equal to 1 if an edge connects vertices i and j and 0 otherwise.

The connectivity of the graph can be described using the eigenvalues of the adjacency matrix. The diameter of the graph, or the longest shortest path between any two vertices, is connected to the biggest eigenvalue of the adjacency matrix, which is known as the spectral radius of the graph. The most significant or core nodes in the network can also be determined using the eigenvector that corresponds to the biggest eigenvalue.

It is possible to examine additional aspects of graphs, such as their symmetry and structure, using eigenvalues and eigenvectors. A symmetric matrix, such as the adjacency matrix of a symmetric graph, denotes that all of its eigenvalues are real and all of its eigenvectors are orthogonal. The number of distinctive eigenvalues in the adjacency matrix also tells us how many graph elements are related to one another.

The study of random walks on graphs also makes use of eigenvalues and eigenvectors. The probability that a particle will go to a specific vertex depends on the connections between the vertices as it moves randomly from one vertex to the next during a random walk. The eigenvalues of the adjacency matrix can be used to calculate the rate of convergence to the stationary distribution, and they can also be used to calculate the stationary distribution of the random walk.

## Conclusion

Fundamental ideas in linear algebra, eigenvalues, and eigenvectors have numerous applications in numerous disciplines. While eigenvectors reflect the direction of a vector that has merely undergone a scaling transformation, eigenvalues represent the magnitude of a linear transformation along a certain direction. The properties and behavior of linear systems, matrices, and differential equations, as well as in image processing, quantum physics, control theory, machine learning, and graph theory, can all be studied using eigenvalues and eigenvectors.