What is the difference between eigenvalues and eigenvectors? (original) (raw)
Last Updated : 23 Jul, 2025
Eigenvalues and eigenvectors are concepts that are used in Linear Algebra which is an important branch of Mathematics and which serves as the basis of many areas of Physics, Engineering and even Computer Science. The eigenvector of the matrix is the non-zero vector which either extends or reduces only using scalar factor while being operated by that matrix. The corresponding eigenvalue is the scalar which is used for describing how the eigenvector is changed, that is, scaled, during this transformation. Both form a toolkit about linear transformations as linear operators and their properties and behaviour which are crucial for deepening understanding of complex properties of a given system and solving diverse differential equations. This introduction lays the foundation on which to discuss the mathematical specifics of eigenvalues and eigenvectors as well as highlight their uses.
What is eigenvalues
Eigenvalues are the numerical values that are related to the eigenvectors in linear transform. The term Eigen is a word borrowed from the German language and is used in mathematics and is derived from the German word Eigen meaning characteristic. Therefore, these are eigenvalues, which express the amount by which eigenvectors are expanded in the direction of the eigenvector. It does not presuppose the alteration of the orientation of the vector apart from instances where the eigenvalue is negative. When the Eigenvalue is negative it’s just reversed in direction. The equation for eigenvalue is given
Av = λv
Where,
- A is the matrix,
- v is associated eigenvector, and
- λ is scalar eigenvalue.
What is eigenvectors
Eigenvectors for square matrices are defined as non-zero vector values such that when the vectors are multiplied by the square matrices, the resultant matrix is the scaler multiple of the vector that is, we define an eigenvector for matrix A as “v” that satisfies the following condition Av = λv
The scaler multiple λ in the above case is known as the eigenvalue of the above-being square matrix. In almost every case, we are first required to find the eigenvalues of the square matrix before we look for the eigenvectors of the matrix.
Eigenvector Equation
The Eigenvector equation is the equation that is used to find the eigenvector of any square matrix. The eigenvector equation is,
Av = λv
Where,
- A is the given square matrix,
- v is the eigenvector of matrix A, and
- λ is any scaler multiple.
Difference between eigenvalues and eigenvectors
| Parameters | Eigenvalues | Eigenvectors |
|---|---|---|
| Definition | Scalars indicating how a transformation scales | Vectors indicating the direction of scaling |
| Mathematical Representation | λ | v |
| Existence | Eigenvalues exist for every matrix | Eigenvectors exist only for non-zero eigenvalues |
| Uniqueness | There can be multiple eigenvalues, some may be repeated | Corresponding eigenvectors can form a subspace |
| Dependence on Matrix | Directly derived from the characteristic polynomial | Derived from solving (A-xI)v = 0 |
| Type | Always scalars | Always vectors |
| Geometric Interpretation | Represents scaling factor | Represents direction vector |
| Dimensionality | Single dimension (scalar) | Same dimension as the original matrix (vector) |
| Physical Interpretation | Can represent frequencies, energy levels, etc. | Can represent vibration modes, principal directions |
| Complexity | Generally simpler to compute | Involves solving linear equations |
| Symmetry in Real Matrices | Eigenvalues are real for symmetric matrices | Eigenvectors are orthogonal for symmetric matrices |
Applications of Eigenvalues
- **Stability Analysis in Dynamical Systems: Eigenvalues are used to determine the stability of equilibrium points in different dynamic systems. The eigenvalues of the Jacobian matrix of the system at an equilibrium point are all negative in real parts, the equilibrium is stable The eigenvalues of the Jacobian matrix of the system with positive real parts the equilibrium is unstable.
- **Quantum Mechanics: In quantum mechanics, eigenvalues are states of a physical system that correspond to a particular value of an operator, for example, the energy of an electron in an atom. For example, the Schrödinger equation involves searching for eigenvalues of the Hamilton operators which are equivalent to the energies of the system.
- **Vibration Analysis: Eigenvalues are employed in the estimation of the natural frequency of vibration of a mechanical structure. Natural frequencies that are quite important in attempting to counter-check any cases of resonance in structures come from the eigenvalues of the system mass and stiffness matrices.
- **Principal Component Analysis (PCA): PCA is a method that is implemented under the category of exploratory factor analysis, as a method of the reduction of variables. From the covariance matrix, the eigenvalues that define the principal components tell us the proportion of variance explained by each of the new variables. The larger eigenvalues represent features with more spread-out values in the dataset.
- **Markov Chains: In Markov chains, the measure of the distances between states is expressed via the eigenvalues of the Transition Probability matrix to describe the long-term behaviour of the dynamical system. The first eigenvalue can be the largest in the case of a stochastic matrix with the value often being 1 and others are about how fast it will converge.
Applications of Eigenvectors
- **Principal Component Analysis (PCA): Since eigenvectors of the covariance matrix can be viewed as directions of maximum variability, they are called also principal components. Eigenvectors above are used to map the originally used matrices into a new Fourier space of lower Dimensionality.
- **Molecular Orbital Theory: Eigenvectors of the Hamiltonian matrix in the molecular orbital theory of chemistry provide the molecular orbitals. The eigenvalues are the same as the energy levels of such orbitals, while the eigenvectors define the spatial configuration of the orbitals.
- **Google PageRank Algorithm: Google uses a method called PageRank to sort the Web pages and it is defined by the eigenvector of the Web page graph’s adjacency matrix. The principal eigenvector is a contour of the random surfers’ long-term behaviour to give the importance of each of the pages.
- **Image Compression: Compression techniques involving the use of Singular Value Decomposition (SVD) work by using eigenvectors of the image matrix to reconstruct the image with lower data. The eigenfeatures equal to the largest eigenvalues contain features of an image that can be important during the determination of likeness.
- **Mechanical Vibrations and Mode Shapes: In Structural dynamics, eigenvectors are used as the mode shapes of a vibrating system. These mode shapes characterise the vibration pattern or distortion of the structure at each natural frequency, which is key data in the design and analysis of structures influenced by the dynamic load.
Conclusion
In conclusion, eigenvalues and eigenvectors are core topics in linear algebra that help to comprehend linear transformations and their impact on vector spaces. Therefore, eigenvalues as scalars measure the extent of this scaling while eigenvectors as vectors identify the direction of this scaling. Its use covers areas of stability analysis, quantum mechanics, vibration analysis and also data reduction techniques such as the principal component analysis. Their long-standing descriptions enhance the knowledge of their behaviour in the systems and matrices that we come across.