# Linear Algebra Basics: Understanding Vectors and Matrices

April 26, 2023 Katie Hartfield
United States
Algebra
Katie is a notable mathematician and a linear algebra specialist. She has mentored many graduate students and researchers in addition to completing their linear algebra assignments. Katie has participated in many outreach initiatives aimed at promoting mathematics education among marginalized populations. She is passionate about passing on her knowledge.

The study of linear equations and their characteristics is known as linear algebra. The study of vectors, matrices, and linear transformations is covered in this area of mathematics. Many disciplines, including physics, engineering, computer science, and economics, require linear algebra. The foundations of linear algebra will be the main topic of this blog, with a focus on understanding vectors and matrices.

## What Are Vectors?

A quantity with both magnitude and direction is represented mathematically by a vector. In linear algebra, a vector is often represented by its components, which are an ordered list of numbers. For instance, the vector [1, 2, 3] denotes a quantity whose magnitude and direction are, respectively, positive x, y, and z axes.

Scalars can multiply, add, and subtract from vectors. By adding the necessary vector components, vector addition is accomplished. For instance, [5, 7, 9] is equal to [1, 2, 3] plus [4, 5, 6]. By subtracting the respective vector components, vector subtraction is accomplished. For instance, [-3, -3, -3] separates [1, 2, 3] from [4, 5, 6]. Each element of the vector is multiplied by a scalar to execute scalar multiplication. For instance, [2, 4, 6] is the result of 2 and [1, 2, 3].

Notation:

Typically, column vectors or row vectors are used to represent vectors in linear algebra. A column of numbers written in brackets designates a vector as a column vector. For instance, a vector with a magnitude of 3 and a direction pointing in the positive x, y, and z directions is represented by the column vector [1, 2, 3]T. By inverting the vector's rows and columns, the transpose of the vector, represented by the letter T, is created.

A row of numbers wrapped in brackets designates a vector as a row vector. For instance, a vector with a magnitude of 3 and a direction pointing in the positive x, y, and z directions is represented by the row vector [1, 2, 3].

The following rules can be used to add and subtract vectors:

1. Add or take away the corresponding vector components. As an illustration, [1, 2, 3] - [4, 5, 6] = [-3, -3, -3] and [1, 2, 3] - [4, 5, 6] = [5, 7, 9].
2. Both the magnitude and the direction of the new vector are identical to the original vectors.

Vector addition is the process of combining the matching elements of two or more vectors to create a new vector. By placing one vector's tail at the head of another vector and drawing a new vector from the first vector's tail to the second vector's head, we can add vectors geometrically. The two vectors' total is represented by this new vector.

For illustration, let's look at two vectors:

u = [3, 2, 1] and v = [1, 2, 3]

The vector represents the sum of u and v:

u + v = [3+1, 2+2, 1+3] = [4, 4, 4]

Vector addition has several significant characteristics, including:

Commutativity: (u + v) + (w + v) = (u + v) + (v + w) Associativity: (u + v) + (w + v)

• Identity: There is a vector 0 such that for all vectors u, u + 0 = u.
• Reverse: There exists a vector -u such that u + (-u) = 0 for any vector u.
• Vector Subtraction

Vector subtraction is the process of removing the corresponding components from two vectors to create a new vector. Geometrically, subtracting two vectors is comparable to drawing a new vector from the tail of the second vector to the head of the first vector by placing the tail of one vector at the head of another vector in the opposite direction. The difference between the two vectors is represented by this new vector.

For illustration, let's look at two vectors:

u = [3, 2, 1] and v = [1, 2, 3]

The vector represents the difference between u and v:

u - v = [3-1, 2-2, 1-3] = [2, 0, -2]

The following characteristics apply to vector subtraction:

• u - v = u + (-v)
• In general, vector subtraction is not commutative. In other words, u - v v - u

• There is a vector 0 such that for all vectors, u - 0 = u. u

Vector addition and subtraction are crucial operations in linear algebra and are frequently utilized in physics, engineering, and computer graphics, among other fields.

### Scalar Multiplication:

The following rule can be used to scale vectors by a scalar:

1. Divide the scalar by each element of the vector. As an illustration, 2[1, 2, 3] = [2, 4, 6].
2. The new vector has a different magnitude but the same direction as the initial vector.

Dot Product: The respective components of two vectors are multiplied, and the results are added, to determine the dot product, a scalar quantity. A dot () is placed between the vectors to represent the dot product. For illustration, [1, 2, 3] · [4, 5, 6] = 1×4 + 2×5 + 3×6 = 32.

### Dot Product:

1. Because A + B = B A, the dot product is commutative.
2. The distributive nature of the dot product means that A (B + C) = A B + A C.
3. The dot product and scalar multiplication are associated, therefore (aA) B = a(A B) = A (aB).
4. A vector's dot product with itself is equal to the square of its magnitude, therefore A A = ||A||2.

### Orthogonality:

Two vectors are referred to as being orthogonal in linear algebra if they are perpendicular to one another. This indicates geometrically that there is a 90-degree angle between the two vectors. Orthogonality is a key idea in linear algebra and is essential for many applications, including computer graphics, machine learning, and signal processing.

Formally, two vectors u and v are said to be orthogonal if their dot product is zero, which is represented by the formula: u v = 0. The sum of the products of the respective components of two vectors is known as the dot product. In other words, the vectors u and v have the following components: u1, u2,..., un, and v1, v2,..., vn.

Geometrically, the magnitude of two vectors u and v, and the cosine of the angle between them are combined to form the dot product. The formula is as follows: u v = ||u|| ||v|| cos, where ||u|| and ||v|| are the magnitudes of the vectors u and v, respectively, and is the angle between them.

Orthogonal vectors have many crucial characteristics.

In the event that u and v are orthogonal, then ||u + v||2 = ||u||2 + ||v||2. This characteristic, which is comparable to the Pythagorean theorem for right triangles, is known as the Pythagorean theorem for vectors.

If a set of n vectors is pairwise orthogonal, then they are linearly independent, i.e., none of them can be expressed as a linear combination of the others; if u and v are orthogonal and neither of them is the zero vector, then they form a basis for a two-dimensional subspace of the vector space.

Orthogonality is a key idea in linear algebra and has numerous uses in areas including computer graphics, machine learning, and signal processing. For instance, orthogonal basis functions are employed in signal processing to represent signals as frequency components. Orthogonal matrices are used in machine learning to decorrelate features and decrease the dimensionality of data. Orthogonal projections are used in computer graphics to display 3D objects on a 2D screen.

## What Are Matrices ?

A rectangular array of numbers is called a matrix. Systems of linear equations and linear transformations can be represented using matrices. Matrices can be multiplied, scaled, added to, subtracted from, and transposed.

Notation:

Matrices are typically written in capital letters in linear algebra. The matrix A, for instance, can be expressed as A = [a11 a12 a13; a21 a22 a23; a31 a32 a33], where aij denotes the element that is located in the matrix's ith row and jth column. The matrix's rows are separated by a semicolon.

Addition and subtraction: The following rules can be used to add and subtract matrices:

1. Add or remove the corresponding matrices' entries. For instance, A + B = [a11+b11 a12+b12 a13+b13] and A - B = [a11-b11 a12-b12 a13-b13] and [a21+b21 a22+b22 a23+b23] and [a31+b31 a32+b32 a33+b33].
2. Like the original matrices, the outcome matrix has the same dimensions.

### Scalar Multiplication:

The following rule can be used to scale matrices by a scalar:

1.  Multiply each matrix element by the scalar. Consider the following formula: 2A = [2a11 2a12 2a13; 2a21 2a22 2a23; and 2a31 2a32 2a33].
2. The size of the generated matrix matches that of the original matrix.

### Multiplication of matrices:

Multiplication of matrices is the process of joining two matrices to create a third matrix. A dot (.) or the absence of any symbol is used to indicate matrix multiplication between the matrices. If A is [a11 a12; a21 a22] and B is [b11 b12; b21 b22], for instance, AB is [a11b11+a12b21; a11b12+a12b22; a21b11+a22b21; a21b12+a22b22].

Matrix multiplication's characteristics include:

1. Multiplication of matrices is associative; in other words, (AB)C = A(BC).
2. Multiplication of matrices is distributive over the addition of matrices, i.e., A(B + C) = AB + AC.

3. The distribution of matrix multiplication over scalar multiplication is a(AB) = (aA)B = A(aB).

### Transposition:

A matrix's transposition is created by flipping its rows and columns. AT stands for a matrix A's transposition. For instance, AT = [a11 a21; a12 a22] if A = [a11 a12; a21 a22].

The identity matrix is produced when a matrix's inverse is multiplied by the original matrix. A-1 stands for a matrix A's inverse. A square matrix with a non-zero determinant is required for a matrix to have an inverse.

Linear algebra has a wide range of applications, including those in physics, engineering, computer science, and economics.

The following are some uses for linear algebra:

1. Resolving systems of linear equations: Many real-world situations involve systems of linear equations, which can be resolved using linear algebra.
2. Computer graphics: To manipulate and change images and objects, linear algebra is employed in computer graphics.
3. Machine learning: To carry out tasks like data preprocessing, feature extraction, and dimensionality reduction, machine learning algorithms require linear algebra.
4. Quantum mechanics: Quantum states and operators are represented in quantum mechanics using linear algebra.

## Conclusion:

The study of vectors, matrices, and linear transformations is the focus of the foundational mathematical field known as linear algebra. The use of matrices and vectors is widespread and has applications in many disciplines, including physics, engineering, computer science, and economics. To build a solid foundation in the subject, it is essential to comprehend the fundamental concepts of linear algebra, including vector addition, scalar multiplication, matrix multiplication, and matrix inversion. Linear algebra is now a crucial component of several industries, including data science, machine learning, and artificial intelligence, thanks to technological breakthroughs. Learning linear algebra is so crucial for both academic as well as real-world applications in a variety of fields.