Podcast
Questions and Answers
Which of the following operations is NOT considered an elementary row operation?
Which of the following operations is NOT considered an elementary row operation?
- Swapping two rows.
- Multiplying a row by a constant.
- Squaring all elements in a row. (correct)
- Adding a multiple of one row to another.
What is a key property of all elementary matrices?
What is a key property of all elementary matrices?
- They are symmetric.
- They are diagonal.
- They are invertible. (correct)
- They are not invertible.
According to the Invertible Matrix Theorem, if a square matrix A is invertible, what must be true about the equation $Ax = b$?
According to the Invertible Matrix Theorem, if a square matrix A is invertible, what must be true about the equation $Ax = b$?
- It has either no solution or infinitely many solutions.
- It has a unique solution for every b. (correct)
- It has no solution for some b.
- It has infinitely many solutions for every b.
If a matrix can be expressed as the product of elementary matrices, what can be concluded about the matrix?
If a matrix can be expressed as the product of elementary matrices, what can be concluded about the matrix?
Why is finding the determinant of a matrix useful?
Why is finding the determinant of a matrix useful?
What is the determinant of a 1x1 matrix equal to?
What is the determinant of a 1x1 matrix equal to?
What geometric quantity does the absolute value of the determinant of a 2x2 matrix represent, when the columns of the matrix are considered as vectors?
What geometric quantity does the absolute value of the determinant of a 2x2 matrix represent, when the columns of the matrix are considered as vectors?
What are the smaller sub-matrices called when computing determinants by expanding along rows or columns?
What are the smaller sub-matrices called when computing determinants by expanding along rows or columns?
In the context of determinants, what is a 'minor'?
In the context of determinants, what is a 'minor'?
What is the relationship between minors and cofactors in determinant calculation?
What is the relationship between minors and cofactors in determinant calculation?
If you swap two rows of a matrix, how does it affect the determinant?
If you swap two rows of a matrix, how does it affect the determinant?
What does multiplying a row of a matrix by a scalar multiple do to the determinant?
What does multiplying a row of a matrix by a scalar multiple do to the determinant?
What happens to the determinant if you add a multiple of one row to another row in a matrix?
What happens to the determinant if you add a multiple of one row to another row in a matrix?
How is the adjoint of a matrix related to its cofactors?
How is the adjoint of a matrix related to its cofactors?
Which of the following is a condition for a matrix to be invertible, according to the Invertible Matrix Theorem?
Which of the following is a condition for a matrix to be invertible, according to the Invertible Matrix Theorem?
What does Cramer's Rule provide?
What does Cramer's Rule provide?
In Cramer's Rule, if you are solving for $x_i$ in the system $Ax = b$, what do you do to the matrix A?
In Cramer's Rule, if you are solving for $x_i$ in the system $Ax = b$, what do you do to the matrix A?
What characterizes a 'sparse matrix'?
What characterizes a 'sparse matrix'?
Why might Cramer's Rule be particularly useful, despite potentially high computational cost?
Why might Cramer's Rule be particularly useful, despite potentially high computational cost?
What two operations must be defined for a set of objects to be considered a vector space?
What two operations must be defined for a set of objects to be considered a vector space?
What does it mean for a set to be 'closed' under an operation in the context of vector spaces?
What does it mean for a set to be 'closed' under an operation in the context of vector spaces?
In the vector space $R^3$, what is a general vector written as a linear combination of?
In the vector space $R^3$, what is a general vector written as a linear combination of?
Which of the following is NOT a condition that must be satisfied for a set to be considered a vector space?
Which of the following is NOT a condition that must be satisfied for a set to be considered a vector space?
Which set can be classified to follow the basic conditions for a Vector Space?
Which set can be classified to follow the basic conditions for a Vector Space?
Which of the following sets, with the usual operations of addition and scalar multiplication, forms a vector space?
Which of the following sets, with the usual operations of addition and scalar multiplication, forms a vector space?
Given that polynomials with real coefficients follow Vector Space rules, which additional piece of information is needed to prove this?
Given that polynomials with real coefficients follow Vector Space rules, which additional piece of information is needed to prove this?
For any vector space V over a field F, and for any vector v in V, what must be true about the zero vector?
For any vector space V over a field F, and for any vector v in V, what must be true about the zero vector?
If $c$ is a scalar from the field F and $0$ is the zero vector in vector space V, then what is the result of $c * 0$?
If $c$ is a scalar from the field F and $0$ is the zero vector in vector space V, then what is the result of $c * 0$?
Under what condition, for scalar $c$ in field $F$, and vector $v$ in vector space $V$ can $cv = 0$?
Under what condition, for scalar $c$ in field $F$, and vector $v$ in vector space $V$ can $cv = 0$?
What is a subspace?
What is a subspace?
Which condition must be met for a subset W of a vector space V to be considered a subspace of V?
Which condition must be met for a subset W of a vector space V to be considered a subspace of V?
What is a key difference between any subset of a vector space and being closed under two separate operations?
What is a key difference between any subset of a vector space and being closed under two separate operations?
What is one of the first things you can check to see if a subset is actually a subspace of another?
What is one of the first things you can check to see if a subset is actually a subspace of another?
What is the null space of a matrix A?
What is the null space of a matrix A?
According to Theorem 4.3.12, what statement is correct about the null space?
According to Theorem 4.3.12, what statement is correct about the null space?
If a subset $S$ of a vector space $V$ does not contain the zero vector, what can be concluded?
If a subset $S$ of a vector space $V$ does not contain the zero vector, what can be concluded?
What is a sufficient check to determine if a solution to an equation is a subspace for (or)?
What is a sufficient check to determine if a solution to an equation is a subspace for (or)?
If a matrix A has an inverse, and that inverse is matrix B, what is the result of multiplying matrix A by matrix B?
If a matrix A has an inverse, and that inverse is matrix B, what is the result of multiplying matrix A by matrix B?
How does the invertibility of an elementary matrix relate to its row operations?
How does the invertibility of an elementary matrix relate to its row operations?
According to the Invertible Matrix Theorem, which of the following conditions ensures that a square matrix A is invertible?
According to the Invertible Matrix Theorem, which of the following conditions ensures that a square matrix A is invertible?
Why is it useful to know if a matrix can be expressed as the product of elementary matrices?
Why is it useful to know if a matrix can be expressed as the product of elementary matrices?
If the columns of a 2x2 matrix are viewed as vectors forming a parallelogram, and the determinant of this matrix is zero, what can be said about the area of the parallelogram?
If the columns of a 2x2 matrix are viewed as vectors forming a parallelogram, and the determinant of this matrix is zero, what can be said about the area of the parallelogram?
In calculating the determinant using cofactor expansion, how do you determine the sign (positive or negative) associated with each cofactor?
In calculating the determinant using cofactor expansion, how do you determine the sign (positive or negative) associated with each cofactor?
How does the determinant of a matrix $A$ relate to the determinant of its adjoint, adj$(A)$, when $A$ is a $n \times n$ matrix?
How does the determinant of a matrix $A$ relate to the determinant of its adjoint, adj$(A)$, when $A$ is a $n \times n$ matrix?
According to the Invertible Matrix Theorem, which of the following statements is true about the determinant of an invertible matrix A?
According to the Invertible Matrix Theorem, which of the following statements is true about the determinant of an invertible matrix A?
In using Cramer's Rule to solve a system of linear equations, what happens if the determinant of the coefficient matrix A is zero?
In using Cramer's Rule to solve a system of linear equations, what happens if the determinant of the coefficient matrix A is zero?
What is the primary advantage of using cofactor expansion to find the determinant of a sparse matrix?
What is the primary advantage of using cofactor expansion to find the determinant of a sparse matrix?
If a set of vectors in $R^n$ fails to meet the condition of closure under scalar multiplication, what can be concluded about the set?
If a set of vectors in $R^n$ fails to meet the condition of closure under scalar multiplication, what can be concluded about the set?
In the context of vector spaces, what does it mean for a vector space to be 'closed' under vector addition?
In the context of vector spaces, what does it mean for a vector space to be 'closed' under vector addition?
Consider a set $S$ of all 2x2 matrices with real entries where the determinant of each matrix is equal to 1. With standard matrix addition, and scalar multiplication, is this set closed under addition?
Consider a set $S$ of all 2x2 matrices with real entries where the determinant of each matrix is equal to 1. With standard matrix addition, and scalar multiplication, is this set closed under addition?
What distinguishes a subspace from any arbitrary subset of a vector space?
What distinguishes a subspace from any arbitrary subset of a vector space?
If W is a subspace of V, and V is a vector space, which of the following operations when applied to elements of W is guaranteed to result in an element that is also in W?
If W is a subspace of V, and V is a vector space, which of the following operations when applied to elements of W is guaranteed to result in an element that is also in W?
What condition regarding the zero vector is necessary for a subset $W$ of a vector space $V$ to potentially be a subspace of $V$?
What condition regarding the zero vector is necessary for a subset $W$ of a vector space $V$ to potentially be a subspace of $V$?
If $W$ is the null space of matrix $A$, then for any vector $x$ in $W$, what is the result of $Ax$?
If $W$ is the null space of matrix $A$, then for any vector $x$ in $W$, what is the result of $Ax$?
Theorems regarding the Null Space detail that the set of solutions to $Ax = 0$ form a...
Theorems regarding the Null Space detail that the set of solutions to $Ax = 0$ form a...
If a non-empty subset $S$ of a vector space $V$ does NOT satisfy the condition that for all vectors $u$ and $v$ in $S$, the sum $u + v$ is also in $S$, what can be definitively concluded?
If a non-empty subset $S$ of a vector space $V$ does NOT satisfy the condition that for all vectors $u$ and $v$ in $S$, the sum $u + v$ is also in $S$, what can be definitively concluded?
To determine if the solution set of a nonhomogeneous linear system $Ax = b$ (where $b \neq 0$) is a subspace, what is the most efficient first step?
To determine if the solution set of a nonhomogeneous linear system $Ax = b$ (where $b \neq 0$) is a subspace, what is the most efficient first step?
Flashcards
Elementary Row Operations
Elementary Row Operations
Elementary row operations include swapping rows, multiplying a row by a constant, and adding a multiple of one row to another.
Invertibility of Elementary Matrices
Invertibility of Elementary Matrices
All elementary matrices are invertible, and the inverse of an elementary matrix is another elementary matrix.
Invertible Matrix Theorem
Invertible Matrix Theorem
If A is invertible, then Ax = b has a unique solution for every b.
Rank and Row Reduction
Rank and Row Reduction
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Determinant and Invertibility
Determinant and Invertibility
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What is a Determinant?
What is a Determinant?
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Determinant as Area
Determinant as Area
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Minors
Minors
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Method of Minors
Method of Minors
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Determinants and Row Operations
Determinants and Row Operations
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Cofactor Definition
Cofactor Definition
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Cramer's Rule
Cramer's Rule
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Vector Space
Vector Space
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Closure Property
Closure Property
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Vector Space Properties
Vector Space Properties
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3D Vector Representation
3D Vector Representation
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Subspace
Subspace
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Zero Vector Check
Zero Vector Check
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Study Notes
- Day 13 discusses finding inverse matrices
Announcements
- Today involves groups
- Invertible Matrix Theorem is in Section 2.8
- Determinants can be found in Section 3.1
- Grading is in progress
- In-class exams grading is back
- Old discussion board posts are not graded
Elementary Matrices
- Section 2.7 covers elementary matrices
- Elementary row operations include swapping, multiplying by a constant, and adding a multiple of one row to another
Elementary Matrices (cont.)
- All elementary matrices are invertible and their inverses are also elementary matrices
- Row reduction can be expressed by pre-multiplying elementary matrices by the matrix
The Invertible Matrix Theorem
- If a matrix is invertible, the equation has a unique solution
- If an equation has a unique solution then it only has a trivial solution
- If a matrix has a rank, row reduction can be done using elementary row operations
Determinants
- Chapter 3 briefly mentions determinants
- Determinants are a way to determine if a matrix is invertible
- Determinants are a single number calculated from entries in a matrix
- A square matrix is invertible if and only if its determinant meets a certain condition, to be proved later
Determinants by Cases
- Case 1: a 1 x 1 matrix
- Case 2: a 2x2 matrix with row reduction
Geometry of Determinants
- Area of a parallelogram is equal to base x perpendicular height
- The definition of cross product is mentioned
Determinants by Cases (cont.)
- Case 1: a 1 x 1 matrix
- Case 2: a 2x2 matrix
- Case 3 is labeled "oh no"
Determinants: 3 x 3: Sarrus' Rule
- Sarrus' Rule covers finding determinants for 3x3 matrices
Determinants: 3 x 3 (cont.)
- The determinant calculation becomes complicated
- Smaller sub-matrices are called minors
Groups
- Groups and spring break plans are related to finding determinants and invertibility
Method of Minors (Groups)
- What did you do over spring break?
Determinants and Row Reduction
- Matrices with lots of zeros are considered "nice"
- Swapping two rows has an impact, think about the 2x2 case
- Multiplying a row by a scalar multiple has an impact
- Adding a multiple of one row to another has an impact
Minors vs. Cofactors
- The method of minors is the same as "cofactor expansion"
- The cofactor is the determinant of the minor times a sign (-1)^(i+j)
- The adjoint is the transpose of the matrix, but each element has been replaced by its cofactor
Cramer's Rule
- If a system has a unique solution
- Then is the matrix with a column replaced
Cramer's Rule Example
- Solve a system using the usual way as well as Cramer's Rule
Why Use Cramer's Rule and Cofactor Expansion?
- Cramer’s Rule is useful for proving further theorems
- Cofactor expansion is useful when there are a lot of zeros
- Sparse Matrix: 50% or more zero entries
- People developed some of these methods for numerical stability
Real Vector Space
- A vector space is defined by a set of objects and two operations
- Objects in this case are vectors
- Operations are addition and scalar multiplication by a real number
- The set is closed under the operations; the result is another vector
Real Vector Space (cont)
- Scalar multiplication of vectors has certain properties
- Discusses vector multiplication, cross products or dot products
Familiar Special Case in 3D space
- Focuses on "unit vectors" and a "standard basis"
- A general vector can be written as a linear combination of three unit vectors
Vector Spaces: Properties
- A non-empty set must have closure under addition and closure under scalar multiplication
- It must follow commutativity and associativity of addition
- It must have a zero vector (additive identity) and existence of additive inverses
- Includes a unit property or multiplicative identity
- Associativity of scalar multiplication over vector addition is necessary
- Distributive property of scalar multiplication over vector addition
- Distributive property of scalar multiplication over scalar addition is required
Vector Spaces: Examples
- Consider the set of 2 x 2 matrices
- Or consider the set of complex numbers
Differential Equations Context
- Discusses the most basic spring-mass system
- Vector Spaces - Not Just for Vectors Anymore
More examples of vector spaces
- Real or complex vectors
- Matrices with real or complex entries
- The set of all polynomials of degree with real coefficients
- Set of all real-valued functions continuous on the interval
- Have at least derivatives all continuous on the interval
Vector Space of Polynomials
- Let be a non-empty set ,the set of all polynomials of degree with real coefficients
- Define 2 operations: addition and scalar multiplication
- Scalar in or
- Ten conditions must be satisfied
Nice Properties of Vector Spaces
- Theorem 4.2.7: Let be a vector space. Then ( is either or )
- The zero vector is unique
- and If is a scalar and such that then either or.
Polynomial Vector Space Example
- Closure under addition and closure under scalar multiplication
Subspaces of a Vector Space
- A nonempty subset of a vector space is a subspace if itself is a vector space under the operations
- This is closed under the operations of addition and scalar multiplication in
Theorem 4.3.2: "Thank Goodness"
- Let be a nonempty subset of a vector space. Then a closed subspace meets this theorem
Solutions of a Linear System
- Solving a linear system
- Zero Vector Check
The Null Space Theorem 4.3.12
- The solution set of the homogenous linear system is a subspace of (or) called the null space
- If there are two vectors that are solutions, and, so +, and so it’s closed under +, the null space criteria has been met
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