Linear Algebra 18.06 Unit 1 Flashcards
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Questions and Answers

What does the Row Picture represent?

  • Solutions of linear combinations
  • Vectors of the system of equations
  • Determinants of matrices
  • Plot points for each equation (correct)

    • The Column Picture involves turning each equation into what?

  • Matrices
  • Vectors (correct)
  • Rows
  • Solutions

    • What is the result of multiplying matrix A by vector x?

    The resulting vector.

    What signifies linear independence for matrix A?

    <p>Can we solve Ax = b for every vector b?</p> Signup and view all the answers

    The product of pivots equals what?

    <p>The determinant.</p> Signup and view all the answers

    What does elimination involve?

    <p>Multiplying A with elimination matrices E.</p> Signup and view all the answers

    What must the inverse of elimination matrices do?

    <p>Undo the operations performed by the original matrix.</p> Signup and view all the answers

    What is the standard method of matrix multiplication?

    <p>c(i,j) = Sum of (a(i,k)*b(k,j)) from k=0 to n</p> Signup and view all the answers

    What is the Inverse Matrix?

    <p>A^-1 * A = I</p> Signup and view all the answers

    What is the result of the product of two matrices AB's transpose?

    <p>B.T * A.T</p> Signup and view all the answers

    Is R.T * R symmetric?

    <p>True</p> Signup and view all the answers

    Is (A+B).T = A.T + B.T true?

    <p>True</p> Signup and view all the answers

    Is AB = BA always true?

    <p>False</p> Signup and view all the answers

    What is a vector space?

    <p>A collection of elements formed by adding or multiplying vectors.</p> Signup and view all the answers

    What defines a subspace?

    <p>A vector space contained within another vector space.</p> Signup and view all the answers

    Is the intersection of two subspaces also a subspace?

    <p>True</p> Signup and view all the answers

    What must all subspaces contain?

    <p>The zero vector.</p> Signup and view all the answers

    How do you find the null space of a matrix?

    <p>Perform elimination to get to echelon form and identify free columns.</p> Signup and view all the answers

    Study Notes

    Row Picture

    • Represents plot points for each equation in a system.
    • The solution to the system is the intersection of the plotted lines.

    Column Picture

    • Converts each equation into vectors, showing them as columns.
    • Solutions arise from the linear combination of these vectors.

    Matrix Picture

    • Involves multiplying matrix A with vector x to produce a resulting vector.

    Linear Independence

    • Determines if the vector equation Ax = b can be solved for every vector b.
    • If not solvable, the vectors are linearly dependent and the matrix is singular.

    Product of Pivots

    • The product of pivots in a matrix equals its determinant.

    Elimination

    • Applies elimination matrices E to matrix A to convert it into an upper triangular form U.
    • Back substitution is used to find solutions for vector x.

    Inverse of Elimination Matrices

    • The inverse operation of an elimination matrix must undo the elimination performed.

    Matrix Multiplication Methods

    • Standard method: c(i,j) = Sum of (a(i,k) * b(k,j)).
    • Column method: Resulting column J of C comes from multiplying matrix A with column J of B.
    • Row method: Resulting column I of C comes from multiplying row I of A with matrix B.
    • Column*Row method: Sum from row k of A and column k of B.
    • Block method: Involves dividing matrices into blocks for dot product operations.

    Inverse Matrix

    • Defined by the property A^-1 * A = I.
    • Matrices with determinant 0 do not have an inverse.

    Gauss-Jordan Elimination

    • Augments matrices A and I, using elimination to transform A into I, while simultaneously converting I to A^-1.

    Inverse of Matrix Product

    • The inverse of a product of matrices is (B^-1) * (A^-1).

    Transpose of Matrix Product

    • The transpose of a product is given by B^T * A^T.

    Inverse of Transpose

    • The inverse of the transpose of a matrix is equal to the transpose of the inverse, (A^-1)^T.

    LU Decomposition vs. EA = U

    • LU decomposition emphasizes the effects of linear operations with L, while EA = U reflects multiple operations from E.

    Complexity of Eliminations

    • For an n*n matrix, the complexity of the elimination process is (1/3)n^3.

    Permutation Matrix

    • An identity matrix with rows swapped, with n! different permutations for an n*n identity matrix.
    • The inverse of a permutation matrix is its transpose, P^-1 = P^T, primarily used for row swapping.

    Symmetric Matrix

    • A matrix is symmetric if its transpose equals itself, A^T = A.

    Transpose of Product of Matrices

    • R^T * R is symmetric due to the nature of transposition.

    Properties of Transposition

    • (A + B)^T = A^T + B^T is true.
    • (cA)^T = c(A^T) is also true.

    Commutativity of Matrix Multiplication

    • AB = BA is false; matrix multiplication is not commutative.

    Vector Space

    • A vector space is formed by vectors that can be added together or multiplied, closed under these operations.

    Subspace

    • A subset of a vector space that is also closed under addition and multiplication.

    Union of Subspaces

    • The union of two subspaces is generally not a subspace due to sum vectors potentially falling outside the union.

    Intersection of Subspaces

    • The intersection of two subspaces is always a subspace since it is closed under linear combinations.

    Column Space

    • Comprises all vectors b for which the equation Ax = b has a valid solution.
    • All b vectors can be expressed as linear combinations of the columns of A.

    Null Space

    • Consists of all vectors x satisfying the equation Ax = 0.

    Zero Vector in Subspaces

    • All subspaces must include the zero vector.

    Finding Null Space

    • Achieve echelon form by elimination; identify pivot and free columns, substituting free columns with 1 and 0s to find vectors in the null space.

    Reduced Row Echelon Form

    • First transform to echelon form, then back-substitute to obtain a structure of [[I, F], [0, 0]].
    • The null space can be expressed as [[-F], [I]], indicating solutions in relation to leading variables.

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    Test your understanding of key concepts in linear algebra with these flashcards. Cover fundamentals such as row, column, and matrix representations of equations. Perfect for reinforcing your knowledge of linear systems and vector spaces.

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