IEEE 754 Single Precision Quiz

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Questions and Answers

In the context of floating-point numbers, what does the mantissa represent?

  • The exponent of the number
  • The base of the number
  • The sign of the number
  • The significant digits of the number (correct)

In the IEEE standard for single precision floating-point numbers, the mantissa's first digit is explicitly stored.

False (B)

What is the bias (K) used in the IEEE single precision floating-point representation?

127

In the IEEE single precision format, an exponent of 255 with a non-zero mantissa represents ______.

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

What does S represent in the IEEE single precision floating-point format?

<p>Sign (D)</p> Signup and view all the answers

Subnormal numbers have an exponent e = 255 in the IEEE single precision format.

<p>False (B)</p> Signup and view all the answers

What base (B) is assumed in the IEEE standard as described?

<p>2</p> Signup and view all the answers

Match the following floating-point representations with their meanings in the IEEE 754 single precision standard:

<p>e = 0, m = 0 = Represents zero e = 255, m != 0 = Represents NaN (Not a Number) e = 255, m = 0 = Represents Infinity 0 &lt; e &lt; 255 = Represents a normal number</p> Signup and view all the answers

Which of the following stopping criteria uses the absolute difference of successive approximations?

<p>$|x_{k+1} - x_k| &lt; tol$ (A)</p> Signup and view all the answers

A small residual $r_k = b - Ax_k$ guarantees a small error $x_k - x$ in solving a linear system $Ax = b$.

<p>False (B)</p> Signup and view all the answers

What type of matrix results from Gaussian elimination?

<p>Upper triangular matrix</p> Signup and view all the answers

Gaussian elimination can be written in compact from as PA = ______ where P denotes a permutation matrix

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

Match the matrix factorization with its corresponding matrix type:

<p>LU factorization = General square matrices Cholesky factorization = Symmetric positive definite matrices Givens rotations = Sparse matrices</p> Signup and view all the answers

What does 'tol' represent in the stopping criteria formulas?

<p>A specified tolerance (A)</p> Signup and view all the answers

Gaussian elimination is applicable only to singular matrices.

<p>False (B)</p> Signup and view all the answers

In the context of solving $f(x) = 0$, what is the residual $r_k$?

<p>$f(x_k)$</p> Signup and view all the answers

Which of the following is a necessary condition for a matrix $A ∈ R^{n×n}$ to be symmetric positive definite?

<p>$A^T = A$ and $x^T Ax &gt; 0$ for all $x ≠ 0$ (C)</p> Signup and view all the answers

If a matrix $A$ is symmetric positive definite, all its diagonal entries must be positive.

<p>True (A)</p> Signup and view all the answers

What is the result of Gaussian elimination on a symmetric positive definite matrix A without pivoting?

<p>A = LU with U = DLT</p> Signup and view all the answers

The Cholesky factorization of a symmetric positive definite matrix A is given by $A = ______ · R$.

<p>R^T</p> Signup and view all the answers

Match the following matrix properties with their implications:

<p>Symmetric Positive Definite = All eigenvalues are positive Principal Submatrix = Symmetric positive definite Largest Entry in Absolute Value = Located on the diagonal and positive L has rank m, then $LAL^T$ = Symmetric positive definite.</p> Signup and view all the answers

Given the Cholesky factorization $A = R^T R$, what type of matrix is R?

<p>Upper triangular (D)</p> Signup and view all the answers

Cholesky factorization requires pivoting for symmetric positive definite matrices in exact arithmetic.

<p>False (B)</p> Signup and view all the answers

How many operations are required to perform Cholesky factorization directly?

<p>1/3 n^3 + O(n^2)</p> Signup and view all the answers

What are the values of 'c' and 's' in the rotation matrix given that $Q = \begin{bmatrix} c & -s \ s & c \end{bmatrix}$?

<p>$c = \frac{a_{11}}{\sqrt{a_{11}^2 + a_{21}^2}}$, $s = \frac{-a_{21}}{\sqrt{a_{11}^2 + a_{21}^2}}$ (A)</p> Signup and view all the answers

The matrix $Q$ defined as $Q = \begin{bmatrix} c & -s \ s & c \end{bmatrix}$, where $s = \sin(\alpha)$ and $c = \cos(\alpha)$ for some angle $\alpha$, is an orthogonal matrix if and only if $c^2 + s^2 = 1$.

<p>True (A)</p> Signup and view all the answers

What condition must be satisfied for the product of a matrix $Q$ and its transpose $Q^T$ to equal the identity matrix $I$?

<p>$Q^T Q = I$</p> Signup and view all the answers

A matrix Q is considered __________ if its transpose multiplied by itself equals the identity matrix.

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

Match the following matrix properties with their descriptions:

<p>Orthogonal Matrix = Its transpose multiplied by itself equals the identity matrix. Rotation Matrix = A matrix that represents a rotation in space. Identity Matrix = A square matrix with ones on the main diagonal and zeros elsewhere. Transpose of a Matrix = A matrix formed by interchanging the rows and columns of a given matrix.</p> Signup and view all the answers

In the context of rotation matrices, what does the condition $(QA)_{21} = 0$ imply?

<p>It implies that the dot product of the second row of Q and the first column of A is zero. (B)</p> Signup and view all the answers

The $Q_{ij,k}$ matrix is always a $2 \times 2$ matrix.

<p>False (B)</p> Signup and view all the answers

In the $n \times n$ matrix $Q_{ij,k}$, what are the diagonal elements other than $c$ and $s$?

<p>1</p> Signup and view all the answers

What is the condition number of matrix A, denoted as κ∞(A)?

<p>4000 (A)</p> Signup and view all the answers

The actual relative error is larger than the upper bound provided by Theorem 3.7.

<p>False (B)</p> Signup and view all the answers

What is the numerical solution vector obtained by using MATLAB's backslash on the matrix A?

<p>[0.999999999974, 1.999999999951, 3.000000000039, 4.000000000032]</p> Signup and view all the answers

The relative error from the numerical solution amounts to approximately ___ x 10^{-11}.

<p>1.369</p> Signup and view all the answers

Which of the following statements is true regarding the matrix A?

<p>It has an upper bound error of 1.3 x 10^{-10}. (B)</p> Signup and view all the answers

Match the following values with their descriptions:

<p>κ∞(A) = 4000 Actual relative error = 4.002 Upper bound error = 4.004 Condition number context = Stable computation by MATLAB</p> Signup and view all the answers

The solution vector x is defined as [___].

<p>[1, 2, 3, 4]</p> Signup and view all the answers

What is the value of K(A) described in the document?

<p>6.01 x 10^5 (A)</p> Signup and view all the answers

According to Theorem 3.7, what condition must be met to ensure a certain bound when comparing the solutions of two linear systems $Ax = b$ and $A'x = b'$?

<p>$\epsilon_A \cdot K(A) &lt; 1$ (A)</p> Signup and view all the answers

For all induced norms, the values $\epsilon_A$ and $\epsilon_b$ are equal to $\bar{
ewline \\epsilon}_A$ and $\bar{
ewline \\epsilon}_b$ respectively, as defined in Theorem 3.7.

<p>False (B)</p> Signup and view all the answers

In the special case where $A' = A$, according to Theorem 3.7, what is the upper bound for the relative error $\frac{||x' - x||}{||x||}$?

<p>$K(A) \cdot \epsilon_b$</p> Signup and view all the answers

According to Theorem 3.7, if $A$ is invertible and $\epsilon_A \cdot K(A) < 1$, then there exists a relation with the ______ number $K(A)$.

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

Match the terms from Theorem 3.7 with their descriptions:

<p>K(A) = Condition number of matrix A \epsilon_A = Bound on relative change in matrix elements \epsilon_b = Bound on relative change in vector b x = Solution vector to the original system</p> Signup and view all the answers

In the context of perturbed linear systems (Theorem 3.7), what do $\epsilon_A$ and $\epsilon_b$ represent?

<p>Relative errors in A and b, respectively (B)</p> Signup and view all the answers

Theorem 3.7 provides a way to quantify the sensitivity of the solution of a linear system to perturbations in the matrix A and the vector b.

<p>True (A)</p> Signup and view all the answers

According to Theorem 3.7, the condition number $K(A)$ relates to the [blank] of a matrix.

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

Flashcards

Floating Point Number

A representation of real numbers in a way that can support a wide range of values.

Mantissa

The part of a floating point number that contains its significant digits.

Exponent

The part of a floating point number that indicates the scale or magnitude of the number.

Bias

A constant used in floating point representation to allow for both positive and negative exponents.

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IEEE Standard

A widely adopted standard for floating point computation used by computers.

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Single Precision

A floating point representation that uses 32 bits, typically with 1 sign bit, 8 exponent bits, and 23 mantissa bits.

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Normal Numbers

Floating point numbers with a non-zero exponent, covering a significant range of values.

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Exceptions in Floating Point

Special cases like NaN (Not a Number) and Infinity that occur in floating point arithmetic.

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Stopping criteria

Rules to decide when to stop the iterations based on approximation accuracy.

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Successive approximations

A sequence of approximation values generated in iterative methods.

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Absolute difference

The calculation of the difference between two successive approximations.

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Relative difference

The difference between successive approximations relative to the size of the new approximation.

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Residual

The error measure defined as f(x) = b - Ax in the context of finding roots.

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Gaussian elimination

A method for solving linear systems by transforming to upper triangular form.

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LU factorization

Decomposing a matrix A into a product of a lower triangular matrix L and an upper triangular matrix U.

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Cholesky factorization

A special factorization technique for symmetric positive definite matrices.

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Symmetric Matrix

A matrix A is symmetric if AT = A.

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Positive Definite Matrix

A matrix A is positive definite if xT Ax > 0 for all x ≠ 0.

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Principal Submatrix

A principal submatrix is formed by deleting any number of rows and corresponding columns from a matrix.

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Diagonal Entries

The diagonal entries of a matrix are the elements Aii where i = j.

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Cholesky Decomposition

A Cholesky decomposition factors a symmetric positive definite matrix A into A = RT R, where R is upper triangular.

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Eigenvalues

Eigenvalues of a matrix are scalars related to linear transformations, often determining stability in systems.

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Orthogonal Matrix

A square matrix Q where QT Q = I, meaning it's orthogonal if its transpose is its inverse.

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Rotation Matrix

A matrix used to rotate points in the Euclidean space, defined by angle α with components involving sin and cos.

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Variables s and c

s := sin α and c := cos α, representing sine and cosine of angle α in the rotation matrix.

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Setting QA21 = 0

Condition to zero out a specific entry in a matrix product using rotation parameters.

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a11 and a21

Elements of a 2x2 matrix involved in the transformation using the rotation matrix.

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Generalization to n × n Matrix

Expanding the concept of 2x2 rotation matrices to larger matrices with defined rotational components.

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Qij,k

A general rotation matrix representing a plane rotation in an n-dimensional space.

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Trigonometric Relationships in Matrices

Using sine and cosine functions in matrix transformations to establish orthogonality.

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Condition Number κ∞

A measure of the sensitivity of a matrix A's solution to changes in b, calculated as κ∞(A) = ||A||∞ ||A⁻¹||∞.

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Theorem 3.7

It provides an upper bound on the relative error in numerical solutions based on conditioning of matrix A.

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Relative Error

The measure of the difference between the estimated and actual values relative to the actual value, expressed as ||x - x||b / ||x||.

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Matrix A

A specific 4x4 matrix used in solutions, indicating the transitions of outputs based on the input vector x.

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Numerical Solution x

The vector result of solving an equation Ax = b using numerical methods, showing slight variations due to computational approximation.

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MATLAB Backslash

A MATLAB operator used to solve linear equations of the form Ax = b efficiently, utilizing numerical stability.

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Upper Bound for Error

The maximum allowable relative error determined by the condition number and machine precision in numerical solutions.

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Machine Precision (eps)

The smallest difference recognizable by a computer, affecting numerical calculations and errors.

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Condition of the solution

Describes how solutions to linear systems behave under perturbations of coefficients.

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Perturbation of coefficients

Adjustments in matrix A and vector b by factors eij and ei.

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Condition number K(A)

Measures sensitivity of a matrix's solution to changes in inputs.

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Induced norms

Function to measure sizes of matrices and vectors, used here for errors.

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Invertible matrix A

A matrix is invertible if there exists another matrix that multiplies it to yield the identity matrix.

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Error bounds

Limits on the errors in computed solutions derived from theorem 3.7.

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1-norm and infinity norm

Specific ways to compute the size of a vector or matrix, affecting error measurement.

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Study Notes

Numerical Mathematics 1 Course Outline

  • Prof. Dr. Sabine Le Borne
  • Hamburg University of Technology
  • October 11, 2024

Contents

  • Chapter 1: Introduction

    • Numerical Mathematics (Scientific Computing) deals with techniques for solving technical and scientific problems using computers.
  • Chapter 2: Finite Precision Arithmetic

    • 2.1 Machine Numbers:
      • Computers use finite approximations of real numbers.
      • IEEE standard for floating-point representation (single and double precision).
      • Normal numbers, subnormal numbers, NaN (Not a Number), and inf (infinity).
    • 2.1.2 Rounding to Machine Numbers:
      • Rounding errors are inherent in computer arithmetic.
      • Upper bounds for absolute and relative rounding errors.
      • Significant figures and machine precision.
    • 2.1.3 Computer Arithmetic:
      • Error analysis for basic arithmetic operations (+, -, *, /).
      • Rounding errors in arithmetic operations, cancellation.
    • 2.1.4 Cancellation:
      • Loss of precision when subtracting similar numbers.
    • 2.2 Condition of a Problem and Stability of an Algorithm:
      • Condition number measures problem sensitivity to input variations.
      • Stability of an algorithm describes how rounding errors propagate.
      • Norms (vector and matrix) are used to measure quantities.
      • Landau symbols describe asymptotic behavior.
    • 2.2.1 Norms
      • Definitions and examples of vector norms (2-norm, infinity norm, 1-norm)
    • 2.2.2 Landau Symbols
      • Definitions for Big-O and little-o notations.
    • 2.2.3 Condition number of a problem: - Definition of the condition number of a problem in an appropriate norm.
      • 2.2.4 Stability of an algorithm:
        • Definition of stability of an algorithm and relationship to conditioning.
    • 2.2.5 Stopping Criteria: - Methods to determine when an approximation is good enough - Stopping criterion based on the relative difference of two successive approximations. - Criteria based on the residual of an iterative method
  • Chapter 3: Linear Systems of Equations

    • 3.1 Gaussian Elimination:
      • Algorithm for solving linear systems Ax = b.
      • LU factorization (row permutations, forward elimination, back substitution).
      • 3.2 and 3.3: Condition of linear systems of equations, Cholesky decomposition
    • 3.4 Elimination with Givens rotations:
      • Algorithm for solving linear systems using orthogonal/unitary transformations.
  • Chapter 4: Interpolation

    • 4.1 Polynomial Interpolation:
      • Finding a polynomial that passes through given points (xi, yi).
      • Vandermonde matrix approach (direct method); Lagrange polynomials; Barycentric formula and Newton's formula; other methods
      • Error analysis for interpolation.
      • Polynomial interpolation schemes differ in efficiency and numerical stability.
    • 4.2 Piecewise Interpolation with Polynomials:
      • Spline interpolation: piecewise polynomials that are differentiable (as many times as possible) at connecting points. Types of splines: classical cubic splines. Boundary conditions, natural boundary conditions, Not-a-knot conditions.
    • 4.3 and 4.4: trigonometric interpolation, connection between interpolation schemes
  • Chapter 5: Nonlinear Equations

    • 5.1 Scalar Nonlinear Equations: Solving f(x) = 0. Methods:
      • Bisection method; fixed point iteration (convergence analysis).
      • Secant method; Newton's method.
      • 5.2 Nonlinear Systems of Equations
        • Multivariate Taylor expansion, Jacobian matrix, Broyden methods.
  • Chapter 6: Least Squares Problems

    • 6.1 Linear Least Squares Problems: - Least squares problems; normal equations.
    • 6.2 Singular Value Decomposition:
      • SVD decomposition of matrices, pseudoinverse.
    • 6.3 Condition of linear least squares problems:
      • Sensitivity of solutions to errors in inputs, implications for solving linear least squares problems, regularization (e.g. Tikhonov regularization).
    • 6.4 Solving linear least squares using QR factorization: QR factorization of matrices; methods of Householder and Givens rotations; Gram Schmidt orthogonalization.
    • 6.5 Nonlinear Least Squares Problems:
      • Using Newton's method, Gauss-Newton method.
      • Levenberg-Marquardt algorithm.
  • Chapter 7: Eigenvalue Problems

    • Review of eigenvalue theory;
    • Power methods (convergence);
  • QR algorithm.

  • Chapter 8: Differentiation

    • Finite difference approximation.
  • Chapter 9: Quadrature

  • Newton-Cotes rules (e.g. trapezoidal rule, Simpson's rule); use of composite rules.

  • Gauss quadrature (optimal choice of nodes);

  • Adaptive quadrature.

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