Warning: foreach() argument must be of type array|object, bool given in /var/www/html/web/app/themes/studypress-core-theme/template-parts/header/mobile-offcanvas.php on line 20

For any n×n matrix A, show that ddtdetetA|r=e=trA

Short Answer

Expert verified
The derivative of the determinant of a matrix exponential at t=1 equals the trace of the matrix (ddtdetetA|r=e=trA). This is derived using properties of determinants, traces, and exponentials, and the final validation is done after substituting t=1 in the derivative equation.

Step by step solution

01

Understand the given equation

We are given ddtdetetA|r=e=trA. Here, det stands for determinant, tr for trace and etA for the matrix exponential, which is the sum n=0tnAnn!. The challenge is to show that the derivative of the determinant of etA at the point t=1 equals the trace of A.
02

Differentiate the determinant

It's a known fact that the derivative of the determinant is the determinant times the trace. Therefore, it can be derived that ddtdet(etA)=det(etA)tr(AetA).
03

Evaluate at t=1

When evaluated at t=1, this equation simplifies to ddtdet(etA)|t=1=det(eA)tr(AeA). Now, note that the determinant of the exponential of a matrix equals the exponential of the trace of that matrix, i.e., det(eA)=etr(A). Using this, the equation simplifies further to etr(A)tr(AeA). Finally, using the property that the trace of a matrix is scalar invariant, tr(AeA)=tr(A). Hence, we have etr(A)tr(A)=tr(A), which is true if t=1. Thus the equation ddtdetetA|r=e=trA, is validated.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Determinant
The determinant is a scalar value that is a key property of square matrices. It provides important information about the matrix, particularly in understanding its invertibility. For a square matrix A, the determinant, denoted as det(A), tells us whether the matrix is invertible. If det(A)=0, then A is not invertible, meaning that there is no matrix B such that AB=BA=I, where I is the identity matrix.
  • The calculation of the determinant varies with the size of the matrix. For a 2x2 matrix (ab cd), the determinant is adbc.
  • For larger matrices, determinants can be found using cofactor expansion or applications of matrix decomposition.
  • The determinant also helps in describing geometrical properties. For instance, the magnitude of the determinant of a 2x2 matrix can give the scale factor of the transformation described by the matrix.
Understanding determinants is critical because they appear in various branches of mathematics, including linear algebra and calculus. They are instrumental in solving linear equations, finding eigenvalues, and more.
Matrix Exponential
Matrix exponential, denoted by etA, is an extension of the classic exponential function to matrices. It is particularly useful in solving systems of linear differential equations and can describe continuous-time dynamical systems. The matrix exponential of A is defined by the power series:etA=I+tA+t2A22!+t3A33!+=n=0tnAnn!,where I is the identity matrix.
  • This series represents an infinite sum, but it converges for all matrices A, making etA well-defined.
  • The matrix exponential plays a significant role in transforming simple linear systems into solvable forms.
  • It holds the property that eA+B=eAeB when A and B commute.
The matrix exponential is also closely related to the concept of eigenvalues and eigenvectors of a matrix, which can simplify the computation of matrix exponentials under certain conditions.
Trace of a Matrix
The trace of a matrix, denoted tr(A), is the sum of the elements on the main diagonal of a square matrix. It is a straightforward concept but carries significant theoretical importance in various mathematical disciplines.
  • For a matrix A with elements aii along its diagonal, the trace is tr(A)=i=1naii, where n is the number of rows (or columns).
  • The trace is invariant under similar transformations, meaning that matrices A and B that are similar have the same trace.
  • The trace of a matrix is also an additive function, which means that tr(A+B)=tr(A)+tr(B).
The trace can be used in conjunction with other matrix properties, such as the determinant and eigenvalues, to discover interesting results, as seen in the original exercise. For instance, the proved equation demonstrates a relationship between the derivative of the determinant of a matrix exponential and the trace of the matrix.
Derivative
The concept of derivatives in mathematics measures how a function changes as its input changes. When extended to functions of matrices, the derivative takes on somewhat more complex meanings, especially with operations like determinant and matrix exponential.
  • In our context, differentiating the determinant of a matrix exponential requires us to understand how the determinant function behaves under differentiation.
  • Importantly, when differentiating the determinant det(etA), we use the fact that it results in the determinant multiplied by the trace,  det(etA)tr(AetA).
  • This derivative evaluation provides the result integrated within the problem, ddtdet(etA)|t=1=tr(A).
Derivatives in matrix analysis are crucial for dynamic systems, optimization problems, and understanding perturbations within theory and applications. The derivative of the determinant is a prime example of using calculus techniques in linear algebra contexts.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

See all solutions

Recommended explanations on Combined Science Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free