# Finding e^A for 2x2 Matrix: Issues with Det(A-(Lambda)I)

• scienceman2k9
In summary, e^A for a 2x2 matrix is the exponential of the matrix A, calculated through the Taylor series expansion of e^x with the substitution of A. It is useful in various applications such as solving differential equations and representing complex systems in a simpler form. However, issues such as a zero determinant and non-converging Taylor series can arise when finding e^A. To overcome these issues, methods such as Jordan decomposition and alternative formulas can be used. In real life, e^A has applications in fields such as population growth, physics, economics, chemistry, and computer graphics.
scienceman2k9
I need to find e^A of this 2x2 matrix...A= 1 1
-1 -1

When I do det(A-(lambda)I) I get 0 for the eigenvalues, which makes no sense. Am I doing something wrong?

Probably not. If the matrix is singular then at least one of the eigenvalues will be zero
Hmm...
$$det(A-I \lambda )=(-\lambda+1)(-\lambda-1)+1=\lambda^2$$
So $0$ is a double root, and both of the eigenvalues are zero.

Why don't you see what happens if you apply this matrix to a vector?

Last edited:

## 1. What is e^A for a 2x2 matrix?

e^A for a 2x2 matrix is the exponential of the matrix A, where e is the base of the natural logarithm and A is a 2x2 matrix. It is calculated by taking the Taylor series expansion of e^x and substituting the matrix A for x. This results in a 2x2 matrix with real or complex values.

## 2. Why is there a need to find e^A for a 2x2 matrix?

Finding e^A for a 2x2 matrix is useful in many applications, such as solving differential equations, analyzing population growth, and understanding the behavior of systems in physics and engineering. It allows us to represent complex and nonlinear systems in a simpler form, making it easier to analyze and solve problems.

## 3. What are some issues that can arise when finding e^A for a 2x2 matrix?

One common issue is that the determinant of the matrix A-(lambda)I may be zero, which leads to a singularity in the calculation of e^A. This can happen when the matrix A has repeated eigenvalues or when it is not diagonalizable. Another issue is that the Taylor series expansion of e^x may not converge for certain matrices, resulting in an infinite series that cannot be computed.

## 4. How can we overcome the issues with Det(A-(Lambda)I) when finding e^A?

To overcome the issue of a zero determinant, we can use a method called the Jordan decomposition, which decomposes the matrix A into a diagonal matrix and a nilpotent matrix. This allows us to compute e^A even when the determinant is zero. To address the issue of a non-converging Taylor series, we can use alternative methods such as the Cayley-Hamilton theorem or the matrix exponential function formula.

## 5. Are there any applications of e^A for 2x2 matrices in real life?

Yes, there are many real-life applications of e^A for 2x2 matrices. For example, it is used in population growth models to predict the growth of populations over time. It is also used in physics to describe the behavior of systems with multiple state variables. Additionally, it has applications in economics, chemistry, and computer graphics.

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