Question Details

eA denotes the exponential of a square matrix A. Suppose λ is an eigenvalue and v is the corresponding eigen-vector of matrix A.

Consider the following two statements :

Statement 1 : eλ is an eigenvalue of eA .

Statement 2 : v is an eigen-vector of eA .

Which one of the following options is correct?

Options

A

Statement 1 is true and statement 2 is false

B

Statement 1 is false and statement 2 is true.

C

Both the statements are correct

D

Both the statements are false.

Show Answer

Correct Answer :

Option C

Both the statements are correct

Solution :

The correct option is: Both the statements are correct.

Let us analyze the definition of the matrix exponential and the properties of eigenvalues and eigenvectors to verify both statements.

For a square matrix A, the matrix exponential eA is defined by the infinite Taylor series expansion:

eA = I + A + 12!A2 + 13!A3 + = k=01k!Ak

where I is the identity matrix of the same size as A, and A0=I.

We are given that λ is an eigenvalue of A corresponding to the eigenvector v. By definition, this means:
Av=λv (with v0)

Let us determine the effect of higher powers of A on the eigenvector v.
For k=2:
A2v=A(Av)=A(λv)=λ(Av)=λ2v
By mathematical induction, for any non-negative integer k, we have:
Akv=λkv

Now, we apply the matrix exponential eA to the eigenvector v:

eAv = k=01k!Akv

Using the linearity of matrix multiplication:

eAv = k=01k!(Akv)

Substituting Akv=λkv into the summation:

eAv = k=01k!λkv

Since the vector v is independent of the summation index k, we can factor it out to the right:

eAv = k=0λkk!v

The term in the parentheses is the standard Taylor series expansion for the scalar exponential function eλ:

eAv = eλv

This equation is of the form Bv=μv where B=eA and μ=eλ.
Therefore:
1. eλ is indeed an eigenvalue of eA (which confirms Statement 1 is true).
2. v is the corresponding eigenvector of eA (which confirms Statement 2 is true).

Since both Statement 1 and Statement 2 are true, both statements are correct.

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