If M is diagonalizable, find a matrix N^3 = M

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In summary, The conversation is about finding a matrix N that satisfies the equation N^3=M, given that M is a diagonalizable matrix. The suggested solution is N=PD^(1/3)P^(-1), but it needs to be shown formally. The discussion also mentions the need to show that D^(1/3) always exists and that (D^(1/3))^3=D.
  • #1
victoranderson
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I have a question about diagonalizable matrix

So now I have showed M is a diagonalizable and I am asked to find a matrix N^3=M

Obviously if M=PDP^(-1)
then N=PD^(1/3)P^(-1) but I am wondering how to show it formally.
 
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  • #2
Given that ##N=PD^{1/3}P^{-1}##, what is ##N^3=NNN##?
 
  • #3
D H said:
Given that ##N=PD^{1/3}P^{-1}##, what is ##N^3=NNN##?
Strictly speaking, also need to show that this generates all solutions of the original equation.
 
  • #4
haruspex said:
Strictly speaking, also need to show that this generates all solutions of the original equation.
I'm not sure what you mean by that. Per the title of the thread, victoranderson has to find a matrix N such that N^3=M, not all matrices N such that N^3=M.

What he does need to show is that his D^(1/3) always exists and that (D^(1/3))^3=D.
 
  • #5
D H said:
I'm not sure what you mean by that. Per the title of the thread, victoranderson has to find a matrix N such that N^3=M, not all matrices N such that N^3=M.

What he does need to show is that his D^(1/3) always exists and that (D^(1/3))^3=D.
True.
 

1. What does it mean for a matrix to be diagonalizable?

Diagonalizable means that the matrix can be rewritten in diagonal form, where all the non-diagonal entries are equal to zero. This makes it easier to perform calculations and solve certain problems.

2. How do you know if a matrix is diagonalizable?

A matrix is diagonalizable if it has a full set of linearly independent eigenvectors. This means that the matrix can be transformed into diagonal form by using these eigenvectors.

3. What is the process for finding the matrix N^3 if M is diagonalizable?

If M is diagonalizable, it means that it can be written as M = PDP^-1, where P is a matrix of eigenvectors and D is a diagonal matrix with eigenvalues on the diagonal. To find N^3, we simply cube both sides of the equation, giving us N^3 = PD^3P^-1.

4. Can a non-square matrix be diagonalizable?

No, a non-square matrix cannot be diagonalizable because diagonalization requires finding a full set of linearly independent eigenvectors, which can only be done for square matrices.

5. Why is it useful to find the matrix N^3 if M is diagonalizable?

Finding N^3 can help us perform calculations and solve problems involving M more easily. It can also help us understand the behavior and properties of M, as the diagonal form of a matrix can reveal important information about its eigenvalues and eigenvectors.

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