Proof That A & A^T Have the Same Nullspace (Kernel)

In summary, a nullspace, or kernel, is a set of vectors that result in a zero vector when multiplied by a matrix. Proving that A and A^T have the same nullspace is important because it shows linear dependence between the columns of A and rows of A^T, simplifying calculations and solving systems of equations. The nullspace of A and A^T are directly related, with any vector in one also being in the other. To prove this, one can set up a system of equations and use algebraic manipulations. This proof has implications in linear algebra, physics, and engineering, where matrices and systems of equations are commonly used.
  • #1
stanley.st
31
0
Hello,

can you help me with the proof? If A is normal
[tex]A^TA=AA^T[/tex]
then A and A^T have the same nullspace (kernel). And
[tex]||Ax||=||A^Tx||[/tex]

Thank you.
 
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  • #2
[itex] A^TAx = 0 = AA^Tx [/itex] for the vectors in the nullspace right?
 
  • #3
don't understand your hint.
 
  • #4
multiply both by [itex]x^T[/itex] from the left, what is the resulting expression in terms of norms?
 
  • #5
yes, I understand, thank you
 

Related to Proof That A & A^T Have the Same Nullspace (Kernel)

What is the definition of a nullspace?

A nullspace, also known as a kernel, is the set of all vectors that when multiplied by a matrix result in a zero vector.

Why is it important to prove that A and A^T have the same nullspace?

Proving that A and A^T have the same nullspace is important because it shows that the columns of A and the rows of A^T are linearly dependent. This can help simplify calculations and make solving systems of equations easier.

What is the relationship between the nullspace of A and the nullspace of A^T?

The nullspace of A and the nullspace of A^T are directly related. This means that any vector in the nullspace of A will also be in the nullspace of A^T, and vice versa.

How can you prove that A and A^T have the same nullspace?

To prove that A and A^T have the same nullspace, you can show that any vector in the nullspace of A is also in the nullspace of A^T, and vice versa. This can be done by setting up a system of equations and using algebraic manipulations to show that the nullspace of A is equal to the nullspace of A^T.

What implications does this proof have in linear algebra and other fields of science?

This proof has implications in linear algebra, as it helps simplify calculations and solve systems of equations. It also has applications in other fields, such as physics and engineering, where matrices and systems of equations are commonly used to model and solve real-world problems.

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