Inverse matrices with scalar multiplication.

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Discussion Overview

The discussion revolves around the properties of inverse matrices in relation to scalar multiplication, specifically examining the expression \((\lambda T)^n\) and its implications for inverses. The scope includes theoretical aspects of linear algebra and matrix operations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses surprise at forgetting how to factor out a scalar multiple when dealing with inverse matrices, seeking confirmation of the expression \((\lambda T)^n = \lambda^n (T^n)\) for \(\lambda \in F\) and \(T \in L(V)\).
  • Another participant reiterates the expression and emphasizes that matrix multiplication can be viewed as the composition of linear maps, providing a specific example for \(n=2\) and suggesting that induction can be used to generalize this for all \(n\).
  • A later reply suggests that the established relationship should also hold for strictly negative values of \(n\), although this is not confirmed by others.
  • One participant confirms that if \(T\) is invertible and \(\lambda \neq 0\), then the inverse relationship \((\lambda T)^{-1} = \lambda^{-1} T^{-1}\) holds, providing a specific example to illustrate this point.

Areas of Agreement / Disagreement

Participants generally agree on the validity of the expressions discussed, particularly for positive integers and the case of invertible matrices. However, there is uncertainty regarding the application of these properties for negative values of \(n\), as this has not been definitively established in the discussion.

Contextual Notes

Some assumptions regarding the invertibility of \(T\) and the non-zero nature of \(\lambda\) are present but not explicitly stated in all contributions. The discussion does not resolve the application of the properties for negative integers.

brydustin
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I was surprised that I have never had to do this in so long and forgot the basic way to factor out a scalar multiple when a matrix is raised to a certain power (for example -1 for inverse matrices).

Basically, I just want some confirmation:

(λT)^n= λ^n (T^n ) ∶ for λ ϵ F and Tϵ L(V).
For example:
(λT)^(-1)=(1/λ) T^(-1)
or…. (λI-T)^(-1)=(1/λ) (I-T/λ)^(-1)
 
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we have tex, sup and sub tags. Request to use them.
 
brydustin said:
Basically, I just want some confirmation:

(λT)^n= λ^n (T^n ) ∶ for λ ϵ F and Tϵ L(V).
Remember that matrix multiplication is just composition of linear maps.

For all x we have

[tex]((\lambda T)\circ (\lambda T))(x)=(\lambda T)(\lambda (Tx))=\lambda(\lambda T(Tx))=\lambda^2(T\circ T(x))=(\lambda^2 T^2) x[/tex]

using linearity. So it holds for n=2. By induction it holds for all n.
 
Landau said:
Remember that matrix multiplication is just composition of linear maps.

For all x we have

[tex]((\lambda T)\circ (\lambda T))(x)=(\lambda T)(\lambda (Tx))=\lambda(\lambda T(Tx))=\lambda^2(T\circ T(x))=(\lambda^2 T^2) x[/tex]

using linearity. So it holds for n=2. By induction it holds for all n.

great! I thank this wraps up this thread then... I assume then that it holds for strictly negative values of n as well...
 
Yes, if T is invertible and lambda =/0 then

[tex](\lambda^{-1}T^{-1}\circ \lambda T)(x)=(\lambda^{-1}T^{-1})(\lambda Tx)=T^{-1}Tx=x[/tex]

hence

[tex](\lambda T)^{-1}=\lambda^{-1}T^{-1}.[/tex]
 

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