What is the composition of T and T in terms of linear transformations?

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Discussion Overview

The discussion centers around the composition of a linear transformation T defined as the projection of a vector v onto a non-zero vector u in R^2. Participants explore the properties of T, specifically focusing on the composition T(T(v)), and seek clarification on the implications of applying the projection twice.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks for clarification on the notation used for the composition T(T(v)), expressing uncertainty about its representation.
  • Another participant suggests that the composition involves taking the projection of the projection, questioning what happens to the vector after the first projection.
  • A later reply indicates that projecting a vector onto u for the first time "flattens" it in the direction of u, raising the question of the effect of a second projection.
  • One participant proposes that the length of the vector remains the same after the first projection, implying that the original projection formula could describe the composition.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the implications of the composition T(T(v)). There is no consensus on the outcome or interpretation of this composition, and the discussion remains unresolved.

Contextual Notes

Participants have not fully defined the implications of applying the projection transformation twice, leading to uncertainty about the resulting vector and its properties.

Who May Find This Useful

Readers interested in linear transformations, vector projections, and the properties of compositions of linear maps may find this discussion relevant.

BenZino11
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Let u (not equal to 0) be a vector in R^2 and let
T: v --> proju(v)

1. Show that T is a linear transformation.
2. Describe the composition T  T.
3. If ~u = [1,−1], find the standard matrix for T.

I'm good with 1 and 3, but I'm not sure what 2 is asking. Excuse the poor notation, it's my first time using this site.
 
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What are the little boxes supposed to be?
 
Sorry, I don't see little boxes. Maybe a computer issue but its just:

ToT (I'm not sure if this is T dot T or if the larger circle represents something else)

Thanks!
 
I see three boxes: T  T. It's probably a thing with the browser, IE 8.0 seems to be
unable to display certain characters.

If T(v) is the project of v onto u, what happens if you take the projection of the projection of v? I.e., what is T(T(v))?
 
( (u.[( (u.v)/(u.u) )u])/u.u ) u

Is that all?
 
You're missing my point. Once you project the vector for the first time, you have already "flattened" it out in the direction of u. What will happen if you try to flatten it out again?
 
The length will remain the same, as the projection of the vector v on u is the vector itself.
So I suppose to describe the composition I would just write out the original projection formula?
 

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