Linear transformation and matrix transformation

Click For Summary

Discussion Overview

The discussion revolves around the relationship between linear transformations and matrix transformations, particularly in the context of finite and infinite dimensional vector spaces. Participants explore whether all linear transformations can be represented as matrix transformations and the implications of different bases and vector spaces.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants note that while every matrix transformation is linear, the reverse may not hold true in all cases, particularly when considering different vector spaces.
  • One participant argues that linear transformations can be represented by matrices, but this requires selecting a specific basis, especially in the context of R^n to R^m.
  • Another participant provides examples of linear transformations that are not matrix transformations, such as those involving non-matrix vector spaces and mappings from subspaces of R^3 to R^2.
  • Concerns are raised about the clarity of David Lay's textbook, with some participants expressing frustration over its treatment of linear transformations and matrix representations.
  • A participant emphasizes that every vector space can be coordinate-mapped onto R^n, suggesting that every linear transformation has a unique matrix representation when considering coordinate vectors.
  • One participant questions whether the definition of linear transformation being discussed is limited to finite dimensional vector spaces, noting the existence of infinite dimensional vector spaces.
  • Another participant confirms that their earlier statements about linear transformations being representable as matrices were indeed considering the finite dimensional case.

Areas of Agreement / Disagreement

Participants express differing views on whether all linear transformations can be considered matrix transformations, with some asserting that this is true only under certain conditions, while others provide counterexamples. The discussion remains unresolved regarding the implications of different vector spaces and bases.

Contextual Notes

Limitations include the potential confusion arising from the definitions of linear transformations and matrix transformations, particularly in relation to finite versus infinite dimensional vector spaces. The discussion also highlights the dependence on the choice of basis for representing linear transformations as matrices.

Ali Asadullah
Messages
99
Reaction score
0
Do all linear transformations are matrix transformation? In a book by David C Lay, he wrote on page 77 that not all linear tranformations are matrix transformations and on page 82 he wrote that very linear transformation from Rn to Rm is actually a matrix transformation. I know that every matrix transformation is linear but not sure about the reverse.
 
Physics news on Phys.org
Every linear transformation can be represented by a matrix multiplication. But writing a linear transformation as a matrix requires selecting a specific basis. If you are talking about R^n to R^m (there are other vector spaces) and are using the "standard" basis, then, yes, you can identify any linear transformation with a specific matrix and vice-versa.
 
See this post for more about the connection between linear operators and matrices.
 
Ali Asadullah said:
Do all linear transformations are matrix transformation? In a book by David C Lay, he wrote on page 77 that not all linear tranformations are matrix transformations and on page 82 he wrote that very linear transformation from Rn to Rm is actually a matrix transformation. I know that every matrix transformation is linear but not sure about the reverse.

I was wondering the same when I read that bit in the textbook! To answer your question, examples of linear transformations that are not matrix transformations are those that involve non-matrix vector spaces (eg. the vector space of polynomials) and the mapping from a planar subspace of R-3 onto R-2. These examples are given later in the text too, but unfortunately David Lay does not take the trouble to point out that these linear transformations in themselves are not matrix transformations (relating them back to his earlier claim that you quote). Note however that every vector space can be coordinate-mapped onto R-n, giving each of their vectors a unique column vector representation (for example, the coordinate vector of 4+ 3t^2 relative to the standard basis for P-2 is (4,0,3)). Thus, every linear transformation from a vector space V has a unique matrix representation after all! (The matrix acts on the coordinate vectors of the vectors in V, not the vectors in V themselves.)

David Lay's textbook is horrible as a reference text because the material is all over the place (especially on linear transformations), but he has some valid pedagogical reasons for structuring the book the way he does. He shouldn't have made that claim though, as it's an unimportant technicality at that point in the text that causes unnecessary confusion yet becomes patently self-evident later on.

Hope this message helps any future readers of David Lay's text!

ps. Btw, do think about _why_ a linear transformation cannot be a matrix transformation when the domain/codomain is a proper subspace of R-n (i.e. does not span the whole of R-n).:smile:

pps. For completeness, let me state that each matrix can of course represent many different linear transformations.
 
Last edited:
  • Like
Likes   Reactions: RamenDay
There are infinite dimensional vector spaces. Is the definition of linear transformation being discussed in this thread restricted to a mapping from one finite dimensional vector space to another? (I assume the definition of "matrix" that is being discussed refers to a finite dimensional array.)
 
Certainly, when I said "any linear transformation can be represented as a matrix", I was thinking of the finite dimensional case. Thanks for clarifying that.
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 12 ·
Replies
12
Views
5K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 1 ·
Replies
1
Views
4K
Replies
27
Views
5K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 0 ·
Replies
0
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K