# How to interpret this matrix as a 1-dimension vector space?

I am studying some topics and I faced to the following statement:

[...] all tangent vectors are of this form, form the 1-dimensional vector space of real multiples of the matrix $$\begin{bmatrix} 0 & -1 \\ 1 & 0 \end{bmatrix}$$

It may be a naive question, but: how can I interpret/visualize this matrix as a 1-dimension vector space (a line)?

Edit 1: I am working with $$SO(2) \in \mathbb{S}^1$$.

Edit 2: This matrix is supposed to represent the tangent line of the unit circle at $$x=1$$.

• Identify $r\begin{bmatrix} 0 & -1 \\ 1 & 0 \end{bmatrix}$ with $r$. Or $-r$ if you like. – Elliot G Jun 10 at 19:35
• Hi @ElliotG , could you elaborate a bit more on your comment? I did not understand your point. Thanks. – Paulo Araujo Jun 10 at 19:56
• It depends what your question really is. If the goal is to interpret multiples of the matrix $A=\begin{bmatrix} 0 & -1 \\ 1 & 0 \end{bmatrix}$ as a $1$-dimensional vector space, the answer is just that the vectors are of the form $rA=\begin{bmatrix} 0 & -r\\ r & 0 \end{bmatrix}$ for any $r\in\Bbb R$. You can check $rA+sA=(r+s)A$ and $r(sA)=(rs)A$, for example. That's all it really means to be a vector space. – Elliot G Jun 10 at 20:33

Analogy

Consider the three dimensional space $$\mathbb R^3$$ and the vector $$v=(1,0,-1)^T$$. This vector defines a line containing all the vectors of coordinates $$(t,0,-t)$$ for $$t \in \mathbb R$$.

The given matrix (let’s call it $$A$$) can be used to define a line in a four dimensional space. The line contains all the matrices $$tA$$ for $$t \in \mathbb R$$.
• The $2 \times 2$ real matrices are a four dimensional linear space. And in any dimensional linear space a non zero vector (here a matrix) spans a one dimensional linear subspace, i.e. a « line ». – mathcounterexamples.net Jun 10 at 19:58
• If you have the unit circle $S^1$ in $\Bbb R^2$, the line tangent at $(1,0)$ can be visualized as the line $x=1$. Otherwise your question doesn't really make sense because a $2\times 2$ matrix is not an element of $\Bbb R^2$. Formally, though, the tangent space is just an abstract $1$-dimensional vector space, and nothing more. – Elliot G Jun 10 at 20:30
• You are right. I must edit the question. I am working with $SO(2) \in \mathbb{S}^1$. If I calculate the tangent space at $t=0$, I end up with something similar to what you commented in the original post. I was trying to visualize how that matrix ends up being a straight vertical line. That was the main question, if there is a way, at least in 2D, to visualize how the matrix becomes the tangent line. – Paulo Araujo Jun 10 at 20:42