MHB Ali's question at Yahoo Answers (ker f)

  • Thread starter Thread starter Fernando Revilla
  • Start date Start date
AI Thread Summary
Every subspace U of a finite-dimensional vector space V can be represented as the kernel of a linear transformation from V to V. By selecting a basis for U and extending it to a basis for V, a linear map can be defined that sends the basis vectors of U to zero while mapping the remaining basis vectors of V to themselves. The matrix representation of this transformation is block diagonal, indicating that the kernel consists precisely of the vectors in U. Thus, it is proven that U is indeed the kernel of the defined linear transformation. This demonstrates a fundamental property of vector spaces and their subspaces.
Fernando Revilla
Gold Member
MHB
Messages
631
Reaction score
0
Here is the question:

Prove that every subspace U of a finite dimensional vector space V is the kernel of a linear transformation from V to V.

Please help, it seems quite obvious but I have no idea how to start.

Thanks.

Here is a link to the question:

Subspaces, kernel of vector spaces? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.
 
Mathematics news on Phys.org
Hello Ali,

Suppose that $B_U=\{u_1,\ldots,u_r\}$ is a basis of $U$. According to the incomplete basis theorem, there exist vectors $u_{r+1},\ldots,u_n$ such that $B_V=\{u_1,\ldots,u_n\}$ is a basis of $V$. Define the linear map $$f:V\to V,\qquad\left \{ \begin{matrix}f(u_i)=0&\mbox{if}&1\le i \le r\\ f(u_i)=u_i&\mbox{if}&r+1\le i \le n\end{matrix}\right.$$ The matrix of $f$ with respect to $B_V$ is diagonal by blocks:$$A=\begin{bmatrix}{0_{r\times r}}&{0_{r\times (n-r)}}\\{0_{(n-r)r\times r}}&{I_{(n-r)\times (n-r)}}\end{bmatrix}$$ Then, $x\in V$ (with coordinates $X=(x_j)^T$ with respect to $B_V$) belongs to $\ker f$ if and only if $AX=0$ or equivalently, if and only if $$X=(\alpha_1,\ldots,\alpha_r,0,\ldots,0)^T\quad (\alpha_i\in \mathbb{K})$$ which are the coordinates of all vectors of $U$. That is, $\ker f= U$.
 
Suppose ,instead of the usual x,y coordinate system with an I basis vector along the x -axis and a corresponding j basis vector along the y-axis we instead have a different pair of basis vectors ,call them e and f along their respective axes. I have seen that this is an important subject in maths My question is what physical applications does such a model apply to? I am asking here because I have devoted quite a lot of time in the past to understanding convectors and the dual...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Back
Top