Imagine that you have a pair of vectors ${\bf F}$ and ${\bf
Z}$
$$
{\bf F}=\pmatrix{1\cr 1 \cr 0}\quad {\bf Z}=\pmatrix{0\cr 1 \cr
1}
$$
Can you construct an example of a matrix $M$, other than the
identity, which leaves ${\bf F}$ fixed, in that $M{\bf F}={\bf F}$?
How many such matrices can you find? Which is the simplest? Which
is the most complicated?
Can you construct an example of a matrix $N$, other than the zero
matrix, which crushes ${\bf Z}$ to the zero vector ${\bf 0}$, in
that $N{\bf Z}={\bf 0}$? How many such matrices can you find? Which
is the simplest? Which is the most complicated?
Can you find a matrix which leaves ${\bf F}$ fixed and also crushes
${\bf Z}$?
Can you find any (many?) vectors fixed or crushed by the following
matrices? Give examples or convincing arguments if no such vectors
exist.
$$
M = \begin{pmatrix} 1&0&0\\ 0&1&0\\ 0&0&1\\
\end{pmatrix}, \begin{pmatrix} 1&2&3\\ 2&3&4\\
3&4&5\\ \end{pmatrix}, \begin{pmatrix} 1&-2&1\\
1&1&0\\ -2&1&-2\\ \end{pmatrix}
$$
Very hard extension:
Imagine that you are given a vector ${\bf F}$ and a vector ${\bf
Z}$. Investigate whether you will be able to make a matrix $M$
which both fixes ${\bf F}$ and crushes ${\bf Z}$.
NOTES AND BACKGROUND
Matrices are used to represent transformations of vectors; vectors
and matrices are usually studied together as an inseparable pair.
Although matrices and the rules of matrix multiplication might seem
abstract upon first encounter, they are actually very natural and
encode in an entirely meaningful way notions of symmetry and
transformation. This problem allows you to explore the effects
matrix multiplication has on various vectors. The eigenvectors of a matrix are
those vectors whose direction is unchanged by the action of the
matrix. The kernel of a
matrix is the set of vectors which are squashed to zero. Both
concepts are of fundamental importance in higher-level algebra and
its applications to science.