# Unflatten a vector

I have a vector say a $9 \times 1$ vector which looks like $$\begin{bmatrix} 2x +1 \newline x \newline 1 \newline x \newline x^2 + 2x \newline 2x \newline x \newline 2x^2 \newline 0 \newline \end{bmatrix}$$ with entries in $\mathbb{F}_3[x]$.

There are 9 rows in this matrix and i want to write a function which takes an $n^2 \times 1$ matrix and turns it into a $n \times n$ matrix. So, in this case, we want the function would turn the above vector into

$$ \begin{bmatrix} 2x+1 & x & 1 \newline x & x^2+2x & 2x \newline x & 2x^2 & 0 \newline \end{bmatrix} $$

In this Sage, I tried this:

```
sage: v = Matrix(GF(3)[x], [[2*x+1],[x],[1],[x],[x^2+2*x],[2*x],[x],[2*x^2],[0]])
```

Then, write the following:

```
sage: Matrix(v.base_ring(), 3, 3, v)
```

This gave an error:

```
inconsistent number of rows: should be 3 but got 1
```