# Condensing variables of a matrix

I'm working with matrices such as

```
M = matrix([
[a, b, 0],
[c, 0, d],
[0, e, 0]])
```

where a, b, c, d, and e are variables. Then I loop through some numbers for each of a, b, c, d, and e, looking at the eigenvalues of the resulting matrix. $$ char(M) = x^3 - ax^2 - (bc + de)x + ade $$ So, I'm doing more work than necessary, and ideally, I'd reduce M down to

```
M = matrix([
[a, b, 0],
[1, 0, d],
[0, 1, 0]])
```

Is there a simple way of using Sage to do so?