Is there already a function to normalize a transfer function?

I have:

```
TransferFunction{Continuous, ControlSystemsBase.SisoRational{Float64}}
-951.729934283765s^2
---------------------------------------------------------------------------------------
3.1777394243568e7s^3 + 7.907227012152197e6s^2 + 540639.1480777722s + 5918.8473721761775
```

and I would like all coefficients to be divided by -951.729934283765.

OK, wrote a function that does this myself:

```
function normalize(tf_::TransferFunction{Continuous, ControlSystemsBase.SisoRational{Float64}})
expr = tf_.matrix[1]
factor = expr.num.coeffs[end]
if factor == 0.0
return tf_
end
tf(reverse(expr.num.coeffs./factor), reverse(expr.den.coeffs./factor))
end
```

You are reaching deep into the internals of ControlSystems here. See the functions `numvec`

and `denvec`

which would make your implementation simpler and avoid using internals.

No, because there are many possible ways one could possibly normalize a transfer function, and different people prefer different conventions.