## Tunable Low-Pass Filter

In this example, you will create a low-pass filter with one tunable parameter a:

`$F=\frac{a}{s+a}$`

Since the numerator and denominator coefficients of a `tunableTF` block are independent, you cannot use `tunableTF` to represent `F`. Instead, construct `F` using the tunable real parameter object `realp`.

Create a real tunable parameter with an initial value of `10`.

`a = realp('a',10)`
```a = Name: 'a' Value: 10 Minimum: -Inf Maximum: Inf Free: 1 Real scalar parameter. ```

Use `tf` to create the tunable low-pass filter `F`.

```numerator = a; denominator = [1,a]; F = tf(numerator,denominator)```
```F = Generalized continuous-time state-space model with 1 outputs, 1 inputs, 1 states, and the following blocks: a: Scalar parameter, 2 occurrences. Type "ss(F)" to see the current value, "get(F)" to see all properties, and "F.Blocks" to interact with the blocks. ```

`F` is a `genss` object which has the tunable parameter `a` in its `Blocks` property. You can connect `F` with other tunable or numeric models to create more complex control system models. For an example, see Control System with Tunable Components.