# Convert from One Model Type to Another

This example shows how to convert a numeric LTI model from one type (`pid`) to another type (`tf`).

In general, you can convert a model from one type to another type using the model-creation command for the target type. For example, you can use the `tf` command to convert an `ss` model to transfer function form, or use the `ss` command to convert a `zpk` model to state-space form.

Create a PID controller.

`pid_sys = pid(1,1.5,3)`
```pid_sys = 1 Kp + Ki * --- + Kd * s s with Kp = 1, Ki = 1.5, Kd = 3 Continuous-time PID controller in parallel form. ```

Convert `pid_sys` to a transfer function model.

`C = tf(pid_sys)`
```C = 3 s^2 + s + 1.5 --------------- s Continuous-time transfer function. ```

`C` is a `tf` representation of `pid_sys`. `C` has the same dynamics as `pid_sys`, but stores the dynamic parameters as transfer-function numerator and denominator coefficients instead of proportional, integral, and derivative gains.

You can similarly convert transfer function models to `pid` models, provided the `tf` model object represents a parallel-form PID controller with ${T}_{f}\ge 0$.

In general, you can use the technique of this example to convert any type of model to another type of model. For more specific information about converting to a particular model type, see the reference page for that model type.