# Documentation

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## Discrete-Time Numeric Models

### Create Discrete-Time Transfer Function Model

This example shows how to create a discrete-time transfer function model using `tf`.

Create the transfer function $G\left(z\right)=\frac{z}{{z}^{2}-2z-6}$ with a sample time of 0.1 s.

```num = [1 0]; den = [1 -2 -6]; Ts = 0.1; G = tf(num,den,Ts) ```

`num` and `den` are the numerator and denominator polynomial coefficients in descending powers of z. `G` is a `tf` model object.

The sample time is stored in the `Ts` property of `G`. Access the sample time `Ts`, using dot notation:

`G.Ts`

### Other Model Types in Discrete Time Representations

Create discrete-time `zpk`, `ss`, and `frd` models in a similar way to discrete-time transfer functions, by appending a sample time to the input arguments. For examples, see the reference pages for those commands.

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