# tf

Constructs a transfer function model.

## Syntax

* sys = tf()
* sys = tf('s')
* sys = tf(numerator, denominator)
* sys = tf(numerator, denominator, Ts)

## Input argument

* numerator - polynomial coefficients: a row vector or as a cell array of row vectors.
* denominator - polynomial coefficients: a row vector or as a cell array of row vectors.
* Ts - Sampling time Ts, default: in seconds
* sysIn - LTI model.

## Output argument

* sys - Output tranfer function system model.

## Description

sys = tf(numerator, denominator) is used to create a continuous-time transfer function model.

It is defined by specifying numerator and denominator of the transfer function.

When you include the Ts parameter, it allows you to create a discrete-time transfer function.

Setting Ts to -1 indicates an unspecified sampling time, and, in this scenario, the input arguments are treated as if they pertain to a continuous-time system.

## Examples

```matlab
numerator = 10;
denominator = [20, 33, 44];
sys = tf(numerator, denominator)
```

```matlab
numerator = 10;
denominator = [20, 33, 44];
Ts = 1.5;
sys = tf(numerator, denominator, Ts)
```

## See also

[ss](ss).

## History

| Version | Description     |
| ------- | --------------- |
| 1.0.0   | initial version |

## Author

Allan CORNET
