# unitgain

Specify absence of nonlinearities for specific input or output channels in Hammerstein-Wiener models

## Syntax

```unit=unitgain ```

## Description

`unit=unitgain` instantiates an object that specifies an identity mapping F(x)=x to exclude specific input and output channels from being affected by a nonlinearity in Hammerstein-Wiener models.

Use the `unitgain` object as an argument in the `nlhw` estimator to set the corresponding channel nonlinearity to unit gain.

For example, for a two-input and one-output model, to exclude the second input from being affected by a nonlinearity, use the following syntax:

`m = nlhw(data,orders,['saturation''unitgain'],'deadzone')`

In this case, the first input saturates and the output has an associated `deadzone` nonlinearity.

## unitgain Properties

`unitgain` does not have properties.

## Examples

For example, for a one-input and one-output model, to exclude the output from being affected by a nonlinearity, use the following syntax:

`m = nlhw(Data,Orders,'saturation','unitgain')`

In this case, the input has a saturation nonlinearity.

If nonlinearities are absent in input or output channels, you can replace `unitgain` with an empty matrix. For example, to specify a Wiener model with a sigmoid nonlinearity at the output and a unit gain at the input, use the following command:

`m = nlhw(Data,Orders,[],'sigmoid');`

## Tips

Use the `unitgain` object to exclude specific input and output channels from being affected by a nonlinearity in Hammerstein-Wiener models. `unitgain` is a linear function $y=F\left(x\right)$, where F(x)=x. 