# poly1d

Class representing single-variable polynomial nonlinear estimator for Hammerstein-Wiener models

## Syntax

```t=poly1d('Degree',n) t=poly1d('Coefficients',C) t=poly1d(n) ```

## Description

`poly1d` is an object that stores the single-variable polynomial nonlinear estimator for Hammerstein-Wiener models.

You can use the constructor to create the nonlinearity object, as follows:

`t=poly1d('Degree',n)` creates a polynomial nonlinearity estimator object of `n`th degree.

`t=poly1d('Coefficients',C)` creates a polynomial nonlinearity estimator object with coefficients `C`.

`t=poly1d(n)` a polynomial nonlinearity estimator object of `n`th degree.

Use `evaluate(p,x)` to compute the value of the function defined by the `poly1d` object `p` at `x`.

## poly1d Properties

After creating the object, you can use `get` or dot notation to access the object property values. For example:

```% List all property values get(p) % Get value of Coefficients property p.Coefficients```
Property NameDescription
`Degree`

Positive integer specifies the degree of the polynomial
Default=`1`.

For example:

`poly1d('Degree',3)`
`Coefficients`

1-by-`(n+1)` matrix containing the polynomial coefficients.

## Examples

Use `poly1s` to specify the single-variable polynomial nonlinearity estimator in Hammerstein-Wiener models. For example:

`m=nlhw(Data,Orders,poly1d('deg',3),[]);`

where `'deg'` is an abbreviation for the property `'Degree'`.

## Tips

Use `poly1d` to define a nonlinear function $y=F\left(x\right)$, where F is a single-variable polynomial function of x:

`$F\left(x\right)=c\left(1\right){x}^{n}+c\left(2\right){x}^{\left(n-1\right)}+\dots +c\left(n\right)x+c\left(n+1\right)$`