# polydata

Access polynomial coefficients and uncertainties of identified model

## Syntax

## Description

`[`

returns the coefficients of the polynomials `A,B,C,D,F`

] = polydata(`sys`

)`A`

, `B`

,
`C`

, `D`

, and `F`

that describe the
identified model `sys`

. The polynomials describe the
`idpoly`

representation of `sys`

as follows.

For discrete-time

`sys`

:$$A\left({q}^{-1}\right)y\left(t\right)=\frac{B\left({q}^{-1}\right)}{F\left({q}^{-1}\right)}u\left(t-nk\right)+\frac{C\left({q}^{-1}\right)}{D\left({q}^{-1}\right)}e\left(t\right).$$

*u*(*t*) are the inputs to`sys`

.*y*(*t*) are the outputs.*e*(*t*) is a white noise disturbance.For continuous-time

`sys`

:$$A\left(s\right)Y\left(s\right)=\frac{B\left(s\right)}{F\left(s\right)}U\left(s\right){e}^{-\tau s}+\frac{C\left(s\right)}{D\left(s\right)}E\left(s\right).$$

*U*(*s*) are the Laplace transformed inputs to`sys`

.*Y*(*s*) are the Laplace transformed outputs.*E*(*s*) is the Laplace transform of a white noise disturbance.

If `sys`

is an identified model that is not an
`idpoly`

model, `polydata`

converts
`sys`

to `idpoly`

form to extract the polynomial
coefficients.

`[`

also returns the uncertainties
`A,B,C,D,F`

,`dA,dB,dC,dD,dF`

]
= polydata(`sys`

)`dA`

, `dB`

, `dC`

,
`dD`

, and `dF`

of each of the corresponding polynomial
coefficients of `sys`

.

`[___] = polydata(`

returns the polynomial coefficients for the `sys`

,`J1,...,JN`

)`J1,...,JN`

entry in the array
`sys`

of identified models.

`[___] = polydata(___,'cell')`

returns all
polynomials as cell arrays of double vectors, regardless of the input and output dimensions
of `sys`

.

## Examples

## Input Arguments

## Output Arguments

## Version History

**Introduced before R2006a**