## Estimate State-Space Models with Free-Parameterization

The default parameterization of the state-space matrices A, B, C, D, and K is free; that is, any elements in the matrices are adjustable by the estimation routines. Because the parameterization of A, B, and C is free, a basis for the state-space realization is automatically selected to give well-conditioned calculations.

To estimate the disturbance model K, you must use time-domain data.

Suppose that you have no knowledge about the internal structure of the discrete-time state-space model. To quickly get started, use the following syntax:

```m = ssest(data) ```

or

```m = ssregest(data) ```

where `data` is your estimation data. `ssest` estimates a continuous-time state-space model for an automatically selected order between 1 and 10. `ssregest` estimates a discrete-time model.

To find a model of a specific order `n`, use the following syntax:

```m = ssest(data,n) ```

or

```m = ssregest(dat,n) ```

The iterative algorithm `ssest` is initialized by the subspace method `n4sid`. You can use `n4sid` directly, as an alternative to `ssest`:

```m = n4sid(data) ```

which automatically estimates a discrete-time model of the best order in the 1:10 range.