# Documentation

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# d2d

Resample discrete-time model

## Syntax

```sys1 = d2d(sys, Ts)sys1 = d2d(sys, Ts, 'method')sys1 = d2d(sys, Ts, opts)```

## Description

`sys1 = d2d(sys, Ts)` resamples the discrete-time dynamic system model `sys` to produce an equivalent discrete-time model `sys1` with the new sample time `Ts` (in seconds), using zero-order hold on the inputs.

```sys1 = d2d(sys, Ts, 'method')``` uses the specified resampling method `'method'`:

• `'zoh'` — Zero-order hold on the inputs

• `'tustin' ` — Bilinear (Tustin) approximation

`sys1 = d2d(sys, Ts, opts)` resamples `sys` using the option set with `d2dOptions`.

## Examples

### Example 1

Consider the zero-pole-gain model

`$H\left(z\right)=\frac{z-0.7}{z-0.5}$`

with sample time 0.1 s. You can resample this model at 0.05 s by typing

```H = zpk(0.7,0.5,1,0.1) H2 = d2d(H,0.05) Zero/pole/gain: (z-0.8243) ---------- (z-0.7071) Sample time: 0.05 ```

The inverse resampling operation, performed by typing `d2d(H2,0.1)`, yields back the initial model H(z).

```Zero/pole/gain: (z-0.7) ------- (z-0.5) Sample time: 0.1 ```

### Example 2

Suppose you estimates a discrete-time model of a sample time commensurate with the estimation data (`Ts = 0.1 seconds`). However, your deployment application demands a faster sampling frequency (`Ts = 0.01 seconds`).

```load iddata1 sys = oe(z1, [2 2 1]); sysFast = d2d(sys, 0.01, 'zoh') bode(sys, sysFast)```

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### Tips

• Use the syntax `sys1 = d2d(sys, Ts, 'method')` to resample `sys` using the default options for`'method'`. To specify `tustin` resampling with a frequency prewarp (formerly the `'prewarp'` method), use the syntax ```sys1 = d2d(sys, Ts, opts)```. See the `d2dOptions` reference page.

• When `sys` is an identified (IDLTI) model, `sys1` does not include the estimated parameter covariance of `sys`. If you want to translate the covariance while converting the model, use `translatecov`.