# correct

Correct state and state estimation error covariance using extended or unscented Kalman filter, or particle filter and measurements

## Syntax

## Description

The `correct`

command updates the state and state
estimation error covariance of an `extendedKalmanFilter`

, `unscentedKalmanFilter`

or `particleFilter`

object using measured system outputs.
To implement extended or unscented Kalman filter, or particle filter, use the
`correct`

and `predict`

commands together. If the current output measurement exists, you
can use `correct`

and `predict`

. If the
measurement is missing, you can only use `predict`

. For information
about the order in which to use the commands, see Using predict and correct Commands.

`[`

corrects the state estimate and state estimation error covariance of an extended or
unscented Kalman filter, or particle filter object `CorrectedState`

,`CorrectedStateCovariance`

]
= correct(`obj`

,`y`

)`obj`

using
the measured output `y`

.

You create `obj`

using the `extendedKalmanFilter`

, `unscentedKalmanFilter`

or `particleFilter`

commands. You specify the state
transition function and measurement function of your nonlinear system in
`obj`

. You also specify whether the process and measurement
noise terms are additive or nonadditive in these functions. The
`State`

property of the object stores the latest estimated
state value. Assume that at time step `k`

,
`obj.State`

is $$\widehat{x}[k|k-1]$$. This value is the state estimate for time `k`

,
estimated using measured outputs until time `k-1`

. When you use the
`correct`

command with measured system output
`y[k]`

, the software returns the corrected state estimate $$\widehat{x}[k|k]$$ in the `CorrectedState`

output. Where $$\widehat{x}[k|k]$$ is the state estimate at time `k`

, estimated
using measured outputs until time `k`

. The command returns the
state estimation error covariance of $$\widehat{x}[k|k]$$ in the `CorrectedStateCovariance`

output. The
software also updates the `State`

and
`StateCovariance`

properties of `obj`

with
these corrected values.

Use this syntax if the measurement function *h* that you
specified in `obj.MeasurementFcn`

has one of the following forms:

`y(k) = h(x(k))`

— for additive measurement noise.`y(k) = h(x(k),v(k))`

— for nonadditive measurement noise.

Where `y(k)`

, `x(k)`

, and
`v(k)`

are the measured output, states, and measurement noise
of the system at time step `k`

. The only inputs to
*h* are the states and measurement noise.

`[`

specifies additional input arguments, if the measurement function of the system
requires these inputs. You can specify multiple arguments.`CorrectedState`

,`CorrectedStateCovariance`

]
= correct(`obj`

,`y`

,`Um1,...,Umn`

)

Use this syntax if the measurement function *h* has one of the
following forms:

`y(k) = h(x(k),Um1,...,Umn)`

— for additive measurement noise.`y(k) = h(x(k),v(k),Um1,...,Umn)`

— for nonadditive measurement noise.

`correct`

command passes these inputs to the measurement
function to calculate the estimated outputs.

## Examples

## Input Arguments

## Output Arguments

## More About

## Version History

**Introduced in R2016b**

## See Also

`predict`

| `clone`

| `extendedKalmanFilter`

| `unscentedKalmanFilter`

| `particleFilter`

| `initialize`

| `residual`