# unscentedKalmanFilter

Create unscented Kalman filter object for online state estimation

## Description

`unscentedKalmanFilter`

creates an object for online state
estimation of a discrete-time nonlinear system using the discrete-time unscented Kalman filter
algorithm.

When you perform online state estimation, you first create the nonlinear state transition
function *f* and measurement function *h*. You then
construct the `unscentedKalmanFilter`

object using these nonlinear
functions, and specify whether the noise terms are additive or nonadditive.

After you create the object, you use the `predict`

command to predict state estimates at the next time step, and `correct`

to
correct state estimates using the unscented Kalman filter algorithm and real-time data. For
information about the algorithm, see Algorithms.

## Creation

### Syntax

### Description

creates an unscented Kalman filter object for online state estimation of a discrete-time
nonlinear system.`obj`

= unscentedKalmanFilter(`stateTransitionFcn`

,`measurementFcn`

,`initialState`

)

`stateTransitionFcn`

is a function that calculates the state of the system at time*k*, given the state vector at time*k*-1. This function is stored in the`StateTransitionFcn`

property of the object.`measurementFcn`

is a function that calculates the output measurement of the system at time*k*, given the state at time*k*. This function is stored in the`MeasurementFcn`

property of the object.`initialState`

specifies the initial value of the state estimates. This value is stored in the`State`

property of the object.

After creating the object, use the `correct`

and `predict`

functions to update state estimates and state
estimation error covariance values using a discrete-time unscented Kalman filter
algorithm and real-time data.

`predict`

updates`obj.State`

and`obj.StateCovariance`

with the predicted value at time step*k*using the state value at time step*k*–1.`correct`

updates`obj.State`

and`obj.StateCovariance`

with the estimated values at time step*k*using measured data at time step*k*.

additionally sets properties using name-value
arguments. If you do not specify the state transition function, measurement function,
and initial state values during creation, specify them using dot notation. For example,
for a two-state system with initial state values `obj`

= unscentedKalmanFilter(___,`Name,Value`

)`[1;0]`

, to specify
these values after creation, use `obj.State = [1;0]`

.

## Properties

## Object Functions

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

`predict` | Predict state and state estimation error covariance at next time step using extended or unscented Kalman filter, or particle filter |

`residual` | Return measurement residual and residual covariance when using extended or unscented Kalman filter |

`clone` | Copy online state estimation object |

## Examples

## Algorithms

The discrete-time unscented Kalman filter algorithm performs online state estimation of a discrete-time nonlinear system.

Consider a plant with states *x*, input *u*, output
*y*, process noise *w*, and measurement noise
*v*. Assume that you can represent the plant as a nonlinear system.

The algorithm computes the state estimates $$\widehat{x}$$ of the nonlinear system using state transition and measurement functions specified by you. The software lets you specify the noise in these functions as additive or nonadditive:

**Additive Noise Terms**— The state transition and measurements equations have the following form:$$\begin{array}{l}x[k]=f(x[k-1],{u}_{s}[k-1])+w[k-1]\\ y[k]=h(x[k],{u}_{m}[k])+v[k]\end{array}$$

Here

*f*is a nonlinear state transition function that describes the evolution of states`x`

from one time step to the next. The nonlinear measurement function*h*relates`x`

to the measurements`y`

at time step`k`

.`w`

and`v`

are the zero-mean, uncorrelated process and measurement noises, respectively. These functions can also have additional input arguments that are denoted by`u`

and_{s}`u`

in the equations. For example, the additional arguments could be time step_{m}`k`

or the inputs`u`

to the nonlinear system. There can be multiple such arguments.Note that the noise terms in both equations are additive. That is,

`x(k)`

is linearly related to the process noise`w(k-1)`

, and`y(k)`

is linearly related to the measurement noise`v(k)`

.**Nonadditive Noise Terms**— The software also supports more complex state transition and measurement functions where the state*x*[*k*] and measurement*y*[*k*] are nonlinear functions of the process noise and measurement noise, respectively. When the noise terms are nonadditive, the state transition and measurements equation have the following form:$$\begin{array}{l}x[k]=f(x[k-1],w[k-1],{u}_{s}[k-1])\\ y[k]=h(x[k],v[k],{u}_{m}[k])\end{array}$$

When you perform online state estimation, you first create the nonlinear state transition
function *f* and measurement function *h*. You then
construct the `unscentedKalmanFilter`

object using these nonlinear
functions and specify whether the noise terms are additive or nonadditive.

After you create the object, you use the `predict`

command to predict state estimates at the next time step, and `correct`

to
correct state estimates using the unscented Kalman filter algorithm and real-time data. For
additional details about the algorithm, see Extended and Unscented Kalman Filter Algorithms for Online State Estimation.

## Extended Capabilities

## Version History

**Introduced in R2016b**

## See Also

### Functions

`predict`

|`correct`

|`residual`

|`clone`

|`extendedKalmanFilter`

### Blocks

### Topics

- Nonlinear State Estimation Using Unscented Kalman Filter and Particle Filter
- Generate Code for Online State Estimation in MATLAB
- What Is Online Estimation?
- Extended and Unscented Kalman Filter Algorithms for Online State Estimation
- Validate Online State Estimation at the Command Line
- Troubleshoot Online State Estimation