# retrodict

Retrodict filter to previous time step

## Description

The `retrodict`

function performs retrodiction, predicting
the state estimate and covariance backward to the time at which an out-of-sequence measurement
(OOSM) was taken. To use this function, specify the `MaxNumOOSMSteps`

property of the filter as a positive integer. After using this function, use the `retroCorrect`

or
`retroCorrectJPDA`

function to update the current state estimates using the OOSM.

`[`

retrodicts the filter by time `retroState`

,`retroCov`

] = retrodict(`filter`

,`dt`

)`dt`

, and returns the retrodicted state and
state covariance. The function also changes values of the `State`

and
`StateCovariance`

properties of the filter object to
`retroState`

and `retroCov`

, respectively.
Additionally, if the `filter`

is a `trackingIMM`

, the
function also changes the `ModelProbabilities`

property of the
`filter`

.

`[___,`

also returns the status of the retrodiction `retrodictStatus`

] = retrodict(___)`retrodictStatus`

as
`true`

for success and `false`

for failure. The
retrodiction process can fail if the length of the state history stored in the filter
(specified by the `MaxNumOOSMSteps`

property of the filter) does not
cover the request time specified by the `dt`

input.

## Examples

## Input Arguments

## Output Arguments

## More About

## References

[1] Bar-Shalom, Y., Huimin Chen, and M. Mallick. “One-Step Solution for the Multistep out-of-Sequence-Measurement Problem in Tracking.” *IEEE Transactions on Aerospace and Electronic Systems* 40, no. 1 (January 2004): 27–37.

[2] Bar-shalom, Y. and Huimin Chen. “IMM Estimator with Out-of-Sequence Measurements.” *IEEE Transactions on Aerospace and Electronic Systems*, vol. 41, no. 1, Jan. 2005, pp. 90–98.

## Extended Capabilities

## Version History

**Introduced in R2021b**

## See Also

`retroCorrect`

| `trackingKF`

| `trackingEKF`

| `objectDetectionDelay`