# Documentation

## Inner Transitions

An inner transition is a transition that does not exit the source state. Inner transitions are powerful when defined for superstates with exclusive (OR) decomposition. Use of inner transitions can greatly simplify a Stateflow® chart, as shown by the following examples:

### Before Using an Inner Transition

This chart is an example of how you can simplify logic using an inner transition.

Any event occurs and awakens the Stateflow chart. The default transition to the connective junction is valid. The destination of the transition is determined by `[c1 > 0]` and ```[c2 > 0]```. If `[c1 > 0]` is true, the transition to `A1` is true. If ```[c2 > 0]``` is true, the transition to `A2` is valid. If neither `[c1 > 0]` nor `[c2 > 0]` is true, the transition to `A3` is valid. The transitions among `A1`, `A2`, and `A3` are determined by `E`, `[c1 > 0]`, and `[c2 > 0]`.

### After Using an Inner Transition to a Connective Junction

This example simplifies the preceding example using an inner transition to a connective junction.

An event occurs and awakens the chart. The default transition to the connective junction is valid. The destination of the transitions is determined by `[c1 > 0]` and ```[c2 > 0]```.

You can simplify the chart by using an inner transition in place of the transitions among all the states in the original example. If state `A` is already active, the inner transition is used to reevaluate which of the substates of state `A` is to be active. When event `E` occurs, the inner transition is potentially valid. If `[c1 > 0]` is true, the transition to `A1` is valid. If ```[c2 > 0]``` is true, the transition to `A2` is valid. If neither `[c1 > 0]` nor `[c2 > 0]` is true, the transition to `A3` is valid. This chart design is simpler than the previous one.

### Note

When you use an inner transition to a connective junction, an active substate can exit and reenter when the transition condition for that substate is valid. For example, if substate `A1` is active and `[c1 > 0]` is true, the transition to `A1` is valid. In this case:

1. Exit actions for `A1` execute and complete.

2. `A1` becomes inactive.

3. `A1` becomes active.

4. Entry actions for `A1` execute and complete.

See Process the First Event with an Inner Transition to a Connective Junction for more information on the semantics of this notation.

### Using an Inner Transition to a History Junction

This example shows an inner transition to a history junction.

State `Power_on.High` is initially active. When event `Reset` occurs, the inner transition to the history junction is valid. Because the inner transition is valid, the currently active state, `Power_on.High`, is exited. When the inner transition to the history junction is processed, the last active state, `Power_on.High`, becomes active (is reentered). If `Power_on.Low` was active under the same circumstances, `Power_on.Low` would be exited and reentered as a result. The inner transition in this example is equivalent to drawing an outer self-loop transition on both `Power_on.Low` and `Power_on.High`.

See Use of History Junctions Example for another example using a history junction.

See Inner Transition to a History Junction for more information on the semantics of this notation.