hasChangedFrom

Detect change in data from specified value in Stateflow chart

Syntax

tf = hasChangedFrom(data,value)

Description

tf = hasChangedFrom(data,value) returns 1 (true) if the value of data is equal to value at the beginning of the previous time step and is a different value at the beginning of the current time step. Otherwise, the operator returns 0 (false).

Examples

Detect Change in Matrix

Transition out of state if the previous value of the matrix M was equal to matrixValue and any element of M has changed value since the last time step or input event.

[hasChangedFrom(M,matrixValue)]

Detect Change in Matrix Element

Transition out of state if the element in row 1 and column 3 of the matrix M has changed from the value 7 since the last time step or input event.

In charts that use MATLAB^® as the action language, use:

[hasChangedFrom(M(1,3),7)]

In charts that use C as the action language, use:

[hasChangedFrom(M[0][2],7)]

Detect Change in Structure

Transition out of state if the previous value of the structure struct was equal to structValue and any field of struct has changed value since the last time step or input event.

[hasChangedFrom(struct,structValue)]

Detect Change in Structure Field

Transition out of state if the field struct.field has changed from the value 5 since the last time step or input event.

[hasChangedFrom(struct.field,5)]

Input Arguments

data — Data

scalar | matrix | structure | ...

Stateflow^® data, specified as a:

• Scalar

• Matrix or an element of a matrix

• Structure or a field in a structure

• Valid combination of structure fields or matrix elements

If data is a matrix, the operator returns true when it detects a change in one of the elements of data. You can also index elements of a matrix by using numbers or expressions that evaluate to an integer. See Operations for Vectors and Matrices in Stateflow.

If data is a structure, the operator returns true when it detects a change in one of the fields of data. You can also index fields in a structure by using dot notation. See Index and Assign Values to Stateflow Structures.

The argument data cannot be a nontrivial expression or a custom code variable.

Standalone charts in MATLAB do not support change detection on an element of a matrix or a field in a structure.

value — Value of data at previous time step

scalar | matrix | structure

Value of the data at previous time step, specified as the same data type of data. value must be an expression that resolves to a value that is comparable with data:

• If data is a scalar, then value must resolve to a scalar.

• If data is a matrix, then value must resolve to a matrix with the same dimensions as data.

  Alternatively, in a chart that uses C as the action language, value can resolve to a scalar value. The chart uses scalar expansion to compare data to a matrix whose elements are all equal to the value specified by value. See Assign Values to All Elements of a Matrix.

• If data is a structure, then value must resolve to a structure whose field specification matches data exactly.

Limitations

• Unable to be used within a Stateflow truth table.

Tips

• If multiple input events occur in the same time step, the hasChangedFrom operator can detect changes in data value between input events.

• If the chart writes to the data object but does not change the data value, the hasChangedFrom operator returns false.

• The type of Stateflow chart determines the scope of the data supported by the change detection operators:

  • Standalone Stateflow charts in MATLAB: Local only

  • In Simulink^® models, charts that use MATLAB as the action language: Input only

  • In Simulink models, charts that use C as the action language: Input, Output, Local, or Data Store Memory

• In a standalone chart in MATLAB, a change detection operator can detect changes in data specified in a call to the step function because these changes occur before the start of the current time step. For example, if x is equal to zero, the expression hasChangedFrom(x,0) returns true when you execute the chart ch with the command:

  step(ch,x=1);

  In contrast, a change detection operator cannot detect changes in data caused by assignments in state or transition actions in the same time step. Instead, the operator detects the change in value at the start of the next time step.

• In a chart in a Simulink model, if you enable the chart option Initialize Outputs Every Time Chart Wakes Up, using an output as the argument of the hasChanged operator always returns false. For more information, see Initialize outputs every time chart wakes up.

• When row-major array layout is enabled in charts that use hasChangedFrom, code generation produces an error. Before generating code in charts that use hasChangedFrom, enable column-major array layout. See Select Array Layout for Matrices in Generated Code.

Version History

Introduced in R2007a