hasChangedFrom
Detect change in data from specified value
Description
returns tf
= hasChangedFrom(data
,value
)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
Input Arguments
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 returnsfalse
.The type of Stateflow chart determines the scope of the data supported by the change detection operators:
Standalone Stateflow charts in MATLAB:
Local
onlyIn Simulink® models, charts that use MATLAB as the action language:
Input
onlyIn Simulink models, charts that use C as the action language:
Input
,Output
,Local
, orData 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, ifx
is equal to zero, the expressionhasChangedFrom(x,0)
returnstrue
when you execute the chartch
with the command: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.step(ch,x=1);
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 returnsfalse
. 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 usehasChangedFrom
, enable column-major array layout. See Select Array Layout for Matrices in Generated Code.
Version History
Introduced in R2007a