Signal Label Propagation

Propagated Signal Labels

When you enable the display of signal label propagation for output signals of the blocks listed in Blocks That Support Signal Label Propagation:

If there is a user-specified signal name that Simulink^® can propagate, the propagated signal label includes the name in angle brackets (for example, <sig1>).
If there is no signal name to propagate, Simulink displays an empty set of angle brackets (<>) for the label.

For example, in the following model, the output signal from the Subsystem block is configured for signal label propagation. The propagated signal label (<const>) is based on the name of the upstream output signal of the Constant block (const).

For more information on how Simulink creates propagated signal labels, see How Simulink Propagates Signal Labels.

Blocks That Support Signal Label Propagation

You can use signal label propagation with output signals for several connection blocks, which route signals through the model without changing the data. Connection blocks perform no signal transformation.

Also, Model blocks support signal label propagation.

The connection blocks that support signal label propagation are:

Enable
From
Function Call Split
Goto
Inport (subsystem only; not root inports)
Signal Specification
Subsystem (through subsystem Inport and Outport blocks)
Trigger
Two-Way Connection (a Simscape™ block)

The Bus Creator and Bus Selector blocks do not support signal label propagation. However, if you want to view the hierarchy for any bus signal, use the Signal Hierarchy Viewer.

The Signal Properties dialog box for a signal indicates whether that signal supports signal label propagation. The Show propagated signals parameter is available only for blocks that support signal label propagation. For details, see Display Propagated Signal Labels.

Display Propagated Signal Labels

You can display propagated signal labels for individual signals, or display the propagated signal labels for all signals in a model. To display the labels for all signals, from the Display menu in the Simulink Editor, select Signals & Ports > Propagated Signal Labels.

To display a propagated signal label for an individual signal:

Right-click the signal for which you want to display a propagated signal label and select Properties.
In the Signal Properties dialog box, select Show propagated signals.
The Show propagated signals parameter is available only for output signals from blocks that support signal label propagation.

To enable this signal property programmatically, create a handle to the signal line, and specify signalPropagation as 'on'. For example, you can use this code to enable or disable the property for all of the signals in a model diagram.

% Create an array of handles to every signal line in the diagram
signalLines = find_system(gcs,'FindAll','on','type','line');

% Enable or disable the property for each signal line
for i = 1:length(signalLines)

      % set(signalLines(i),'signalPropagation','off');
      set(signalLines(i),'signalPropagation','on');
end

If a signal already has a label, then an alternative approach for displaying a propagated signal label is:

In the model diagram, click the signal label.
Remove the label text.
In the signal label text box, enter an angle bracket (<).
Click outside the signal label.
Simulink displays the propagated signal label.

How Simulink Propagates Signal Labels

Understanding how Simulink propagates signal labels helps you to:

Anticipate the scope of the signal label propagation, from source to final destination
Configure your model to display signal labels for the signals that you want

For output signals from supported blocks, you can choose to have Simulink display propagated signal labels. For a list of supported blocks, see Blocks That Support Signal Label Propagation.

In general, Simulink performs signal label propagation consistently:

For different modeling constructs (for example, non-bus and bus signals, virtual and nonvirtual buses, subsystem and model variants, model referencing, and libraries)
In models with or without hidden blocks, which Simulink inserts in certain cases to enable simulation
At model load, edit, update, and simulation times

For information about some special cases, see:

General Signal Label Propagation Processing

In general, when you enable signal label propagation for an output signal of a block (for example, BlockA), Simulink performs the following processing to find the source signal name to propagate:

Checks the block whose output signal connects to BlockA, and if necessary, continues checking upstream blocks, working backward from the closest block to the farthest block.
Stops when it encounters a block that either:
- Supports signal label propagation and has a signal name
- Does not support signal label propagation
Obtains the signal name, if any, of the output signal for the block at which Simulink stops.
Uses that signal name for the propagated signal label of any output signals of downstream blocks for which you enable signal label propagation.

For example, in the following model, suppose that you enable signal label propagation for the output signal for the Subsystem block (that is, the signal connected to the Out1 port).

Simulink checks inside the subsystem, checks upstream from the From and GoTo blocks (which support signal label propagation and do not have a name), and then checks farther upstream, to the Constant block, which does not support signal label propagation.

Simulink uses the signal name of the Constant block output signal, const. The propagated signal label for the Subsystem output signal is <const>.

If the output signal from the Constant block did not have a signal name, then the propagated signal label would be an empty set of angle brackets (<>).

Suppose that in the Subsystem block you enable signal label propagation for the output signal from the In1 block, and you use the Signal Properties dialog box to specify the signal name const-from for the output signal of the From block, as shown below.

The propagated signal label for the Subsystem output signal changes to <const-from>, because that is the first named signal that Simulink encounters in its signal label propagation processing.

In the following model, the signal label propagation for the output signal of the Subsystem block uses the signal name bus1, which is the name of the output bus signal of the Bus Creator block. The propagated signal label does not include the names of the bus element signals (a and b).

Processing for Referenced Models

To enable signal label propagation for referenced models, in addition to the steps described in Display Propagated Signal Labels, use the default setting for the Model Configuration Parameters > Model Referencing > Propagate all signal labels out of the model parameter. In other words, make sure the parameter is enabled.

If you make a change inside a referenced model that affects signal label propagation, the propagated signal labels outside of the referenced model do not reflect those changes until after you update the diagram or simulate the model.

For example, the model ex_signal_label_prop_model_ref has a referenced model that includes an output signal from the In1 block that has a signal name of input_1.

If you enable signal label propagation for the signal from the Out1 port of the Model block, that signal does not reflect the name input_1 until after you update the diagram or simulate the model.

Processing for Variants and Configurable Subsystems

Simulink updates the propagated signal label (if enabled) for the output signal of the Subsystem or Model block, when both of these conditions occur:

The output signals for variant models have different signal names.
You change the active variant model or variant subsystem.

For Subsystem blocks, the signal label updates at edit time. For Model blocks, the update occurs when you update diagram or simulate the model.