During variant condition propagation, Simulink automatically assigns conditions to blocks. You can control how the variant condition propagates upstream and downstream in a model.
Consider this model.
In Simulink, click Simulation > Run to view the variant condition propagation to blocks.
Variant Source1 block has the
A==1 condition, which propagates backward and forward to the blocks connected to
Variant Source1 block. The variant condition propagates to
Gain4 block but does not propagate to the
Sine Wave1 block.
Scope block is unconditional and receives its inputs from the
Sine Wave1 block. Therefore, the
Sine Wave1 block is unconditional. If you remove the
Scope block, the variant condition propagates to the
Sine Wave1 block.
If you replace the
Scope block with any other block (including the
Terminator block), the
Sine Wave1 block remains unconditional.
A block is unconditional if at least one of its inputs is unconditional. The input side of the
Sum block is connected to
Gain5 (conditional) block and to the
Sine Wave2 (unconditional) block. Therefore, the
Sum block is unconditional.
You can use these concepts to create a Subsystem block that controls the propagation of variant conditions to both sides or to one side.
Consider the section of the model that is connected to the
Variant Source2 and
Variant Source3 blocks. When you simulate the model, the Variant condition from the
Variant Source2 block and the
Variant Source3 blocks propagates upstream and downstream.
Stop on both sides block between
Gain6 and the
Gain7 block prevents the Variant condition from propagating upstream or downstream. Double-click the
Stop on both sides block to view its components.
Stop on both sides block uses a
Terminator to stop the variant condition propagation on upstream of the
Subsystem block. To stop the condition propagation on the downstream side of the
Subsystem block, one of the inports is connected to
Ground (unconditional). Therefore, this arrangement stops the variant condition propagation upstream and downstream. Similarly, you can selectively stop the condition propagation of variant condition at upstream or downstream for a model. For example, if you remove the
Terminator block, variant condition propagates upstream but is stopped downstream.
Here, one input port of the Subsystem block is unconditional making the Subsystem block unconditional at input side and thus stopping the propagation of variant condition downstream.