Use Variant Parameters to Reuse Block Parameters with Different Values - MATLAB & Simulink (original) (raw)

Main Content

You may have a set of requirements where the structure of the model remains the same, but the values of the parameters for each requirement are different. In this scenario, you can create a single model with fixed structure and create parameters with a finite set of values where each value corresponds to different requirements. Parameters that have multiple values are called variant parameters. Use the Simulink.VariantVariable class to create a variant parameter object.

Each value of a variant parameter must be associated with a variant condition expression. You can have multiple variant parameters associated with a variant condition, provided no two values belong to the same parameter. When a condition expression evaluates totrue, all the values associated with that condition become active and are assigned to the corresponding parameters. If you change the value of the variant control variable, a different set of values is assigned to the parameters. This way, variant parameters allow you to logically bind a set of values across different parameters to a condition expression, and the values are assigned to the parameter based on the variant condition that evaluates to true.

Simulink® selects the active value of a variant parameter during update diagram time, during code compile time, or during the model startup time. For more information, see Activate Variant During Different Stages of Simulation and Code Generation Workflow.

Consider this model. The Gain parameter of the Gain block is a variant parameter with its value set to K. The variable_K_ has two values: 3.5 and 8.5. Simulink chooses active value of K based on the value of the variant control variable V. If V==1 evaluates totrue, the value of K is set to 3.5. If V==2 evaluates to true, the value of_K_ is set to 8.5.

When to Create Variant Parameters

Variant parameters provide a way to design one model for many systems that differ in block parameter values. You can group different sets of values based on the system to simulate. Each set of values is associated with a variant condition expression. During simulation, if a variant condition evaluates to true, then all the values associated with that condition become active. To change the set of active values, change the value of the variant control variable and run the simulation again.

Consider this model that represents an automobile system with several configurations. These configurations, although similar in several aspects, can differ in values such as fuel consumption, engine size, or number of cylinders in the engine. Instead of designing multiple blocks that together represent all possible values, you can use variant parameters to model the varying values.

In this model, the Fuel consumption, Engine size, and Number of cylinders have variant parameters fc, es, and nc. The values of the variant parameters are based on the value of the variant control variableV. For example, if V==1 evaluates totrue, then the value of fc is set to30, es is set to 1000, andnc is set to 4.

Advantages of Using Variant Parameters

Using variant parameters in Model-Based Design provides several advantages:

• Variant parameters provide you a way to design one model for many systems.
• Variant parameters facilitate reuse of blocks. This approach improves workflow speed by reducing complexity.
• Variant parameters help you switch among different block parameter values for multiple simulation, code generation, or testing workflows.
• You are not required to regenerate the code for different values of a variant parameter because the generated code includes all variant values of the parameter when the variant activation time is set to code compile orstartup.
• You can use Variant Manager to manage and activate variant parameters in your model.

Limitations

• Variant parameters can only be defined in a base workspace, model workspace, or a data dictionary.
• Only the values of the variant parameters change based on the variant condition that evaluates to true. Other properties, such as storage class, data types, and so forth, remain the same irrespective of the variant condition.
• Variant parameters that are part of a variant parameter bank do not support AUTOSAR code generation.
• The Value property of the variant control variable (Simulink.VariantControl), which determines the active value of a variant parameter, must be one of these types:
  • Integer
  • Enumerated value
  • Simulink.Parameter object with value of type integer, enumeration, or a mathematical expression specified using theslexpr function.
  • User-defined type that inherits from Simulink.Parameter
• Using the slexpr function or aSimulink.data.Expression object directly to specify a mathematical expression for the value of a choice of a variant parameter or the variant control used by the variant parameter is not supported. Instead, define the value of the variant parameter or the variant control by using a Simulink.Parameter object with its value set to the mathematical expression by using theslexpr function.
• Using a Parameter Writer block to modify the value of theSimulink.VariantControl object used in aSimulink.VariantVariable object is not supported in these scenarios:
  • The Simulink.VariantControl value is modified in multipleInitialize Function blocks.
  • The condition expression of a Simulink.VariantVariable object contains multiple Simulink.VariantControl objects.
  • The Simulink.VariantVariable object is part of a variant parameter bank (Simulink.VariantBank).
  • The Parameter Writer block is connected to a block that uses a Simulink.VariantVariable object. In this case, theParameter Writer block supports only changing block parameter values.
  • The Simulink.VariantControl object is configured as a model argument.
  • The model is simulated in accelerator or rapid accelerator mode when theSimulink.VariantControl object is defined in the model workspace.
  • The Parameter Writer block is used to modify the value of aSimulink.Parameter object that is used as the value of a Simulink.VariantVariable choice.
  • The Simulink.VariantVariable object is used in an expression that contains multiple variables, for example, K + A where K is aSimulink.VariantVariable object andA is a MATLAB® variable.

See Also

Simulink.VariantVariable | Simulink.VariantControl | Simulink.VariantBank

Topics

• Create a Simple Variant Parameter Model
• Change Active Values and Activation Time of Variant Parameters
• Manage Variant Parameters Using Variant Manager
• Options to Represent Variant Parameters in Generated Code (Embedded Coder)