Code Generation of Parameter Objects With Expression Values

As described in Set Variable Value by Using a Mathematical Expression, you can set the value of a Simulink.Parameter object to an expression involving other MATLAB^® variables or parameter objects. When you generate code from a model that uses such a parameter object, to achieve your goal, use the information in the table.

Goal Technique and More Information

Goal	Technique and More Information
Generate code without Embedded Coder^®.	For the parameter object that uses the expression, apply an available storage class (see C Code Generation Configuration for Model Interface Elements). For the parameter objects used in the expression, apply only the storage class `Auto`.
Generate code that defines a global variable and initializes it by using an expression involving system constants and other macros (requires Embedded Coder).	See Initialize Parameter Value From System Constant or Other Macro (Embedded Coder) (Embedded Coder).
Generate code that defines a macro whose value is an expression involving other macros (requires Embedded Coder).	For the parameter object that uses the expression, apply a storage class that yields a macro in the generated code, such as `Define` (see Macro Definitions (#define) (Embedded Coder)). For the parameter objects used in the expression, apply storage classes that yield imported macros. For example, use the storage class `ImportedDefine`. Your external code must define these macros.

Generate code without Embedded Coder^®.

For the parameter object that uses the expression, apply an available storage class (see C Code Generation Configuration for Model Interface Elements).

For the parameter objects used in the expression, apply only the storage class Auto.

Generate code that defines a global variable and initializes it by using an expression involving system constants and other macros (requires Embedded Coder).

See Initialize Parameter Value From System Constant or Other Macro (Embedded Coder) (Embedded Coder).

Generate code that defines a macro whose value is an expression involving other macros (requires Embedded Coder).

For the parameter object that uses the expression, apply a storage class that yields a macro in the generated code, such as Define (see Macro Definitions (#define) (Embedded Coder)).

For the parameter objects used in the expression, apply storage classes that yield imported macros. For example, use the storage class ImportedDefine. Your external code must define these macros.

Considerations and Limitations

To avoid errors that prevent code generation, if you apply a storage class other than Auto to the dependent parameter object (which uses the expression as its value), the parameter objects used in the expression must use either Auto or a storage class that yields a macro in the generated code.
You cannot set the value of a parameter object that represents a symbolic dimension (see Implement Dimension Variants for Array Sizes in Generated Code (Embedded Coder)) to an expression.
With Embedded Coder, you can generate code that preserves the expression, but only for the purpose of statically initializing the value of a global variable or macro that corresponds to the dependent parameter object. Follow the guidelines in Expression Preservation.

Expression Preservation

If you want Embedded Coder to preserve expressions in the generated code, adhere to these restrictions and guidelines.

The dependent parameter object must use a storage class other than Auto. For example, to generate a global variable and initialize it by using the expression, use ExportedGlobal or ExportToFile.
The parameter objects used in the expression must:
- Use a storage class that yields a macro in the generated code, such as Define.
- Have scalar, real values if the expression uses operators.
The expression can use only these operators (in MATLAB syntax):
- Mathematical: +, -, *
- Relational: ==, ~=, <, >, <=, >=
These data typing guidelines apply:
- If possible, for a parameter object used in an expression, leave the DataType property at the default value, auto.
  To use a value other than auto, you must set the DataType property of the object that uses the expression to the same value. Otherwise, the code generator does not preserve the expression.
- If you want to use a parameter object in multiple different expressions, and the dependent parameter objects have different data types, leave the DataType property of the independent object at the default value, auto. In the generated code, the value of the macro is expressed as a floating-point number (with effective data type double), and the code initializes the dependent parameters by typecasting the result of each expression.

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