Preserve Variant Parameter Expressions from Mask Initialization in Generated Code

R2026b

This example uses:

This example shows how to control variant behavior and generate tunable code by defining variant controls and variant parameters in the mask initialization code of a masked subsystem. You can use this approach to create variant controls and variant variables in mask initialization code and preserve the variant expressions in generated code by using the supported mask initialization syntax.

In this workflow, you create a mask on the Variant Subsystem and define mask dialog parameters to accept the values that control variant behavior. In the mask initialization code, you use these mask dialog parameter values to create two Simulink.VariantControl objects: one that selects the active choice subsystem and one that selects the active values of a Simulink.VariantVariable object (variant parameter). You can then use this variant parameter as the parameter value inside the choice subsystems. Because the mask initialization code uses the supported syntax and sets the activation time to startup, the generated code preserves variant expressions for tunability and initializes variant parameter values in the model initialize function.

Explore Model

Open the model slexVariantParameterWithMaskInit.

model = "slexVariantParameterWithMaskInit";
open_system(model);

The model slexVariantParameterWithMaskInit uses a masked Variant Subsystem to select algorithm and sensor configuration through mask parameters. The model contains these components:

A Sine Wave source block with amplitude 5 and frequency 1 Hz provides the input signal.

A masked Variant Subsystem block named Algorithm contains two variant choices: ScalarProduct and TableLookup. ScalarProduct, with pGain as the corresponding variant parameter, multiplies the input by a gain and adds a constant value of 1. TableLookup, with pLUTData as the corresponding variant parameter, passes the input through a 1-D Lookup Table block with breakpoints [1 2 3 4 5] and lookup table data.

A mask on the Algorithm subsystem has two mask parameters, algoType and sensorMode. The enumeration class file AlgoTypes.m defines the values ScalarProduct and TableLookup. The enumeration class file SensorModes.m defines the values SensorModeA and SensorModeB. The model workspace contains the variables vAlgo and vSensorMode. The mask dialog parameter algoType is associated with vAlgo, and the mask dialog parameter sensorMode is associated with vSensorMode. When the value of vAlgo changes, the active choice subsystem changes between ScalarProduct and TableLookup. When the value of vSensorMode changes, the active variant parameter values change. As a result, the selected sensor mode determines the gain value used by the ScalarProduct choice or the table data used by the TableLookup choice.

An output port Out1 captures the processed output signal.

Define Variant Controls and Variant Parameters in Mask Initialization

The mask initialization callback file dSlexVariantParameterWithMaskInit.m uses the mask parameters to create Simulink.VariantControl objects and variant parameters in the mask workspace. The file uses algoType and sensorMode to create the variant control objects vAlgoInMask and vSensorModeInMask. The variant control vAlgoInMask selects the active choice subsystem. The variant control vSensorModeInMask selects the active values of the variant parameters pGain and pLUTData, which are created as variant parameters and used by child blocks inside the choice subsystems.

To preserve tunability in generated code, use the callback syntax shown in this example when you create variant controls and variant parameters from mask dialog parameters during mask initialization. For more information, see Preserve Tunability of Parameters That Are Modified or Created in Mask Initialization.

classdef dSlexVariantParameterWithMaskInit

%   Copyright 2026 The MathWorks, Inc.

    methods(Static)
        function MaskInitialization(maskInitContext)
            ws = maskInitContext.MaskWorkspace;
            % Create variant controls
            ws.set('vAlgoInMask', ...
                @()dSlexVariantParameterWithMaskInit.createComponentVariantControl(algoType));
            ws.set('vSensorModeInMask', ...
                @()dSlexVariantParameterWithMaskInit.createSensorVariantControl(sensorMode));
            % Create variant variables
            ws.set('pGain', ...
                @()dSlexVariantParameterWithMaskInit.createGainVariantVariable());
            ws.set('pLUTData', ...
                @()dSlexVariantParameterWithMaskInit.createLUTVariantVariable());
        end

        function outParam = createComponentVariantControl(algoType)
            outParam = Simulink.VariantControl('Value', algoType, ...
                'ActivationTime', 'startup');
        end

        function outParam = createSensorVariantControl(sensorMode)
            outParam = Simulink.VariantControl('Value', sensorMode, ...
                'ActivationTime', 'startup');
        end

        function outParam = createGainVariantVariable()
            outParam = Simulink.VariantVariable("Choices", ...
                {"vSensorModeInMask == SensorModes.SensorModeA", -0.25, ...
                 "vSensorModeInMask == SensorModes.SensorModeB", 0.25});
        end

        function outParam = createLUTVariantVariable()
            outParam = Simulink.VariantVariable("Choices", ...
                {"vSensorModeInMask == SensorModes.SensorModeA", [1 0.9 0.8 0.7 0.6], ...
                 "vSensorModeInMask == SensorModes.SensorModeB", [1 1.1 1.2 1.3 1.4]});
        end
    end
end

Generate Code

Generate code to verify that variant controls and variant parameters are preserved as tunable constructs in the generated code.

slbuild(model);

### Searching for referenced models in model 'slexVariantParameterWithMaskInit'.
### Total of 1 models to build.
### Starting top model code generation target build for: slexVariantParameterWithMaskInit
### Successful completion of build procedure for: slexVariantParameterWithMaskInit

Build Summary

Top model targets:

Model                             Build Reason                                                Status                        Build Duration
==========================================================================================================================================
slexVariantParameterWithMaskInit  Target (slexVariantParameterWithMaskInit.c) did not exist.  Code generated and compiled.  0h 0m 11.626s

1 of 1 models built (0 models already up to date)
Build duration: 0h 0m 13.331s

Review Generated Code

The generated code uses the exported global variables vAlgo and vSensorMode, which are associated with the mask dialog parameters, to control variant behavior at startup. To review the generated code:

In the C Code tab, select Open Report.
Open slexVariantParameterWithMaskInit.c. In the generated code, the model initialization function uses if-else logic to assign values to the variant parameters pGain and pLUTData based on the variant control variable vSensorMode.

cfile = fullfile("slexVariantParameterWithMaskInit_ert_rtw",...
   "slexVariantParameterWithMaskInit.c");
coder.example.extractLines(cfile, ...
    "/* Model initialize function */", ...
    "/* Model terminate function */", 1, 0);

/* Model initialize function */
void slexVariantParameterWithMaskInit_initialize(void)
{
  {
    int32_T i;
    static const real_T tmp[5] = { 1.0, 0.9, 0.8, 0.7, 0.6 };

    static const real_T tmp_0[5] = { 1.0, 1.1, 1.2, 1.3, 1.4 };

    /* Variant Parameters startup activation time */
    if (vSensorMode == SensorModeA) {
      /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
      slexVariantParameterWithMaskI_P.pGain = -0.25;

      /* End of Outputs for SubSystem: '<Root>/Algorithm' */
      for (i = 0; i < 5; i++) {
        /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
        slexVariantParameterWithMaskI_P.pLUTData[i] = tmp[i];

        /* End of Outputs for SubSystem: '<Root>/Algorithm' */
      }
    } else if (vSensorMode == SensorModeB) {
      /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
      slexVariantParameterWithMaskI_P.pGain = 0.25;

      /* End of Outputs for SubSystem: '<Root>/Algorithm' */
      for (i = 0; i < 5; i++) {
        /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
        slexVariantParameterWithMaskI_P.pLUTData[i] = tmp_0[i];

        /* End of Outputs for SubSystem: '<Root>/Algorithm' */
      }
    }
  }
}

The step function uses if-else logic to select between the two variant subsystem choices based on the variant control variable vAlgo. The function then computes the output by using the selected algorithm and parameter values.

coder.example.extractLines(cfile, ...
    "/* Model step function */", ...
    "/* Model initialize function */", 1, 0);

/* Model step function */
void slexVariantParameterWithMaskInit_step(void)
{
  real_T rtb_SineWave;

  /* Sin: '<Root>/Sine Wave' */
  rtb_SineWave = sin((real_T)slexVariantParameterWithMask_DW.counter * 2.0 *
                     3.141592653589793 / 49.0) * 5.0;

  /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
  if (vAlgo == ScalarProduct) {
    /* Outputs for Atomic SubSystem: '<S1>/ScalarProduct' */
    /* VariantMerge generated from: '<S1>/Out1' incorporates:
     *  Constant: '<S2>/Constant'
     *  Gain: '<S2>/Gain'
     *  Sum: '<S2>/Add'
     */
    slexVariantParameterWithMaskI_Y.Out1 = slexVariantParameterWithMaskI_P.pGain
      * rtb_SineWave + 1.0;

    /* End of Outputs for SubSystem: '<S1>/ScalarProduct' */
  } else if (vAlgo == TableLookup) {
    /* Outputs for Atomic SubSystem: '<S1>/TableLookup' */
    /* Outputs for Atomic SubSystem: '<Root>/Algorithm' */
    /* VariantMerge generated from: '<S1>/Out1' incorporates:
     *  Lookup_n-D: '<S3>/1-D Lookup Table'
     *  Sin: '<Root>/Sine Wave'
     */
    slexVariantParameterWithMaskI_Y.Out1 = look1_binlxpw(rtb_SineWave,
      slexVariantParameterWith_ConstP.uDLookupTable_bp01Data,
      slexVariantParameterWithMaskI_P.pLUTData, 4U);

    /* End of Outputs for SubSystem: '<Root>/Algorithm' */
    /* End of Outputs for SubSystem: '<S1>/TableLookup' */
  }

  /* End of Outputs for SubSystem: '<Root>/Algorithm' */

  /* Update for Sin: '<Root>/Sine Wave' */
  slexVariantParameterWithMask_DW.counter++;
  if (slexVariantParameterWithMask_DW.counter == 49) {
    slexVariantParameterWithMask_DW.counter = 0;
  }

  /* End of Update for Sin: '<Root>/Sine Wave' */
}

Limitations

This workflow has these limitations:

The workflow does not support code compile activation time.

The workflow does not support defining a variant bank in mask initialization.

You cannot use a Simulink.Parameter object defined in mask initialization to create a variant control object or variant parameter.

You cannot define a Simulink.VariantExpression object in mask initialization.

If you use a mask parameter to create a variant control object or variant parameter, the mask parameter must be tunable and set to evaluate.

The value of a variant control object cannot be an expression.

If a model argument passed from a top model to a referenced model is used as a mask parameter that defines a variant control in mask initialization, and the variant control determines a variant variable used as a child block parameter value, then simulation in rapid accelerator mode is not supported.