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Code Regeneration in Accelerated Models

Changing the structure of your model causes rapid accelerator mode to regenerate the standalone executable, and for the accelerator mode to regenerate the target code and update (overwrite) the existing MEX-file. Changing the value of a tunable parameter does not trigger a rebuild.

Determine Whether Change Requires Rebuild

The accelerator and rapid accelerator modes use a checksum to determine if the model has changed, indicating that the code should be regenerated. The checksum is an array of four integers computed using an MD5 checksum algorithm based on attributes of the model and the blocks it contains.

  1. Use the Simulink.BlockDiagram.getChecksum function to obtain the checksum for your model. For example:

    cs1 = Simulink.BlockDiagram.getChecksum('myModel');

  2. Obtain a second checksum after you have altered your model. The code regenerates if the new checksum does not match the previous checksum.

  3. Use the information in the checksum to determine why the simulation target rebuilt.

For a detailed explanation of this procedure, see Determine Why Simulink Accelerator Is Regenerating Code.

Parameter Tuning in Rapid Accelerator Mode

In model rebuilds, rapid accelerator mode handles model configuration parameters and runtime parameters differently from other parameters.

Tune Model Configuration Parameters

To tune model configuration parameter values, you can:

  • Specify the parameter value on the Simulink.SimulationInput object that configures the simulation by using the setModelParameter function.

  • Programmatically change the configuration parameter value in the model using the set_param function.

  • Change the value in the model using the Configuration Parameters dialog box. To open the Configuration Parameters dialog box, in the Simulink® Toolstrip, on the Modeling tab, click Model Settings.

You can change some block diagram parameters during simulation without causing a rebuild, including the parameters listed in these tables.

Solver Parameters
AbsTolMaxConsecutiveZCsRefine
ConsecutiveZCsStepRelTolMaxOrderRelTol
ExtrapolationOrderMaxStepStartTime
InitialStepMinStepStopTime
MaxConsecutiveMinStepOutputTimes 

Loading and Logging Parameters
ConsistencyCheckingMaxDataPointsSaveOutput
DecimationMinStepSizeMsgSaveState
FinalStateNameOutputOptionSaveTime
LimitDataPointsOutputSaveNameStateSaveName
LoadExternalInputSaveFinalStateTimeSaveName
MaxConsecutiveZCsMsgSaveFormat 

Tune Runtime Parameters

The technique you use to tune runtime parameters in rapid accelerator simulations can affect whether the software rebuilds the rapid accelerator executable. Because rebuilding the executable can take significant time, avoiding rebuilds due to tuning parameters improves the efficiency of your rapid accelerator simulation workflow.

First, confirm that the parameters you want to tune are tunable and your model is set up to support tuning the desired parameters. To identify runtime parameters in your model, use the Simulink.BlockDiagram.buildRapidAcceleratorTarget. Directly tuning block parameter values in rapid accelerator simulations is not supported. When you want to tune a block parameter value in rapid accelerator simulations, define the block parameter value as a variable. Then, tune the variable value instead.

To tune runtime parameter values in your model without rebuilding the rapid accelerator executable, follow these steps:

  1. Create a Simulink.SimulationInput object to configure the simulation.

    simin = Simulink.SimulationInput(mdl);

  2. Use the setModelParameter function to set the SimulationMode parameter value to "rapid-accelerator" and the RapidAcceleratorUpToDateCheck parameter value to "off".

    simin = setModelParameter(simin,SimulationMode="rapid-accelerator");
simin = setModelParameter(simin,RapidAcceleratorUpToDateCheck="off");

  3. Use the setVariable function to specify the values to use for runtime parameters in the simulation. For example, this code configures the runtime parameter named param1 with a value of 10.

    simin = setVariable(mdl,"param1",10);

  4. Run the simulation using the SimulationInput object. For example, this code runs the simulation by specifying the SimulationInput object as an input argument for the sim function.

    out = sim(simin);

When you disable the rapid accelerator up-to-date check, you cannot tune parameters for the rapid accelerator simulation using the set_param function. The set_param function modifies the parameter in the model, while the SimulationInput object modifies the parameter only in the simulation. The configuration on the SimulationInput object is applied during simulation and reverts when the simulation completes.

For the rapid accelerator simulation to reflect changes you make to the model, you need to regenerate the rapid accelerator simulation target. Leaving the rapid accelerator up-to-date check enabled to tune parameter values using the set_param function can result in extra rapid accelerator target rebuilds compared to tuning parameter values using a SimulationInput object.

For more information about parameter tunability limitations, see Tunability Considerations and Limitations for Other Modeling Goals.

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