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Data Type Optimization Not Successful


You can use the fxpopt function or the Optimized Fixed-Point Conversion workflow in the Fixed-Point Tool to optimize the data types of a model or subsystem. Sometimes, the optimization is not successful. The following sections describe how to troubleshoot these cases.

Possible Solutions

Unable to Model Problem — No Constraints Specified

To determine if the behavior of a new fixed-point implementation is acceptable, the optimization requires well-defined behavioral constraints. Use the addTolerance method of the fxpOptimizationOptions class to specify numerical constraints for the optimized design. Alternatively, use blocks from the Model Verification library. For more information, see Specify Behavioral Constraints.

Unable to Model Problem — Model is not Supported

The model containing the system you want to optimize must have the following characteristics:

  • All blocks in the model must support fixed-point data types.

  • The design ranges specified on blocks in the model must be consistent with the simulation ranges.

  • If the model contains a MATLAB Function block, it must use MATLAB® language features supported for fixed-point conversion. For more information, see MATLAB Language Features Supported for Automated Fixed-Point Conversion.

  • The data logging format of the model must be set to Dataset.

    To configure this setting, in the Configuration Parameters, in the Data Import/Export pane, set Format to Dataset.

  • The model must have finite simulation stop time.

Data Type Conversion Blocks Were Ignored by Optimization

When the Input and output to have equal parameter of a Data Type Conversion block is set to Stored Integer (SI), the Data Type Conversion block will be ignored by the optimization.

Unable to Find a Fixed-Point Implementation that Met the Tolerances

If the optimization cannot find a feasible solution, try these solutions:

  • Relax signal tolerances.

  • Allow larger word lengths to expand the search space.

  • Consider using time windows when specifying signal tolerances. For more information, see Tolerance Computation.

  • Instead of specifying low-level tolerances on individual signals, consider specifying high-level behavioral constraints using blocks from the Model Verification library. For more information, see Specify Behavioral Constraints.

Unable to Explore Results

When the optimization is not able to find a new valid result, the fxpopt function does not produce an OptimizationResult output. Invalid results are most often the result of using a model that is not supported for optimization. For more information, see Unable to Model Problem — Model is not Supported.

When the optimization is successful, you can explore several different implementations of your design that were found during the optimization process. Do not save the model until you are satisfied with the new design. Saving the model disables you from continuing to explore the other implementations.

Resolve Error: The RowNames property must be a string array or a cell array, with each name containing one or more characters

This error may occur if clear all is used during fixed-point conversion workflows in the Fixed-Point Tool. clear all is currently not supported by fixed-point conversion workflows. Do not use clear all in initialization functions (InitFcn), or at the MATLAB Command Window when using the Fixed-Point Tool.

Derived Range Analysis Does Not Work for Accumulator Data Type

Only block output signals participate in derived range analysis. If a block has additional data type controls, such as for the accumulator or intermediate results, ranges are not derived for these elements. As a result, when optimization considers both simulation ranges and derived ranges, only simulation range information is used to optimize accumulator data types. Therefore, the optimized accumulator data type and output data type for a given block may differ. For more information, see How Range Analysis Works.

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