Why do I get "cannot load an object of class 'compactcl​assificati​onECOC'" after compiling a standalone application of a machine learning model?

I have a trained machine learning model saved as a MAT file that is loaded in my App Designer application.

When I compile the app into a standalone application with MATLAB Compiler, I get the following error when running it:

ERROR: cannot load an object of class 'compactclassificationECOC'

Answer 1

[MathWorks Support Team]

During the compilation process, a dependency analysis is run to pick up files that the code relies on. In this case, the dependent functions are specified as a  value in the trained model struct loaded through a MAT file. This causes the analysis to miss the necessary files.

To work around this, we can add a "function pragma" to the function to make the dependency explicit:

 % App designer method
        function myAppCallback(app, event)
            %#function classreg.learning.classif.CompactClassificationECOC
            [  additional code  ]

The "function pragma" was added based on the "ClassificationSVM" values in the trained model struct:

trainedModel = 

struct with fields:
predictFcn: @(x)exportableModel.predictFcn(predictorExtractionFcn(x))
ClassificationSVM: [1×1 classreg.learning.classif.CompactClassificationECOC]
About: 'This struct is a trained model exported from Classification Learner R2017b.'
HowToPredict: 'To make predictions on a new predictor column matrix, X, use: ...

Multiple functions can be added to the pragma with spaces:

%#function classreg.learning.classif.CompactClassificationECOC classreg.learning.regr.RegressionModel

Additional information about the "function pragma" can be found in the following link (see example 3 in particular):

https://www.mathworks.com/help/compiler_sdk/ml_code/function.html

Some of the warnings will remain, but those are known and expected and will not affect the functionality of the application.