The value returned from getNumInputsImpl method must be a constant value. But the Value is immutable

Hi,

i get the following error when generating code:

The value returned from getNumInputsImpl method must be a constant value.  
Properties used in calculating this value must be Nontunable. 
The error occurred for MATLAB System block 'SiL_LUT_1D/MATLAB System1'.

The method:

function num = getNumInputsImpl(obj)
    num = obj.Approx.numInputs + 1; %  input
end

The propertie numInputs of Approx(ValueClass):

properties (SetAccess = immutable)
        numInputs = 0;
end

And obj.Approx is a nontunable Property of the System block. So for my understanding, this value can't change in anyway and should be interpreted as a constant value. Any suggestion on a fix or workaround?

[Thomas Kucharczyk]

A possible workaround is the creation of a vector with size numInputs and using the length of the vector:

num = length(obj.Approx.workaroundVector) + 1;

Answer 1

[Thomas Kucharczyk]

        function num = getNumInputsImpl(obj)
            if obj.numInputs ~= obj.Approx.numInputs + 1
                obj.numInputs = obj.Approx.numInputs + 1;
            end
            num = obj.numInputs; %  input
        end

The above approach with the Nontunable Property "numInputs" will give following error during code generation:

### Starting build procedure for model: SiL_LUT_1D
### Generating code and artifacts to 'Model specific' folder structure
 Code Generation  1
Elapsed: 1 sec
### Generating code into build folder: D:\masterarbeit\git\ols-library\Experiment\build\SiL_LUT_1D_ert_rtw
CGIR assertion 'T::isa((const Type*)aType)' failed in 'b:\matlab\src\cg_ir\export\include\cg_ir\type\type.hpp:528'
[  0] 0x000000055fdc6e8d                                  bin\win64\eml.dll+01011341 EML::COV::registerCoverageListener+00401597
[  1] 0x000000056015c191                                  bin\win64\eml.dll+04768145 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00574545
[  2] 0x00000005601643cd                                  bin\win64\eml.dll+04801485 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00607885
[  3] 0x00000005601721cd                                  bin\win64\eml.dll+04858317 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00664717
[  4] 0x000000056006731f                                  bin\win64\eml.dll+03765023 EML::NameCapture::verify+00736239
[  5] 0x00000005600648ea                                  bin\win64\eml.dll+03754218 EML::NameCapture::verify+00725434
[  6] 0x0000000560065258                                  bin\win64\eml.dll+03756632 EML::NameCapture::verify+00727848
[  7] 0x00000005601b1db4                                  bin\win64\eml.dll+05119412 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00925812
[  8] 0x00000005601239a9                                  bin\win64\eml.dll+04536745 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00343145
[  9] 0x0000000560130bdd                                  bin\win64\eml.dll+04590557 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00396957
[ 10] 0x0000000560054986                                  bin\win64\eml.dll+03688838 EML::NameCapture::verify+00660054
[ 11] 0x000000056004e94f                                  bin\win64\eml.dll+03664207 EML::NameCapture::verify+00635423
[ 12] 0x000000056004ed91                                  bin\win64\eml.dll+03665297 EML::NameCapture::verify+00636513
[ 13] 0x000000056008e194                                  bin\win64\eml.dll+03924372 EML::NameCapture::verify+00895588
[ 14] 0x00000005601239a9                                  bin\win64\eml.dll+04536745 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00343145
[ 15] 0x0000000560130bdd                                  bin\win64\eml.dll+04590557 CG::GenericTagCategory<EML::DesignRangeTag,0>::unregisterCategory+00396957
### Build procedure for model: 'SiL_LUT_1D' aborted due to an error.
Unexpected or internal error encountered in "in CGIR: b:\matlab\src\cg_ir\export\include\cg_ir\type\type.hpp line 528: T::isa((const Type*)aType)
". Please report this to MathWorks if you can cause it to recur
Component:Simulink | Category:Block diagram error

Answer 2

[Honglei Chen]

You said numInputs is nontunable, did you try to use Nontunable in the property defintion? Like

properties (Nontunable)
    numInputs = 0
end

HTH

[Thomas Kucharczyk]

"Properties may not be set in this method (it should leave the System object unchanged)."

Today i get the above error, yesterday i got a build error.

[Thomas Kucharczyk]

So, where can i change a property, i.e. obj.numInputs, when another property changes? Event handler won't work here too:

Code generation does not support function handles pointing to non-static methods.

    methods
        % constructor
        function obj = OLSEvaluator(varargin)
            
            setProperties(obj,nargin,varargin{:});
            
            % EventObject,  Property name, Event, static function handle
            addlistener(obj,'Approx','PostSet', @obj.handlePropEvents);
        end
        
        function handlePropEvents(obj, src, evnt)
            % return if not Approx property
            if strcmp(src.Name, 'Approx') == false
                return;
            end
            
            % return if not PostSet event
            if strcmp(evnt.EventName, 'PostSet') == false
                return;
            end
            
            % return if not a Approximator class
            if isa(obj.Approx, 'Approximator') == false
                return;
            end

            % add additional input for lambda (x_0 .. x_n, lambda)
            obj.numInputs = obj.Approx.numInputs + 1;
            
        end
    end

[Honglei Chen]

If it's numInputs is nontunable, then you cannot change it once the simulation starts. You can probably update it once in setupImpl.

[Thomas Kucharczyk]

setupImpls doesn't get called when updating the diagramm or making a change in the System block dialog. So it's not possible to change obj.numInputs to adjust the number of inputs. Therefore it's not possible to connect signals to the System block.

[Honglei Chen]

I was trying to explain for a nontunable property, you are not supposed to change it in your method. It looks like you are using a property, Approx, to control whether a port should be rendered? If so, I'd suggest you to define Approx as a nontunable property and use that one to return the number of inputs. You probably don't need an extra numInputs property.

HTH

[Thomas Kucharczyk]

The property Approx (obj.Approx) is already defined as a Nontunable property. This property gets a value class assigned with the property numInputs, which is set to immutable. But this approch gives the error from the initial question. My guess is, that this shouldn't happen, since you can't change any property of obj.Approx as it is a Nontunable property.

% Approx definition in the matlab system block
properties (Nontunable)
    Approx = [];
end
    

% Approx will be set to a value class of following definition:
classdef Approximator
   
    % Public, immutable properties
    properties (SetAccess = immutable)
        numInputs = 0;
        dimension;
    end

[Honglei Chen]

I see. You should be able to change Approx as long as the simulation has not started. I don't know the logic behind it but you shouldn't need to use listeners to control number of inputs. You can reference Approximator's properties in getNumInputsImpl too.

HTH

[Thomas Kucharczyk]

I have already used the property of Approximator to set the number of inputs. But code generation will fail using this approach. Please keep in mind, that this is only a problem for code generation, interpreted execution works fine.

[Thomas Kucharczyk]

Since Approx is a Nontunable property my suggestion is, that the code generator fails to descent into the Approx properties and mind the Nontunable attribute of Approx. This is a bug imho.

[Honglei Chen]

Hi Thomas, sorry I cannot help more without seeing the entire code. If you are willing to provide the complete code, I'd be happy to pass it to the corresponding team to investigate. Alternatively, you can contact the tech support to report the bug too.

[Thomas Kucharczyk]

Comment out following lines in exampleClass.m and the model will fork fine:

obj.phi = cell(1, numInputs);
for i = 1:numInputs
    obj.phi{i} = zeros(1, 10);
end

Don't forget to create the value class:

exampleObject = exampleClass(4);

[Thomas Kucharczyk]

"Code generation does not support assigning an object of a value class into a nontunable property. For example, obj.prop=v; is invalid when prop is a nontunable property and v is an object based on a value class." from MATLAB Classes Definition for Code Generation

This approach shouldn't even start code generation. Maybe there is a check missing for value classes which are set to a property?

[Honglei Chen]

Good suggestion, I'll create an enhancement request for the team, thanks.