Why do I receive a class mismatch error when I pass an input to an Embedded MATLAB function in Simulink 6.5 (R2006b)?

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MathWorks Support Team 2009-6-27

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https://ww2.mathworks.cn/matlabcentral/answers/100648-why-do-i-receive-a-class-mismatch-error-when-i-pass-an-input-to-an-embedded-matlab-function-in-simul

I have an Embedded MATLAB function in a Simulink model that consists of the following code:

function [a, secondOutput]  = fcn(input)
    a.b = single(1);
    a.c = 1;
    secondOutput = 1;

I receive the following error when I run this model:

 Class mismatch (single ~= double).  The class to the left is the class of the left-hand side of the assignment. Function 'Embedded MATLAB Function' (#958.143.146), line 5, column 1:"a.b"

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Answer 1

MathWorks Support Team 2009-6-27

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https://ww2.mathworks.cn/matlabcentral/answers/100648-why-do-i-receive-a-class-mismatch-error-when-i-pass-an-input-to-an-embedded-matlab-function-in-simul#answer_109996

This issue occurs because the data type of the input is not explicitly specified and this causes Simulink to guess the data types of the variables in the Embedded MATLAB function. The expression 'single(1)' in the Embedded MATLAB function is guessed to be a scalar double rather than a single and this is the cause of the mismatch.

To work around this issue, you can:

1. Explicitly specify the data type of the input by opening the Model Explorer from the View menu, going to the 'MATLAB Embedded Function' subpane under 'example2', clicking on 'input' in the list of variables in the MATLAB Embedded Function and changing the Type of this variable to 'double'.

2. Let the statement 'secondOutput = 1' precede the statement 'a.b = single(1)'.

3. Remove the input from the Embedded MATLAB function - i.e. do not pass any inputs to the function.