Dialog box in the mask for different equations

Hi, I want to create a block that can do simple calculation, e.g. u^2, sqrt(u), etc, by selecting the function from the drop down menu

e.g.,

• if selection equal to a, do u^2
• selection is equal to b, do u + 3
• selection equal to c , do sqrt(u)

switch select
    case 'a'
        gain = u^2;
    case 'b'
        gain = u + 3;
    case 'c'
        gain = sqrt(u);
end

I have added the code to the mask Initialization. When I run the model, I get the error:

Undefined function or variable 'gain'.

Inside the mask is a Fcn block with the parameter gain.

Example code is in the attachment.

Answer 1

[Fangjun Jiang]

A few steps.

1. Change the name of the "Interpreted MATLAB Function" block to be "MyFun", so it's easy to reference it in the code.
2. Change the Initialization code to be below. The name of the function cannot be passed like in your original code.
3. Uncheck the "Evaluate" checkbox for the parameter "select". The value of the parameter "select" will be returned as 'a', or 'b' or 'c'. Otherwise, it will try to "Evaluate" the variable 'a', or 'b', or 'c' and then return the evaluated value to the parameter "select".

switch select
    case 'a'
        set_param([gcb,'/MyFun'],'MATLABFcn','u^2');
    case 'b'
        set_param([gcb,'/MyFun'],'MATLABFcn','u+3');
    case 'c'
        set_param([gcb,'/MyFun'],'MATLABFcn','sqrt(u)');

end

[Igor]

Thank you for the answer

Do you maybe know how to create a library block from this? When I do it, the selection gets hard-coded, and I cannot apply different option without breaking the link.

[Fangjun Jiang]

check the option "allow library blocks to modify its contents"

https://www.mathworks.com/help/simulink/ug/self-modifiable-link-subsystem.html