There are numerous ways to call a function in Simulink block:
1. MATLAB function block - intend to generate code from your model.
2. Interpret MATLAB function block - if you don't care about code generation.
3. Fcn block - if you have trivial expression to evaluate.
4. Create a "function.m" file in the current directory and then according to the your requirement you can set the callbacks in the "File->Model properties->Callbacks".
Suppose, you want your function to get executed before the model runs, you can place the function name in the "InitFcn". There are other callbacks model as well to choose from.
