Why my level 2 s function runs very slow when the simulink is about taking the first step of integration?

Hi Guys

I implemented a block on level 2 s-function (implemented in m file) that does the same job as the built-in state-space function. When I compared the result, they produced the same result. However when I compared the elapsed time I noticed that my s function run slower than simulink build in block (in particular if the size of systems is very large (4000 states)). I noticed that the long simulation time occurs before simulink taking the first step of integration. After the first step, it run at comparable speed to state-space build in block. I realized it may be caused by the inefficiency in implementation. But any other reason for this?

Answer 1

[Birdman]

In the generated code, Level 2 S-function is called upon a pointer called SimStruct, which is used to call the output function of the system. Therefore, this situation slows down the application. To get rid of this, you can inline the S-function by either using S-Function Builder in Simulink from User Defined Functions library, or you can write a tlc file for your S-function by hand which is harder and requires more effort. For detailed information and documentation, please see the following links.

https://www.mathworks.com/help/rtw/tlc/inlining-s-functions.html?searchHighlight=inlining%2520s%2520functions&s_tid=doc_srchtitle

[Husni Rois Ali]

Hi Çevikalp Sütunç

Thank you for your reply. However i don't implement my s function in C

[Birdman]

I know that you don't but the reason that your S-function stays slow is the SimStruct data. If you generate code with ert.tlc, you will see the pointer structure.

[Husni Rois Ali]

Thank you again. But sorry to be honest I am not familiar with this. Just another simple question: If I use matlab functions such as eig(A),svd(A). Is your solution going to work?

[Birdman]

If you want to use matlab functions, you can embed them in a MATLAB Function in Simulink. You don't have to use them in S-function. The working principle of s-function is little bit different. I suggest you to read some documentation.