How many times does a Matlab Function in Simulink run in one time step

Hello,

I have a Matlab Function in a Simulink model. Because the Matlab Funtion is time-confusing, I just want it to run one time in a step. But it seems to run multiple (>5) times in a step. I was wondering whether the number of times a Matlab function runs in a step depends on the solver (ode1,ode4, etc) selected. Can anyone provide some insights into this question? Thank you.

Regards Pan

Answer 1

[Pan Zhao]

After struggling for one day, I found two main causes for my problem. The first one is that there was an algebraic loop in my model due to a missing setting in a S function, which made Simulink run the model MULTIPLE times in ONE time step to solve the algebraic loop. The second one is that the [Update Method] of my Matlab Function was set to be [inherited]. The problem disappeared after (1) removing the algebraic loop and (2) changing the [Update Method] to [discrete] and setting the [Sample Time] equal to the (fixed) step size of the model.

Hope this may help people who confront similar problems.

[Mounir guesbaya]

Dear Pan Zhao,

I have the same problem while using Level 2 S-function to run a matlab function (non-linear model) in simulink, where I have noticed that the matlab function was being excuted 5 times in every 1 sample time which gives a different result in simulink than the result found in matlab.

I already have understood how did you fix this problem but the thing is that i could not find how to change the [update method] to be [discret] as you recommanded, would you please give some instructions to achieve this step ?

Also, I'm using ODE45 as a solver in my matlab function, is it what you mean by "algebraic loop" ?

Thank you

[Mounir guesbaya]

Dear Pan Zhao,

I have found how i can change the [update method] to be [discret], but it still run the function multiple times in one sample time because of the ODE and i can get red of it because it is the solver of my non-linear model.. so, is there any other solution for this problem ??

Thank you

[Ben MacCallum]

I added a "Unit Delay" block on the line responsible for the algebraic loop and it solved my problem.

Answer 2

[Ankit Bhatnagar]

Hi,

There are ways to start the block after a particular major step time like using a Clock block from Simulink/Sources and using simulation time feature of a block but currently not possible to execute a block as an independent task in Simulink.

Please refer this MATLAB Answers post for further details:

• https://www.mathworks.com/matlabcentral/answers/262892-how-do-i-make-a-simulink-embedded-function-run-independent-of-the-time-step-of-the-model

[Pan Zhao]

Hi Ankit,

Thanks very much for your reply. I am sorry for my late response. Actually, I just want my Matlab Function to run once in a time step of the model, not asking it to run independent of the time step of the whole model. After struggling for a while, I found the problem with my model and the solution, which I will explain next in a separate answer to make them more noticeable to others.

Regards Pan