S-Function Level 1 vs S-Function Level 2

I have a problem. I have modeled a dynamic system( 5 inputs and 10 outputs) using S-Function Level-1 and Level-2. Both models work very well. My question is: Why the model that uses S-Function Level-2 runs its simulation very slowly? With the level 1 model simulation is very fast.

[want2know]

Dear Miguel,

I have read your post and I understand that you have successfully developed your system in S-function level 1.

Do you mind to spend a couples of minutes to read the following: please

I have been using S-function to do the following:

[a1, b1] = choose_cells(c, d);

where a1 and b1 are outputs, c and d are inputs. All the variables are having a single value, except d is an array with 6 values.

Referring to the image attached, we all know that in S-function block, the input dimension must be SAME as output dimension, else we will get error, in this case, the input dimension is 7 while the output dimension is 2, so I have to include the "Terminator" blocks in the diagram for it to work perfectly, otherwise, I will get an error.

My problem is, when the system gets bigger, the array d could contain hundreds of variables, using this method, it means I would have to add hundreds of "Terminator" blocks in order to get this work, this definitely does not sound practical.

Could you please suggest me a wise way to implement this?

Thanks in advance.

http://imgur.com/ib6BTTp

http://imageshack.us/content_round.php?page=done&id=4tHclZ2klaGtl66S36zY2KfO5co

Answer 1

[Miguel Montilla-DJesus]

How can I calculate CPU time when running the model in simulink???

Answer 2

[Kaustubha Govind]

I don't have a definite answer, and it's difficult to say not having seen your code, but it could be because Level-2 S-functions have a lot more features than Level-1 S-functions, so there is probably a lot of heavy-lifting/back-end work done by them? Exactly how slow are we talking about? Can you provide a ratio?

[Miguel Montilla-DJesus]

The level 1 model has an elapsed time equal to 7.139867 seconds.

The level 2 model has an elapsed time equal to 237.99 seconds

Both models have the same numbers of state variables (6) and 5 inputs and 10 outputs.

Answer 3

[Ben]

Profile your code but ticking the 'profile' entry in the Simulink tools menu.

You will probably see that the Level-2 function has its state functions called several thousand times more often than the Level-1 one does (for example my Level-1 function has its output function called ~6000 times, the Level-2 output function is called ~450,000 times!). This is the source of the slow-down, but I don't know how to fix it, sorry. Trying to work that out myself now!

Answer 4

[Ben]

Solved it for my particular simulation: I had direct feedthrough incorrectly enabled for an input port. This created an agebraic loop.