Is it better to use switch block or if-else block in Simulink?

Hi,

I have the following set of code in Matlab. I want to know, which is the best way to implement this code in Simulink (using switch block or if-else block!?).

If a > 0 c = m + n; else c = m - n; end

Thanks

Answer 1

[Birdman]

Well, in this kind of situations, it is better to use MATLAB Function block in Simulink since in case of code generation, MATLAB Functions are compatible for C code generation and several functions used in command line also become usable in Simulink by the help of MATLAB Functions. See the links below:

https://www.mathworks.com/help/simulink/slref/matlabfunction.html https://www.mathworks.com/help/simulink/ug/functions-supported-for-code-generation-alphabetical-list.html

Also, you may write a function for your algorithm as follows:

function c=SWITCH(a,m,n)
c=0;%initializing
   if(a>0)
   c=m+n;
   else
   c=m-n;
   end
end

where you have three inputs and one output. Hope this helps.

[Pallanti Srinivasa Rao]

Thank you so much for the reply.

Actually the variables that I have used as m and n are, two large Simulink functions.. I need to execute them, based on the condition of a. So, if I am using a switch block or the m-function (as u mentioned) for switch, does Simulink calculate functions m and n, and then executes the switch block? Or the vice versa...?

[Birdman]

Oh, I thought m and n are variables. If they are functions, then the situation will be different. I thought there is a 3 input-1 output function and you try to implement it. Now, I do not know if this is an answer for your question, but I read this sentence from the help documentation of Simulink Function:

You can call a Simulink Function block from a Function Caller block, a MATLAB Function block, or a Stateflow® Chart.

After reading this, what comes to my mind is this:

You calculate your functions m and n in your already defined Simulink Function blocks. Then, take those 2 outputs respectively from those blocks and give them as inputs to your MATLAB Function blocks. Meanwhile, you call m and n functions from your MATLAB Function block. Your third input will still be your condition, which is denoted by a. Then you make the calculations. Hope you understand what I mean. I suggest you not to use switch block in case of code generation. But if you find using switch block more useful for simulation purposes only, you may also use it.

[Pallanti Srinivasa Rao]

So in that case, I am calculating m + n and m - n, and then using a condition to get the output. Which is equivalent of the function:

c1 = m + n; c2 = m - n: if a > 0 c = c1; else c = c2; end

In which case, I am calculating the values for m+n and m-n before knowing the value of a. But however if we use if-else condition, this won't be the case. So I wanted know, is this the difference between if-else block and switch block (or the equivalent Matlab function)?

[Birdman]

Yes exactly. By the help of MATLAB Function, you will define if case within it and depending on the value of a, you will either calculate m+n or m-n. Therefore, you will operate only one calculation at a time step. This is really useful in case of code generation.

[Pallanti Srinivasa Rao]

Thank you so much. And thanks for the valuable inputs on code generation too.

[Birdman]

You are welcome. If my answer solves the issue, then accept the answer so that other people having the same problem will know there is a working solution.