Matlab Function in simulink

Hi everyone,

I would like to create a Matlab Function in a simulink model. The function would be used in order to create a mask in which I can choose one over 4 different cases. For each one of this cases I would like to have a dedicated simulation stop time.

My code is this one:

function y = fcn(value)
 
T_sim=0;
if (value==1)
   T_sim = inf;
elseif (value==2)
    T_sim = 10;
elseif (value==3)
    T_sim = 15;
else
    T_sim = 20;
end
 
y = value;

I'm trying with this code, but I think that T_sim variable is local, and then outside from that function it has no effect. How can I solve it?

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/simulink/ug/controlling-execution-of-a-simulation.html#bq0htpd

If you look at the first diagram there, imagine using the output from your function block instead of a Constant block. You would compare to the Clock, and when the limit was reached, the STOP block would act.

[LODOVICO MANILDO]

Thanks for answering that fast, however its not usefull in this case, since the output of the function is the value itself.

I'm wondering to understand how can I update, let's say "automatically", the dedicated stop time variable, which in this case is called "T_sim".

I even tried to declare it as:

global T_sim;

But it doesn't work.

As you can see from the attached picture, the value is used to select one of the four possible speed references which have different durations.

[Walter Roberson]

Well, don't do that then: make T_sim a second output from the MATLAB Function Block.

If you are for some reason required to make T_sim a global variable in order to access it from other places, then you have to register it as a datastore https://www.mathworks.com/help/simulink/ug/model-global-data-using-data-stores.html

... but it seems to me much easier to just emit it from the function block as an additional output.