How to use inside a Simulink file a user-defined class previously written in matlab?

Dear reader,

I have created a simple class given below:

   classdef dummy3
         properties
             a = 0;
             b;
         end
         methods
             %constructor
             function obj = dummy3(a,b)
             % class constructor
                 if(nargin > 0)
                   obj.a = a;
                   obj.b = b;
                 end
             end
         end

         methods(Static = true)            
             function value = roll(numdays)
                 value = numdays;
             end
         end
     end

and let the object P be defined as:

P = dummy3(1,2)

The question is how can I use the variable P.a and how can I call the method P.roll(rand(1)) inside a Simulink file? For convenience, I'd prefer to use them inside a Matlab function, like this scheme:

where I've tried to place inside the code

y = P.a

which resulted in error "Undefined function or variable 'P'." Furthermore, replacing this line by

y = P.roll(rand(1))

yields the same error. I cannot understand why since I did add into File -> Model Properties -> Callbacks -> InitFcn the line of code

P=dummy3(1,2)

Thank you for your help.

Answer 1

[Sebastian Castro]

I found 2 main issues here:

First, methods of a class must have the object itself as the first argument. So, to correctly use the roll method, you may want to redefine it as:

function value = roll(obj,numdays)

Secondly, you need to create the object P in your MATLAB Function block. In other words, prior to calling P.roll(4), you should say:

P = dummy3(a,b);
val = P.roll(4);

- Sebastian

[Stefan]

Hi Sebastian,

Thanks for your post. Your solution regarding the second issue seems to work in Simulink. However this implementation has one big drawback: at each sampling time the object P needs to be created over and over, whereas it does not change at all from one sample time to another. I have the feeling this will slow down simulations execution time.

Instead, I would have preferred P to be created just once at the beginning of simulations (since object P does not modify at all throughout simulations) and only use its propery P.a and call the method P.roll(rand(1)) inside a Matlab function. By doing so, I am hoping to achieve faster simulations. Any idea how to achieve this?

Thank you.

[Sebastian Castro]

Yes -- sorry, I should have mentioned that. You can make P a persistent variable so it is created only on the first execution of the model.

persistent P;
if isempty(P)
P = dummy3(a,b);
end

- Sebastian

[Stefan]

Thank you very much for your time. I confirm this is indeed the functionality that I have been looking for. Additionally I have checked that it can be used for code generation purpose.