Why use intermediate terms in Simscape?

Hi I'm writing my own blocks in Simscape and have come across intermediate terms. I have included a code snippet as demo:

 equations
    let
        Re = V*D*rho/mu;

    in
        x == y*Re;
    end

    Re == V*D*rho/mu;
    x == y*Re;
end

What is the difference of have my equations in "let/in" instead of just having it in equations?

/Jan

Answer 1

[Sebastian Castro]

There is an efficiency/memory vs. traceability difference.

If you defined Re explicitly as an intermediate variable, you need to allocate memory to that variable and track its value at each time step. The advantages

1. You can log the variable and view it later with tools like sscexplore.
2. It will show up in the block's "Variables" tab so you can set its initial condition, and you can see the initial value in the Variable Explorer.

If you use a let section, it basically inlines all that code and treats it as if it were just one big equation, as below. It is more efficient, but then you can't log the value for debugging/posterity.

    x == y*V*D*rho/mu;

- Sebastian