Using if/action blocks within an algebraic loop?

In Simulink, I am trying to use an algebraic loop to solve for a parameter. However, calculating this parameter requires a if/action block. Original code uses a Newton Raphson method, so I wanted to use an algebraic loop in place. It seems like it is not "allowed". I have "Input data dependency violation due action subsystems" and I'm pretty sure it's the feedback loop to create the algebraic loop.

In short: Is it possible to use if/action blocks within an algebraic loop? If not, then what other methods can I use?

Answer 1

[Guy Rouleau]

As you figured out, the algebraic loop solver uses a gradient descent method to solve the loop. The If/Else construct causes a discontinuity in the loop which is problematic for a gradient descent method.

When you have an algebraic loop, the blocks in the loop should be continuous both in time and values.

I recommend looking at the demo "sl_subsys_semantics". This demo contains many small models illustrating good and bad practices in this area.

very likely, you will need to either introduce a delay in the loop or rearrange your equations to avoid algebraic loops.