Resetting Integrator by output of state flow in Simulink

Hello,

i have a simulink model containing an integrator and a state flow diagram. The integrators output is an input to the state flow diagram and is multiplied with a value depending on the state of the state flow diagram.

The state flow diagram also outputs the current state, e.g. 1,2,3, etc. I would like to e.g. reset the integrator when the stateflow diagram reaches state 2. However, this configuration triggers an error in the simulation:

"'untitled/Chart' or the model referenced by it contains a block that updates persistent or state variables while computing outputs and is not supported in an algebraic loop. It is in an algebraic loop with the following blocks."

simulI am not sure why, since a simple reset of the integrators shouldn't call for such a behavior? In any way, does anybody has a suggestion on how to fix this issue?

Attached are screenshots of the model and the state flow diagram, as well as the model itself.

Answer 1

[Jonas]

Simulink cannot know which action to do first, since they depend on eachother. If you take output of the Stateflow s, reset the integrator, then the input of the Stateflow Int is different, which changes the state, which means it should NOT reset the integrator, which means the input of the Stateflow Int is different, which changes the state, which means ........ This is an algebraic loop.

Solution: add a Transport Delay block somewhere on the signal line marked in red.

[Philipp Pasolli]

Thanks for the hint with the time delay/transport delay Jonas.

I understand your reasoning for the Algebraic loop as you described it, meaning if the state change would be affected by the Int signal from the Integrator.

However the state changes in the example model are purely based on the simulation time and unaffected by the Integrators input. That's why i am confused about the algebraic loop message. Do you have any input to that too maybe?

[Jonas]

The Stateflow block calculates its outputs based on its inputs. So it first tries to determine all the inputs. It sees that the integrator block depends on the comparison block. It then sees that the comparison block depends on the output 's' of your Stateflow. Then it gets stuck because it did not determine the outputs of the Stateflow yet, because it was still trying to determine the inputs.

Indeed, a 'human' would be able to see-through the algebraic loop. There may be a few workarounds, by for example disabling the Algebraic Loop error in the Configuration Parameter settings? Maybe the Chart has a few settings, related to initialization. Don't have experience on this specific example.

[Philipp Pasolli]

Fair point, thanks for the clarification and suggestions.