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I'm trying to make an application using Simulink but I'm encountering some mistakes. The output of my subsytem is a derivative of a variable, dw, then I use an integrator to integrate this variable and get w, then I feed back this system with this same variable and I get this message below.
"Cannot solve algebraic loop involving 'novo_modelo/Fuel Cell Stack/Anode Flow Model/Anode' because it consists of blocks that cannot be assigned algebraic variables, i.e., blocks with discrete-valued outputs, blocks with non-double or complex outputs, Stateflow blocks, or nonvirtual subsystems"
Why of this? Am I doing something wrong?

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回答（2 个）

Fangjun Jiang
Fangjun Jiang 2011-12-20

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It sounds like that the algebraic loop should not occur since you have an integrator, unless what you described of your model is not accurate.
See Algebraic Loops

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Danilo NASCIMENTO
Danilo NASCIMENTO 2011-12-20
So what I'm suppose to do,I need to integrate the function. I'm using an integrator block outside the subsystem.
Fangjun Jiang
Fangjun Jiang 2011-12-20
Can you re-examine your question? I am not sure if it's complete accurate, e.g. "the output of my subsystem is a derivative ...", should it be "the input"? There are ways to eliminate the algebraic loops in the link provided. Maybe you can post a snapshot of your model in your question.
Danilo NASCIMENTO
Danilo NASCIMENTO 2011-12-20
I'm trying to take a snapshot of my model but it is not working here.
It is File Exchange>>Submit a File, isn't it?
Danilo NASCIMENTO
Danilo NASCIMENTO 2011-12-20
The output of my system is exactly the derivative, that's why I pass it through the integrator to get the primitive variable.
Kaustubha Govind
Kaustubha Govind 2011-12-20
Is your subsystem atomic? Also, is the integrator placed inside the subsystem or outside of it?
Danilo NASCIMENTO
Danilo NASCIMENTO 2011-12-20
Where do I see whether it is atomic or not? And the integrator is within the subsystem.
Danilo NASCIMENTO
Danilo NASCIMENTO 2011-12-20
The problem is only with the integrator? There are other subsystems that are having the same mistake and they don't have integrator.

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Guy Rouleau
Guy Rouleau 2011-12-21

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I recommend taking the time to go through the algebraic loop section of the doc:
http://www.mathworks.com/help/toolbox/simulink/ug/f7-8243.html#f7-19688
This section contains multiple examples explaining what is an algebraic loop, an atomic subsystem and why it can lead to "artificial" algebraic loop.

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