Error while reducing sample time

Hi, I have a simulink model containing some algebraic loops.Input to the system is sine wave. When Sample time of this sine wave is 0(by default), simulation runs but I don't get the desired result, So I tried reducing it to 0.001 and when I did that, I got following error-

Simulink cannot solve the algebraic loop containing 'model/Sum' at time 0.001 using the TrustRegion-based algorithm due to one of the following reasons: the model is ill-defined i.e., the system equations do not have a solution; or the nonlinear equation solver failed to converge due to numerical issues. To rule out solver convergence as the cause of this error, either a) switch to LineSearch-based algorithm using set_param('model','AlgebraicLoopSolver','LineSearch') b) reducing the ode45 solver RelTol parameter so that the solver takes smaller time steps. If the error persists in spite of the above changes, then the model is likely ill-defined and requires modification.

What does this mean? and how to get rid of this? Thanks

[Anuj]

Can somebody explain this please?? , as I get this error by changing some parameters also, I went through some previous Q/A on this topic, which suggest to include unit delay in system, but my system doesn't have a scope for unit delay.

Thanks again

[Walter Roberson]

Did you try (a) and (b) ?

[Anuj]

I tried (b), but it didn't work, And am not sure about how to go with (a).

[vijay sai]

If it's right, I think it has something to do with the step size...check it out..

[Walter Roberson]

At the MATLAB command prompt, give the command

set_param('model','AlgebraicLoopSolver','LineSearch')

except change 'model' to be the name of your model.

[Anuj]

This gives the same error... that means my model is faulty, right? But I don't understand why this error is generating only when I am changing certain parameters or step size? while for some values, its showing some results.

[Anuj]

@walter, can you please tell me, why is this happening and what should I do?

[Walter Roberson]

If you are still getting the same error after giving the above command, then the command did not have any effect: if it had then it would be using LineSearch instead of TrustRegion. Or so I would tend to think.

Why would it happen? If the model has no solutions after the change in parameters. If the only change in parameters was to lower the step size, then the implication would be that the equations have no solutions until a larger time.

You should consider posting your model.

I myself will probably will not be able to find anything wrong with your model as I have never used Simulink and do not have the product to test with. But someone else might have ideas.

[Anuj]

Thanks for your reply, I'll try to check my model again.