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Why I get different result at Simulink? (Matlab, Simulink)

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Why I get different results? (Matlab, Simulink)
My problem is that I get different results with Matlab (Transfer Function) and Simulink at closed loop.
Amplitude is different and when I zoom at Simulink's Plot I get this odd irregularity.

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Stefan Raab
Stefan Raab il 23 Apr 2016
I suppose that depends on the solver. The documentation of the "step" function describes in the "More About/Algorithms" section, that the sample time is chose automatically, fixed step if I remember correctly. In Simulink however, you might have used a variable step solver (probably ode45), which is more accurate generally. You can also execute the "step" function with a specified sample time, try a really small sample time as 1e-6 or 1e-7 as this should increase the accuracy. The command then would be:
t = 0:1e-6:10;
For the documentation on the step function, execute the following command:
web(fullfile(docroot, 'control/ref/step.html'))
Does this yield more accurate results?
Kind regards, Stefan
  2 Commenti
Bob il 23 Apr 2016
Thanks for your answer,
This fixed my problem. Now my results is correct.
%%Simulink Model
t = 0:1e-6:10;
Stefan Raab
Stefan Raab il 23 Apr 2016
I'm glad it works now. But I would use the t for the step function, not the Simulink model. The variable step solvers in Simulink are more powerful and now you force to simulate with a fixed step solver. This cannot adjust it's step size in order to achieve better accuracy and it cannot react to zero-crossings.

Accedi per commentare.

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