I know that a system with positive gain and phase margin is a stable system. And the one with a negative gain and phase margin is unstable. What will a system with negative phase margin and positive gain margin be ? Stable, Unstable or Marginally stable

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    $\begingroup$ You want both be positive, as far as I know. There are some assumptions in there about the system being minimum phase. $\endgroup$
    – Pete W
    Sep 22 '21 at 0:08
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    $\begingroup$ 1 Try drawing a bode diagram where one of the margins is negative and the other positive. You will see that the resulting shape of the bode diagram is different from most commonly encountered systems (AFAIK). 2 Remember that the first two sentences in your question are applicable only for systems which were open-loop stable to begin with. If you extend the concept of the margins to open-loop unstable systems, you can see systems where the one of the margins is negative, but still the system is stable. 3 I suggest that you include in your question the definitions of the two margins. $\endgroup$
    – AJN
    Sep 22 '21 at 12:25
  • $\begingroup$ @AJN Concept of margins to open-loop unstable ? Sorry I don't understand. Can you please elaborate more on this ? $\endgroup$
    – User12121
    Sep 22 '21 at 16:28
  • $\begingroup$ From the related questions on the sidebar. $\endgroup$
    – AJN
    Sep 22 '21 at 17:07

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