The plant is absolutely unstable, we should NOT use them, but in this case both are clearly negative and a proportional controller will make the closed loop system absolutely unstable for unit gain

No, we cannot draw the Bode diagram and therefore we cannot measure any GM. If we want a PM we have to draw the root locus

GM is infinite and PM cannot be defined, therefore absolutely unstable closed loop system

The plant is marginally unstable, we are not sure to use them, but in this case both are clearly positive, and the closed loop system is stable for unit gain

The plant is absolutely unstable, we should not use them, but in this case we are lucky, GM is positive but PM is negative and it is true that the closed loop system would be unstable for unit gain

The plant is stable, the minimum values are positive for PM but negative for GM, so the closed loop system will be stable for unit gain

We cannot draw the Bode diagrams and whenever PM and GM cannot be identified we assume them to be infinite, and therefore the complete control system with unit controller and feedback will be stable

Yes, GM is infinite, and PM is negative (-172 degrees), therefore the complete control system with unit controller and feedback will be stable

As expected both GM (-16.9 dB) and PM (-172 degrees) are negative, therefore absolutely unstable closed loop system

The plant is marginally unstable, we are not sure to use them, but in this case we PM is positive but GM is negative and it is true that the closed loop system would be unstable for unit gain

The plant is marginally unstable, we are not sure to use them, but in this case we are lucky, GM is positive but PM is negative and it is true that the closed loop system would be unstable for unit gain

The plant is absolutely unstable, we should NOT use them, but in this case we are lucky, PM is infinite but GM is positive and it is true that the closed loop system would be stable for unit gain

The plant is absolutely unstable, we should NOT use them, but this case both are negative (GM negative infinite) and the closed loop system is unstable

PM and GM can only be used in continuous plants but we have discretized ours

Yes, PM is infinite and GM is negative, therefore the complete control system with unit controller and feedback will be absolutely unstable

The plant is absolutely unstable, we should NOT use them, in this case PM is positive but GM is negative and the closed loop system would be unstable for unit gain