Do we use closed loop or open loop information in Bode plot, Nyquist plot and Root Locus?
The bode plot is just a plot showing the frequency representation of your system. Any transfer function has one, hence you can use it to see the response of both closed or open loop. Nyquist and the root locus are mainly used to see the properties of the closed loop system. The root locus shows the position of the poles of the c.l. system as the gain of your controller changes. While nyquist diagram contains the same information of the bode plot. But instead of splotting two real graphs of the amplitude and the phase of the complex function the nyquist plot shows the same function in the complex plane