Margin command help page
In the Matlab help editor, the textual description of the margin command is incorrect. It should read:
"[Gm,Pm,Wg,Wp] = margin(sys) computes the gain margin Gm, the phase margin Pm, and the corresponding crossover frequencies Wg and Wp, given the SISO open-loop model sys. Wp is the frequency where the gain is 0dB, and Wg is the frequency where the phase is -180°. This function handles both continuous- and discrete-time cases. When faced with several crossover frequencies, margin returns the smallest gain and phase margins."
The example plot and the "help margin" command give the correct descriptions of Wp and Wg.
--Julia Braman 13:19, 27 November 2007 (PST)