Plot and display

• black — Black-Nichols diagram of a linear dynamical system
• bode — Bode plot
• bode_asymp — Bode plot asymptote
• evans — Evans root locus
• gainplot — magnitude plot
• hallchart — Draws the Hall chart
• m_circle — plots the complex plane iso-gain contours of y/(1+y) (obsolete)
• nicholschart — Nichols chart
• nyquist — nyquist plot
• phaseplot — frequency phase plot
• sgrid — s-plane grid lines.
• show_margins — display gain and phase margin and associated crossover frequencies
• svplot — singular-value sigma-plot
• zgrid — zgrid plot